Re-evaluation of some of the B-complex vitamin requirements of broiler chickens and turkey poults fed corn-soybean meal diets

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Title:
Re-evaluation of some of the B-complex vitamin requirements of broiler chickens and turkey poults fed corn-soybean meal diets
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xvi, 191 leaves : ill. ; 28 cm.
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English
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Ruiz, Nelson, 1950-
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Subjects / Keywords:
Vitamin B complex   ( lcsh )
Poultry -- Feeding and feeds   ( lcsh )
Corn meal as feed   ( lcsh )
Soybean meal as feed   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1987.
Bibliography:
Includes bibliographical references (leaves 181-189).
Statement of Responsibility:
by Nelson Ruiz.
General Note:
Typescript.
General Note:
Vita.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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aleph - 000952741
notis - AER5096
oclc - 18893836
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AA00003796:00001

Full Text













RE-EVALUATION OF SOME OF THE B-COMPLEX VITAMIN
REQUIREMENTS OF BROILER CHICKENS AND TURKEY
POULTS FED CORN-SOYBEAN MEAL DIETS


















BY

NELSON RUIZ


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA


1987

































To my mentors

Dagoberto Caceres Rojas
Eduardo Calderon Gomez
Robert H. Harms
Alvaro Iregui Borda
Ottomario Marin Ramirez
















ACKNOWLEDGEMENTS


I wish to express my most sincere appreciation to

Dr. Robert H. Harms, chairman of the supervisory committee,

for his guidance and support during these years of academic

work at the University of Florida.

I am also indebted to Dr. Richard D. Miles,

Dr. Henry R. Wilson, and Dr. Carroll R. Douglas, members of

the supervisory committee, for their advice and assistance.

Special thanks are also extended to Dr. Jesse F.

Gregory from the Department of Food Science and Human

Nutrition and member of the supervisory committee for his

suggestions and advice in the writing of this dissertation.

I wish to express my thanks to Dr. Jack L. Fry,

Assistant Dean for Resident Instruction, for his advice and

support during my graduate work.

I wish to extend my deepest appreciation to

Dr. Ramon C. Littell and Mr. Steve B. Linda from the

Department of Statistics for their help and advice in

conducting the statistical analysis.

I am grateful to Dr. Harry S. Sitren, Dr. F. Ben

Mather, and Dr. Scott A. Woodward for their comments and

helpful suggestions.


iii









I also must express my thanks to Dr. David L. Wicker

and Dr. Mark E. Whitacre at Degussa Corporation for the

analyses of tryptophan.

I wish to express my gratitude to Mr. Stan Blomeley,

Mrs. Bunny Stafford, and Mrs. Darrae Norling from IFAS

Editorial for their assistance in the photographic work.

Many thanks are extended to Mr. David P. Eberst,

Mr. Alan R. Eldred, Mr. Gary B. Russell, and Mrs. Linda K.

Flunker for their valuable help at the Poultry Science

Department. Appreciation is expressed to Mr. W. Gary Smith

for his excellent work in the feed mill.

I wish to thank Mr. Raimundo Angulo, former General

Manager of Finca S.A. in Bogota, Colombia, for his help and

encouragement.

I am deeply indebted to Dr. Richard D. Miles, Mrs. Pam

Miles and to former Department Chairman Dr. James E. Marion

for their friendship, help, and encouragement.

My heartfelt appreciation is extended to my mother, Ana

Isabel Ruiz, my sisters, Luz Nelly and Maria Claudia, and my

brothers, Hernando and Mario, for their moral and financial

support and their endless encouragement.

Gratitude is also expressed to Mrs. Carmen Garzon de

Dussan, Mr. Julio Dussan, and Mrs. Rosita de Ferro for their

generosity at difficult times early in my life.

I give my most sincere thanks to my friends Jairo

Dussan, Tirso de P. Molina, and Ottomario Marfn for their

friendship and encouragement.

















TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS .................................... iii

LIST OF TABLES ...................................... viii

LIST OF FIGURES ............... ....................... xiii

ABSTRACT ............................................... xv

CHAPTERS

I INTRODUCTION ..................................... 1

II NIACIN STUDIES WITH BROILER CHICKENS ........... 10

The Niacin Requirement of Broiler Chickens
Fed a Corn-Soybean Meal Diet from One to
Twenty-One Days of Age ......................... 10

Introduction ........... .................. 10
Materials and Methods .................... 12
Results and Discussion .................... 15
Summary ......................................... 43

The Niacin Requirement of Broiler Chickens
Fed a Corn-Soybean Meal Diet from Three
to Seven Weeks of Age .......................... 44

Introduction ................................ 44
Materials and Methods ..................... 45
Results and Discussion .................... 48
Summary ...................................... 53

Quantification of the Tryptophan-Niacin
Conversion in Broiler Chicks Fed a Corn-
Soybean Meal Niacin-Deficient Diet ............. 54

Introduction .............................. 54
Materials and Methods .................... 55
Results and Discussion .................... 59
Summary .................. ... ..... ......... 85










Page


Comparison of the Biopotencies of Niacin
and Niacinamide for Broiler Chicks ............. 86

Introduction ..... ..... .... ...... ........ 86
Materials and Methods ..................... 88
Results and Discussion .................... 91
Summary ...................... ............. 99

III NIACIN STUDIES WITH TURKEY POULTS .............. 101

Niacin Requirement of Turkey Poults Fed
a Corn-Soybean Meal Diet ....................... 101

Introduction .............................. 101
Materials and Methods .................... 102
Results and Discussion ................... 105
Summary .................................... 124

Comparison of the Biopotencies of Niacin
and Niacinamide for Turkey Poults .............. 125

Introduction ...... ....... ....... ........... 125
Materials and Methods .................... 125
Results and Discussion .................... 127
Summary ...... ... ....... ............................ 131

IV RIBOFLAVIN STUDIES ............................. 133

The Riboflavin Requirement of Broiler
Chicks Fed a Corn-Soybean Meal Diet ............ 133

Introduction ......... ................. .. .133
Materials and Methods ..................... 134
Results and Discussion ................... 137
Summary ................ ... ................ 148

The Riboflavin Requirement of Turkey
Poults Fed a Corn-Soybean Meal Diet ............ 149

Introduction ............ ... ............... 149
Materials and Methods .................... 150
Results and Discussion ................... 153
Summary ...................... ............... 166

V PANTOTHENIC ACID STUDIES WITH TURKEY
POULTS ......................................... 168

Introduction ................ ................... 168
Materials and Methods .......................... 169
Results and Discussion ......................... 171
Summary .............. .............. ............ 176










Page

VI SUMMARY AND CONCLUSIONS ........................ 178

REFERENCES ........................................... 181

BIOGRAPHICAL SKETCH ........... ....................... 190


vii
















LIST OF TABLES


Table


2-1


2-2




2-3




2-4




2-5




2-6




2-7




2-8



2-9


Page


Composition of basal diets, niacin
studies with broiler chicks ............


Performance
days of age
niacin in a
(Experiment

Performance
days of age
niacin in a
(Experiment

Performance
days of age
niacin in a
(Experiment

Performance
days of age
niacin in a
(Experiment


of broiler chicks fed to 21
various levels of supplemental
corn-soybean meal diet
1) ..............................

of broiler chicks fed to 21
various levels of supplemental
corn-soybean meal diet
2) ..............................

of broiler chicks fed to 21
various levels of supplemental
corn-soybean meal diet
3) ............ ..................

of broiler chicks fed to 21
various levels of supplemental
corn-soybean meal diet
4) ..............................


The broken-line model equations for the
relationship between supplemental dietary
niacin and body weight of broiler chicks
at 21 days of age ...........................

Summary of results from four 21-day
battery experiments: body weight,
niacin requirement, feed, niacin, and
tryptophan intakes of broiler chicks ........

Composition of pre-experimental and
experimental diets, finisher niacin
study .......................................

Performance of broiler chicks at 7 weeks
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
between 3 and 7 weeks of age ................


viii









Table Page

2-10 Composition of the basal diets,
tryptophan to niacin conversion studies ..... 57

2-11 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
(Experiment 1) ................. ........... 60

2-12 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
L-tryptophan and supplemental L-tryptophan
plus pyridoxine in a corn-soybean meal
diet (Experiment 1) ............ .... ........ 61

2-13 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
L-tryptophan in a corn-soybean meal diet,
combined data for L-tryptophan and
L-tryptophan + pyridoxine (Experiment 1) .... 63

2-14 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
(Experiment 2) ............... ................ 66

2-15 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
L-tryptophan in a corn-soybean meal diet
(Experiment 2) .............. ................ 67

2-16 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
(Experiment 3) .......... .... ..... ........... 71

2-17 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
L-tryptophan in a corn-soybean meal diet
(Experiment 3) .............................. 72

2-18 Multiple regression equations for the
relationship between body weight of
broiler chicks at 21 days of age and
their niacin or tryptophan intakes .......... 73

2-19 Variation associated with tryptophan-
niacin conversion ratios determined with
broiler chicks grown to 21 days of age and
fed a corn-soybean meal niacin-deficient
diet .......................... .... .......... 76









Table Page

2-20 Comparative performance of three experi-
ments with broiler chicks at 21 days of
age fed various levels of supplemental
niacin or tryptophan in a corn-soybean
meal diet ................................... 84

2-21 Composition of the basal diets, niacin-
niacinamide biopotency studies with
broiler chicks .............................. 89

2-22 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
niacin and niacinamide in a corn-soybean
meal diet (Experiment 1) .................... 92

2-23 Performance of broiler chicks to 21 days
of age fed various levels of supplemental
niacin and niacinamide in a corn-soybean
meal diet (Experiment 2) .................... 93

2-24 Multiple regression equations for the
relationship between body weights of
broiler chicks at 21 days of age and
their niacin or niacinamide intakes ......... 94

2-25 The broken-line model equations for the
relationship between body weight of
broiler chicks at 21 days of age and
supplemental dietary niacin or
niacinamide ......... ........... ............. 95

3-1 Composition of the basal diet, niacin
studies with turkey poults ................. 103

3-2 Performance of turkey poults to 21 days
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
(Experiment 1) ...................... ........ 106

3-3 Performance of turkey poults to 21 days
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
(Experiment 2) ........ .. .................... 107

3-4 Performance of turkey poults to 21 days
of age fed various levels of supplemental
niacin in a corn-soybean meal diet
(Experiment 3) ............... ..... .......... 113











3-5 The broken-line model equations for the
relationship between supplemental dietary
niacin and body weight of turkey poults
at 21 days of age .......................... 116

3-6 Estimated niacin requirement of turkey
poults from one to 21 days of age for
maximum growth and prevention of leg
abnormalities, all values are expressed
as mg of niacin per kg of diet .............. 117

3-7 Niacin and tryptophan intakes (per gram
of body weight) of turkey poults from
one to 21 days of age, summary of three
experiments .................................. 120

3-8 Performance of turkey poults to 21 days
of age fed various levels of supplemental
niacinamide in a corn-soybean meal diet ..... 128

3-9 Multiple regression equations for the
relationship between body weights of
turkey poults at 21 days of age and
their niacin or niacinamide intakes ......... 129

3-10 The broken-line model equations for the
relationship between body weight of
turkey poults at 21 days of age and
supplemental dietary niacin or
niacinamide ............... .................. 130

4-1 Composition of basal diet, riboflavin
studies with broiler chicks ................ 135

4-2 Performance of broiler chicks fed
various levels of supplemental riboflavin
from one to 21 days of age in a corn-
soybean meal diet, combined data of two
experiments ...... ........... ................ 138

4-3 Composition of the basal diet, riboflavin
studies with turkey poults .................. 151

4-4 Performance of turkey poults to 21 days
of age fed various levels of supplemental
riboflavin in a corn-soybean meal diet
(Experiment 1) .............. ................ 154


Table


Page









Table Page

4-5 Performance of turkey poults to 21 days
of age fed various levels of supplemental
riboflavin in a corn-soybean meal diet
(Experiment 2) .............................. ...... 155

4-6 Performance of turkey poults to 21 days
of age fed various levels of supplemental
riboflavin in a corn-soybean meal diet,
combined data of Experiments 1 and 2 ........ 159

5-1 Composition of the basal diet,
pantothenic acid studies with turkey
poults .. ............................... ... 170

5-2 Performance of turkey poults to 21 days
of age fed various levels of supplemental
pantothenic acid in a corn-soybean meal
diet (Experiment 1) ......................... 172

5-3 Performance of turkey poults to 21 days
of age fed various levels of supplemental
pantothenic acid in a corn-soybean meal
diet (Experiment 2) ......................... 173

5-4 Performance of turkey poults to 21 days
of age fed various levels of supplemental
pantothenic acid in a corn-soybean meal
diet (Experiment 3) .............. ........... 175


xii
















LIST OF FIGURES


Figure Page

2-1 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 1 ................. .............. 22

2-2 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 2 ................................ 26

2-3 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 3 ......... ....................... 29

2-4 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 4 ............................... 32

2-5 Leg disorders in niacin-deficient broiler
chicks ..................... ............... .. 38

2-6 Regression of body weight of broiler chicks
at 21 days of age on niacin intake (XI) and
tryptophan intake (X2), Experiment 1 ........ 65

2-7 Regression of body weight of broiler chicks
at 21 days of age on niacin intake (Xl) and
tryptophan intake (X2), Experiment 2 ........ 70

2-8 Regression of body weight of broiler chicks
at 21 days of age on niacin intake (X1) and
tryptophan intake (X2), Experiment 3 ........ 75

3-1 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 1 ................................ 109


xiii










Figure


3-2 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 2 ................................ 111

3-3 The broken-line model applied to the
relationship between supplemental dietary
niacin and body weight at 21 days of age,
Experiment 3 .............. ......... ....... 115

3-4 Niacin deficiency in turkey poults .......... 123

4-1 The broken-line model applied to the
relationship between supplemental dietary
riboflavin and body weight at 21 days
of age .................... .................. 140

4-2 Riboflavin deficiency in broiler chicks at
21 days of age .............. ................ 144

4-3 Riboflavin deficiency in turkey poults at
21 days of age ....... .............. ......... 158

4-4 The broken-line model applied to the
relationship between supplemental dietary
riboflavin and body weight at 21 days
of age .. .................. ... .............. 161


xiv


Page
















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


RE-EVALUATION OF SOME OF THE B-COMPLEX VITAMIN
REQUIREMENTS OF BROILER CHICKENS AND TURKEY
POULTS FED CORN-SOYBEAN MEAL DIETS

By

Nelson Ruiz

May 1987

Chairman: Robert H. Harms
Major Department: Animal Science

Twelve experiments with broiler chickens and eight

experiments with turkey poults were conducted to re-evaluate

their requirement for niacin, riboflavin, and pantothenic

acid when fed corn-soybean meal diets. All experiments,

except one, were conducted in battery brooders during the

first 21 days of life.

The requirement of broiler chicks for niacin from 1 to

21 days of age was determined to be 34 mg per kg of diet.

Since the feed consumption of broiler chicks during the

first 3 weeks of life was not enough to meet their niacin

requirement with the niacin contained in the intact

ingredients, synthetic niacin supplementation was necessary

to maximize performance. However, for broiler chickens from

3 to 7 weeks of age, feed intake of a typical corn-soybean










meal diet was sufficient so that no supplemental niacin was

required to maximize performance.

The results of two of the three experiments conducted

with the objective of quantifying the tryptophan-niacin

conversion ratio in a practical diet allowed the preliminary

conclusion that a conversion ratio of approximately 54:1 is

likely to occur in broiler chicks from 1 to 21 days of age.

The niacin requirement of turkey poults from 1 to 21

days of age was estimated to be 44 mg per kg of diet. This

value is considerably lower than the recommendation by the

National Research Council of 70 mg of niacin per kg of diet.

The relative biopotencies of niacin and niacinamide

were evaluated using growth of broiler chicks to 21 days of

age as the criterion of comparison. No significant differ-

ences were obtained between niacin and niacinamide.

Riboflavin studies with both broiler chicks and turkey

poults indicated that the requirement for this vitamin

expressed as concentration of the diet was similar to that

determined 40 years ago. However, the deficiency is more

severe in modern strains of chicks and poults than in those

strains used in experiments approximately 40 years ago.

The results of three pantothenic acid studies with turkey

poults indicated that a corn-soybean meal diet unsupple-

mented with pantothenic acid did not affect their

performance to 21 days of age.


xvi
















CHAPTER I
INTRODUCTION


The discovery of vitamins was a landmark in the history

of nutrition which started between 1897, with the finding by

Eijman in Java (reviewed by Leicester, 1956) of what later

was shown to be thiamin, and 1912 when Funk (Leicester,

1956) and Hopkins (1912) formulated the concept of vitamin.

This period of vitamin discoveries ended in 1948 with the

isolation of vitamin B12 by Smith in England and Rickes and

Folkers in the United States (Scott et al., 1982).

The chicken (Gallus domesticus) has played an

important role as an experimental animal in the discovery,

isolation and identification of most of the vitamins. In

fact, by the time the first revision of the Recommended

Nutrient Allowances for Poultry (NRC, 1946) was published,

allowances for vitamin A, vitamin D, thiamin, riboflavin,

pantothenic acid, niacin, pyridoxine, biotin and choline

for the starting chick were already suggested. However,

since "all things change, and nothing remains at rest" as

the old Greek thinker Heraklitos used to teach (Allen,

1966), a re-evaluation of the requirement of some B-complex

vitamins for the starting chick and turkey poult was deemed

necessary. At least four important factors seem to indicate










that new research in relation to vitamin requirements of

poultry is needed.

First, chickens and turkeys are not the same today as

30 or 40 years ago. That is, the requirement for a given

vitamin could be modified in new strains of birds.

Cultivars of cereal grains, soybeans, cottonseed and other

feedstuffs are not the same either. Thus, it is possible

that the bioavailability of some vitamins and other

nutrients has been changed as a consequence of genetic

crosses.

Second, although it is still possible to assert that in

general synthetic vitamins are not expensive, the fact that

poultry integrated companies are tending to be much larger

implies that a few pennies per ton of feed spent in excess

vitamin supplementation may become thousands of dollars on a

yearly basis.

Third, given the fact that the strains of chicks and

poults used 30 or 40 years ago grew at lower rates than

modern strains, the extent and severity of a specific

vitamin deficiency could be aggravated as a consequence of

a greater requirement of a vitamin per unit of body gain.

Fourth, various vitamins as well as mineral require-

ments were established using small groups of birds and

purified or semipurified diets. Therefore, the main objec-

tive of the research presented in this dissertation was to

re-evaluate the niacin and riboflavin requirements of










broiler chickens and the niacin, riboflavin and pantothenic

acid requirements of turkey poults.

An essential aspect associated with the objective was

that the vitamin requirements were to be studied using a

practical diet. The reason for this was to obtain data

which had confronted some of the actual limitations of this

type of diet. It is well known, for instance, that various

vitamins and minerals, particularly in intact vegetable

ingredients, are only partially bioavailable for the

monogastric animal. However, the main problem is not that

a fraction of a given vitamin is unavailable but the

uncertainty and variability of the amount that eventually

is utilized by the animal. Carter and Carpenter (1982)

demonstrated that the bioavailable niacin in foods is not

just the "free niacin" (i.e., the nicotinic acid and

niacinamide) but also a fraction of the "bound" niacin

which was assumed in the past to be totally unavailable.

Therefore, typical yellow corn-soybean meal diets which are

commonly used by the poultry industry in the United States

were used.

Current knowledge on the biochemical role of niacin,

riboflavin and pantothenic acid is their function in the

coenzymes nicotinamide adenine dinucleotide (NAD), flavin

adenine dinucleotide (FAD), and coenzyme A, respectively

(Cory, 1986; Lehninger, 1975). However, their relevance

in the nutrition of higher animals is their dietary

essentiality. The following paragraphs refer to a brief










description of NAD, FAD and coenzyme A, according to current

knowledge in biochemistry taken from Cory (1986) and

Lehninger (1975) with some specific references to avian

species.

NAD is synthesized in mammalian and avian cells by at

least three different pathways. First, tryptophan can be

metabolized to quinolinic acid which in turn is utilized in

a reaction with phosphoribosyl pyrophosphate to form

nicotinate mononucleotide (de novo synthesis of NAD). A

second pathway is when dietary nicotinic acid reacts with

phosphoribosyl pyrophosphate to form nicotinate

mononucleotide. The enzyme catalyzing this reaction is

nicotinate phosphoribosyltransferase and is widely

distributed in various tissues. Nicotinate mononucleotide

reacts with ATP to yield nicotinate adenine dinucleotide

(also called deamido-NAD). The enzyme catalyzing this

reaction is NAD-pyrophosphorylase and is widely distributed

in various tissues. Deamido-NAD reacts with glutamine with

the hydrolysis of ATP to yield nicotinamide adenine

dinucleotide (NAD).

Third, nicotinamide reacts with phosphoribosyl pyro-

phosphate to give nicotinamide mononucleotide (NMN). The

enzyme which catalyzes this reaction is the same enzyme that

catalyzes the reaction between nicotinate mononucleotide and

ATP.

Nicotinamide phosphoribosyltransferase appears to be

the regulated enzyme in NAD synethsis. NMN, NAD, NADP and










NADPH are strong inhibitors of NMN synthesis. The intra-

cellular concentration of pyridine nucleotides is maintained

at a constant level, implying a pathway that is tightly

regulated. This is very important in dealing with a niacin

deficiency because the NAD concentration in the liver, even

when there is no niacin in the diet, remains constant. The

latter has been observed in rats (Morrison et al., 1963), in

chickens (Childs et al., 1952) and in quails (Park and

Marquardt, 1982a). However, Park and Marquardt (1982b)

demonstrated that breast muscle level is markedly affected

by niacin status whereas liver level is not affected.

The conversion of tryptophan to niacin, which has been

referred above as the de novo synthesis of NAD, is also

called the kynurenine pathway. In this pathway tryptophan

is metabolized to quinolinic acid. The latter is utilized

in a reaction with phosphoribosyl pyrophosphate to form

nicotinate mononucleotide (Gholson, 1966). The enzyme

catalyzing this reaction, quinolinate phosphoribosyl-

transferase, is found only in the liver and kidney (Ikeda

et al., 1965) and, therefore, it is the reason for the

specificity of this pathway for these tissues.

The same year that Krehl et al. (1945) discovered the

interrelationship between tryptophan and niacin, Briggs

(1945) demonstrated that such an interrelationship was also

present in the chick. Thereafter, Furman et al. (1947)

found the existence of the conversion of tryptophan to

niacin in the developing turkey embryo, and Schweigert









et al. (1948) found the same in the developing chick embryo.

The contribution of the last two papers was of great

significance in understanding that cells of higher animals

were capable of operating on the entire chain of reactions

from tryptophan to niacin. It was thought at that time that

animal tissues had only the enzymes necessary to transform

tryptophan into quinolinic acid. The conversion of

quinolinic acid to nicotinic acid was attributed to the

intestinal microflora (Quagliariello, 1963).

A detailed description of the kynurenine pathway is not

normally found in textbooks of biochemistry. However, among

several literature reviews those of Quagliariello (1963) and

DiLorenzo (1972) are very instructive.

Excretion of nicotinamide in urine varies with species.

In humans nicotinamide is excreted as N'-methylnicotinamide

and 2-pyridone-5-carboxamide (Cory, 1986). In chickens,

however, it is excreted as dinicotinyl ornithine (Dann and

Huff, 1947).

In relation to the flavin adenine dinucleotide, FAD,

for which riboflavin is required, its synthesis involves a

two-step reaction. Riboflavin is phosphorylated by ATP in a

reaction catalyzed by riboflavin kinase to give riboflavin

phosphate. The latter reacts with ATP to yield FAD in a

reaction catalyzed by FAD pyrophosphorylase (Cory, 1986).

The vitamin content of milk was instrumental not

only in the formulation of the concept of the vitamin in

general (Hopkins, 1912) but in the discovery of riboflavin










in particular. Norris et al. (1930) were the first to

report the signs of riboflavin deficiency in chickens

(when it was unknown that riboflavin was involved) using a

milk vitamin concentrate. By 1936, Norris et al. (1936)

published the first estimation of the riboflavin require-

ment of chickens. Phillips and Engel (1938) described the

histopathology of riboflavin deficiency in chickens.

Relatively little research has been conducted on the

riboflavin deficiency in chickens and turkeys after its

dietary essentiality was established. Gries and Scott

(1972) did not find the sciatic nerve lessons in

riboflavin-deficient chicks described by Phillips and Engel

(1938). But Jortner et al. (1985) reported that the sciatic

nerve of riboflavin-deficient birds had a demyelinating

neuropathy at 15 days of age. Chou (1971) studied the

effect of riboflavin deficiency on the metabolism of

oxypurines in chicks. Oxypurine metabolism was distributed

in riboflavin-deficient birds in both the liver and the

kidney as measured by the accumulation of total oxypurines

(hypoxanthine, xanthine and uric acid). Chou (1971) con-

cluded that the incorporation of dietary riboflavin into

xanthine dehydrogenase is essential for oxypruine

metabolism. Chou et al. (1971) found that in severe

riboflavin deficiency in broiler chicks, the efficiencies

of utilization of both energy and protein were decreased

significantly. However, the efficiency of energy









utilization but not of protein was decreased significantly

in border-line riboflavin deficiency.

Coenzyme A is assembled, starting from the free

vitamin pantothenic acid, in a reaction sequence involving

at least five metabolic steps. Pantothenic acid is phos-

porylated by ATP to give 4-phosphopantothenic acid.

In the next reaction cysteine is added to provide the -SH

group, which will be ultimately the active end of coenzyme

A. The alpha carboxyl group of cysteine is then removed

from 4-phosphopantothenoyl-L-cysteine to yield

4-phosphopantothine. In a pyrophsophorylase reaction, ATP

is then added to give dephosphocoenzyme A. The dephospho-

coenzyme A is then phosphorylated at the 3' position of the

adenosine moiety to give coenzyme A (Cory, 1986; Lehninger,

1975).

The pyridine nucleotides function as the coenzymes of

a large number of oxidoreductases collectively called

pyridine-linked dehydrogenases. They act as electron

acceptors during the enzymatic removal of hydrogen atoms

from specific substrate molecules. The flavin nucleotides

function as prosthetic groups of oxidation-reduction enzymes

known as flavoenzymes or flavoproteins. These enzymes

function in the oxidative degradation of pyruvate, fatty

acids and amino acids, and also in the process of electron

transport. The function of coenzyme A is to serve as a

carrier of acyl groups in enzymatic reactions involved in









fatty acid oxidation, fatty acid synthesis, pyruvate

oxidation and biological acetylations (Lehninger, 1975).

The dynamic and interrelated role of the coenzymes

containing niacin, riboflavin and pantothenic acid in energy

metabolism is clearly seen in the oxidation of pyruvate to

acetylcoenzyme A. This reaction, which is irreversible in

animal tissues, is not itself part of the Krebs cycle but is

obligatory for the entry of all carbohydrates (via pyruvate)

into the Krebs cycle.

The literature review on the requirement of each

specific vitamin (niacin, riboflavin or pantothenic acid)

will be integrated in the discussion of the results obtained

in each set of experiments for a specific vitamin study with

chicks or poults.
















CHAPTER II
NIACIN STUDIES WITH BROILER CHICKENS


The Niacin Requirement of Broiler Chickens
Fed a Corn-Soybean Meal Diet from One
to Twenty-One Days of Age


Introduction


The essentiality of niacin for the chicken was

established for the first time by Briggs et al. (1942,

1943). They found that approximately 18 mg of niacin per kg

of purified diet were adequate to prevent poor growth, chick

blacktongue and occasional perosis or scaly dermatitis.

Childs et al. (1952) concluded, from four experiments

with corn-soybean meal diets, that the niacin requirement of

chickens 1 to 8 weeks of age was between 26 and 28 mg per kg

of feed. West et al. (1952) working under similar condi-

tions as Childs et al. (1952), but with a purified diet,

found that 30 mg of niacin per kg were required. The

tryptophan requirement was adequately met when the diet

contained .19% of tryptophan. Patterson et al. (1956),

feeding a semipurified diet to chicks up to 4 weeks,

reported that optimum growth was obtained either with 17 to

20 mg of niacin per kg in the presence of .24% tryptophan,

or with 28 to 33 mg of niacin per kg and .14% tryptophan.

On the other hand, Fisher et al. (1955) using a purified










diet determined the tryptophan requirement to be .15% in the

presence of adequate niacin. At this minimum level of

tryptophan the dietary niacin requirement was reported to

vary from 25 to 100 mg per kg of diet depending on certain

stress conditions such as dietary amino acid imbalances.

The National Research Council has suggested a require-

ment of 27 mg of niacin per kg of feed for chickens 0 to 8

weeks of age since 1966 (Titus and Fritz, 1971). This

value, which is essentially the same as that reported by

Childs et al. (1952), has been questioned. Yoshida et al.

(1966) working with a purified diet containing approximately

.9 mg of niacin per kg, found that the dietary requirement

of meat-type crossbred chicks was 37 mg per kg and 7.2 mg

per kg for egg-type chicks. Waldroup et al. (1985) con-

ducted studies with corn-soybean meal diets containing at

least 54 mg niacin per kg of feed (20.7 mg calculated from

intact ingredients plus 33 mg added niacin in the vitamin

premix); a significant increase in body weights was obtained

at 49 and 53 days of age when supplemented with either 33,

66 or 99 mg of niacinamide per kg of feed. These authors

concluded that the modern, rapidly growing broiler chick

may require niacin levels greater than those currently

recommended by the NRC (1984).

As a consequence of the aforementioned conflicting

reports on the niacin requirement of broiler chickens, and

taking into consideration (as suggested by Waldroup et al.,

1985) that most of the research on this subject was










conducted approximately 30 years ago when broiler chickens

grew at slower rates than modern strains, it was deemed

necessary to re-investigate the niacin requirement of

broiler chickens fed corn-soybean meal diets. The purpose

of this section is to report results concerning studies con-

ducted with birds from day-old to 21 days of age. The next

section will deal with results obtained from 3 to 7 weeks of

age.


Materials and Methods


Four experiments were conducted using a total of 1408

day-old broiler chicks. In the first experiment Cobb x

Arbor Acres chicks were used while in the other three

experiments the chicks used were Cobb x Cobb. In each

experiment birds were housed for 21 days in Petersime

battery brooders. Eight birds per pen, four male and four

female chicks, were used per replicate. Feed and water were

offered ad libitum. The composition of the corn-soybean

meal basal diet was essentially the same in all four

experiments (Table 2-1). The vitamin premix was formulated

to be devoid of niacin. Since the experiments were con-

ducted between July 1985 and February 1986, the corn, the

soybean meal, and the animal fat used to mix the basal diets

did not come necessarily from the same lots; therefore, the

basal diet for each experiment was analyzed separately

(Table 2-1). Crude protein, moisture, and ether extract

analyses were conducted on the diets according to the



























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methods of the Association of Official Analytical Chemists

(AOAC, 1984). Tryptophan and niacin contents were deter-

mined by different laboratories* on subsamples of a

homogeneous total sample. Tryptophan was analyzed by the

method of Whitacre et al. (1986), and niacin according to

the colorimetric and microbiological methods of the AOAC

(1984). The average of both analyses was used as the

analyzed niacin value. A niacin supplement (99.5% purity)

from the same production lot** was used throughout all the

experiments.


Experiment 1. Three hundred eighty-four broiler

chicks were assigned to six dietary treatments 0, 3, 6, 12,

33, and 66 mg of supplemental niacin per kg of feed with

eight replicates per treatment.


Experiment 2. Two hundred eighty-eight broiler

chicks were assigned to the six dietary treatments as

described in Experiment 1 with six replicates per treatment.


Experiment 3. Four hundred broiler chicks were

assigned to five dietary treatments 0, 3, 6, 12, and 15 mg


*Tryptophan analysis, courtesy of Degussa Corporation,
Teterboro, New Jersey. Niacin analyses, Barrow-Agee
Laboratories, Memphis, Tennessee colorimetricc method);
Hazelton Laboratories America, Inc., Chemical & BioMedical
Sciences Division, Madison, Wisconsin (microbiological
method).

**Niacin, Animal Nutrition Feed Grade min. 99.5%, Lonza,
Inc., Fair Lawn, New Jersey.










of supplemental niacin per kg of feed with 10 replicates per

treatment.


Experiment 4. Three hundred thirty-six broiler

chicks were assigned to seven dietary treatments 0, 3, 6,

12, 33, 66, and 132 mg of supplemental niacin per kg of

feed. Each diet was fed to six replicates per treatment.

At 21 days of age, male and female birds were weighed

on a per pen basis, each individual bird was visually

evaluated for leg disorders, and feed consumption was

determined by pen.

In order to fit the broken-line linear model the

non-linear regression procedure of SAS (1985) was applied to

the growth data of each experiment. This procedure provided

the equation of the ascending line, and the average value at

which plateau for body weight occurred when the minimum

residual sum of squares was obtained. The minimum require-

ment for growth was estimated as the intersection of the

ascending line and the plateau.


Results and Discussion


In all four experiments birds fed the corn-soybean meal

basal diet without supplemental niacin to 21 days of age

were depressed in growth and exhibited leg abnormalities,

primarily bowed legs. Conversely, increased niacin supple-

mentation resulted in increased body weight until a plateau

was reached. Also, niacin supplementation of the basal









diets not only decreased the number of birds exhibiting leg

disorders but also the severity of the disorder itself. Any

chick having slightly bowed legs was considered to have a

leg disorder. In those treatments in which the leg problem

incidence was approximately 20% or less, the severity of the

condition was observed to be decreased (Tables 2-2, 2-3,

2-4, and 2-5).


Experiment 1. Body weight at 21 days of age reached

a plateau with the addition of 33 mg of niacin per kg of

basal diet (Table 2-2). However, using the broken-line

technique it was calculated that 15 mg of supplemental

niacin per kg of feed were sufficient for this basal diet to

maximize growth (Figure 2-1; Table 2-6). Since the analyzed

niacin content of the basal diet was 25 mg per kg, the

niacin requirement was estimated to be 40 mg per kg of diet.

Feed conversion improved only with a niacin supplemen-

tation level higher than 12 mg per kg of diet, and feed

intake increased in a linear fashion, parallel to growth.

Feed intake plateau was reached at 855 g per bird, while

that for body weight was obtained at 639 g. Therefore, at

the estimated niacin requirement of 40 mg per kg of the diet

the minimum niacin intake of 54 mcg per g of body weight

is required in order to maximize body weight at 21 days.


Experiment 2. Body weight reached plateau with the

addition of 6 mg of niacin per kg of basal diet (Table 2-3).

Only two treatment means fell below the plateau describing a





















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ship between supplemental dietary niacin and
body weight at 21 days of age, Experiment 1

Ascending portion, Y = 541.13 + 6.75 X (plus
sign: predicted equation; square: mean value).
Bar shows standard error of the mean.


















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perfect line for the ascending portion of the plot, body

weight versus supplemental niacin (Figure 2-2; Table 2-6).

Taking into consideration the analyzed niacin content of the

basal diet used in this experiment (Table 2-1), the niacin

requirement was estimated to be 28.5 mg per kg of diet.

Feed conversion was not modified by any dietary treatment.

Feed intake, however, increased in a linear fashion up to

6 mg of supplemental niacin per kg. Feed intake reached a

plateau at 875 g per bird (Table 2-7). Body weight leveled

off at 619 g. Therefore, a minimum niacin intake of 40 mcg

per g of body weight was needed in order to maximize growth

at 21 days.


Experiment 3. In this experiment the highest level

of niacin supplementation used was 15 mg per kg of diet

based on the results obtained with the first two

experiments. The results for dietary treatments in which

6 and 12 mg niacin were added per kg of feed were very

similar (Table 2-4). This factor caused the overall

analysis of results to be less straight forward. However,

the regression analysis of the data indicated an almost

perfect straight line for the first three dietary treatments

(Figure 2-3).

Extrapolation of the intersection of the ascending

portion and the plateau was shown to occur at 7 mg of

supplemental niacin per kg of basal diet (Table 2-6).

Therefore, considering the niacin content of the basal
































Figure 2-2. The broken-line model applied to the relation-
ship between supplemental dietary niacin and
body weight at 21 days of age, Experiment 2

Ascending portion, Y = 573.47 + 7.60 X (plus
sign: predicted equation; square: mean value).
Bar shows standard error of the mean.


























i -- --


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Figure 2-3. The broken-line model applied to the relation-
ship between supplemental dietary niacin and
body weight at 21 days of age, Experiment 3

Ascending portion, Y = 554.48 + 8.86 X (plus
sign: predicted equation; square: mean value).
Bar shows standard error of the mean.





















-------___I
------ ---4.


SUPPLEMENTAL NIACIN MC


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diet (Table 2-1) the requirement was estimated to be 30.5 mg

per kg of the diet. Body weight plateau was reached at

613 g, and that for intake at 865 g (Table 2-7). It was

calculated that in order to maximize body weight at 21 days,

a minimum niacin intake of 43 mcg per g of body weight was

necessary. In this experiment feed conversion improved

linearly as the level of niacin in the diet increased.


Experiment 4. In this experiment the intersection

between the regression line and the plateau was at 8 mg of

supplemental niacin per kg of feed (Figure 2-4; Table 2-6).

Since the analyzed niacin content for the basal diet used in

this experiment was 27.5 mg per kg, a total of 35.5 mg

niacin per kg of feed was required to maximize growth.

Expressing this requirement in terms of mcg of niacin intake

per gram of body weight, 50 mcg were needed (Table 2-7).

Feed conversion was improved linearly up to 12 mg of niacin

supplementation.

It is obvious from the data in Table 2-7 that there

were two different types of responses. In Experiments 2 and

3, 28.5-30.5 mg of niacin were required per kg of feed, and

in Experiments 1 and 4 35.5-40 mg of niacin per kg were

required.

As already mentioned, the experiments were conducted at

different times during an 8-month period, and each basal

diet was mixed a few days before the beginning of each

experiment. Although the yellow corn #2 used in the farm

































Figure 2-4. The broken-line model applied to the relation-
ship between supplemental dietary niacin and
body weight at 21 days of age, Experiment 4

Ascending portion, Y = 496.94 + 12.47 X (plus
sign: predicted equation; square: mean value).
Bar shows standard error of the mean.























/" -
/


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0 3 6 9 12 33 66

SUPPLEMENTAL NIACIN MG










throughout the year came from the same storage location, it

does not mean necessarily that all the grain was grown in

the same field, under the same conditions. However, the

soybean meal used in Experiments 2 and 3 came from the same

bin and the same load. The analyses of the basal diets

(Table 2-1) indicated that they were very similar (despite

1.3% difference in ether extract), and the performance of

birds (Cobb x Cobb from the same broiler breeder flock) was

also very similar as measured by body weight attained at

plateau, amount of supplemental niacin needed to reach such

plateau, mcg intake of niacin and mg intake of tryptophan

per gram of body weight (Table 2-7), and feed efficiencies

(Tables 2-3 and 2-4).

On the other hand, it is apparent that Experiments 1

and 4 were alike in that feed intakes were similar, and

therefore niacin intakes were also similar. The difference

in the gain reached between zero level of niacin supplemen-

tation and the body weight at plateau in each of these two

experiments was almost identical (Table 2-7). However, the

amounts of supplemental niacin needed to maximize body

weight and to improve feed efficiency were different.

Comparison between niacin experiments became further

complicated because of the role of tryptophan intake and its

metabolic conversion into niacin. In Experiments 2 and 3

the tryptophan intake per gram of body weight, with and

without niacin supplementation, was the same in each of

these experiments (Table 2-7). However, in Experiment 2 an









extra intake of .1 mg of tryptophan per gram of body weight

occurred in comparison to Experiment 3. But assuming a

conversion ratio of 54 mg of tryptophan per mg of niacin

(using data presented in the third section of this chapter)

it is possible to calculate that the endogenous niacin,

derived from such extra tryptophan intake in Experiment 2,

was compensated with a similar amount of exogenous niacin in

Experiment 3. Therefore, there were no important differ-

ences between Experiments 2 and 3.

A comparison between Experiment 1 and Experiment 2 in

relation to tryptophan intake per gram of body weight, in

the presence of adequate niacin, indicates an advantage for

Experiment 2 over Experiment 1 (Table 2-7). However, if for

the sake of simplicity, it is assumed that the maximum body

weight attained in both experiments was the same (639 g),

then it is estimated that the extra tryptophan intake in

Experiment 2 (.3 mg per g of body weight) contributed with

approximately 3.5 mg of endogenous niacin (54:1 conversion

ratio). Using the regression equation in Table 2-6 to

extrapolate the supplemental niacin required to reach a body

weight of 639 g in Experiment 2, 8.7 mg of supplemental

niacin per kg of diet would be needed. Therefore, if the

difference between Experiment 1 and Experiment 2 in relation

to the niacin requirement to maximize growth was caused by a

difference in tryptophan intake alone, then approximately

12 mg of niacin per kg of diet were to be sufficient.

However, at least 15 mg of supplemental niacin per kg of










diet were determined to be necessary in Experiment 1 to

maximize the growth of broiler chicks at 21 days of age.

The tryptophan content of the basal diet used in

Experiment 4 was higher than that for any other basal diet

used (Table 2-1). The reason for this was the higher

protein content of this diet. Consequently, the tryptophan

intake in this experiment, even at the zero level of

supplemental niacin, was higher than in the other three

experiments. The analyzed niacin content of the basal diet

was also higher than that for the previous experiments.

Despite these facts, it was determined that at least 8 mg of

supplemental niacin per kg of feed were needed to maximize

growth (Table 2-6). The growth gain and the niacin intake

per gram of body weight were similar for Experiments 1 and 4

(Table 2-7). However, the supplemental niacin needed in

Experiment 1 was greater than in Experiment 4, indicating

the role of the endogenous niacin in the latter.

It is hypothesized, based on the above discussion,

that the difference among these experiments in relation to

the niacin requirement of broiler chicks is related besides

tryptophan intake differences to the amount of bioavailable

niacin in the diet.

The term bioavailability is used here in a way

analogous to that used for other vitamins (Nguyen et al.,

1981), i.e., the fraction of the dietary niacin which is in

a chemical or physical form that is suitable for intestinal

absorption and metabolic utilization. It is well known that










the bound form of niacin is not bioavailable (Kodicek

et al., 1956). Nevertheless, not all bound niacin is

equally or completely biologically unavailable as reported

in detail by Carter and Carpenter (1982). In other words,

it is not just a question of determining the "free niacin"

present in the total niacin in order to quantify the

bioavailable niacin since some bound niacin is also

available.

An indicator, however, that may help to confirm that

differences in bioavailable niacin were involved in the

variation observed for the niacin requirement of broiler

chicks in these four experiments, is the leg disorder

incidence. Although the evaluation of leg abnormalities is

somewhat subjective (particularly in borderline situations

when the disorder is very slight), the leg disorder inci-

dence at the zero level of niacin supplementation, along

with the growth and feed intake data at that level, is a

useful tool in comparing the severity of the deficiency

among experiments.

The two highest percentages of leg disorder incidence

occurred in Experiments 1 and 4 along with the lowest body

weights and feed intakes at zero level of niacin

supplementation (Tables 2-2 and 2-5). These experiments

also showed the more severe cases of bowed legs.

Perosis-like abnormalities only occurred in Experiment 4.

In fact, the birds shown in photographs A, B, and C

(Figure 2-5) are from Experiment 1, while a severe case of






















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perosis-like legs (D) is from Experiment 4. In contrast,

birds in Experiments 2 and 3 had the lowest leg disorder

incidence with less severe cases than Experiments 1 and 4.

Body weights and feed intakes for these experiments at zero

supplemental niacin (Tables 2-3 and 2-4) were the highest of

the four experiments. However, the niacin contents for all

these basal diets with only one exception already mentioned

were very similar (Table 2-1). Since these basal diets were

formulated to be deficient only in niacin, it seems reason-

able to attribute the differences in performances of the

birds fed these unsupplemented diets to differences of

bioavailability of the niacin that was present in the intact

ingredients.

The average niacin requirement calculated from the four

experiments (Table 2-6) was 34 mg per kg of the diet with a

standard deviation of 5.2 mg. It is concluded that this

mean value is an adequate estimate of the niacin requirement

of broiler chickens fed a corn-soybean meal practical diet

between 1 and 21 days of age. The conditions under which

this estimate value is suggested need to be emphasized.

First, a modern commercially available strain of

broiler chicks (male and female) was used. If the require-

ment is to be determined with White Leghorn chicks, then it

would be considerably lower as reported by Yoshida et al.

(1966).

Second, birds were housed during the entire experi-

mental period in battery brooders with raised wire floors,










and special care was provided to avoid droppings in the

waterers. Therefore, under practical conditions where

coprophagy is not limited, it is possible that birds ingest

some intact niacin present in the droppings giving the

appearance of a lower requirement.

Third, a practical corn-soybean meal diet formulated to

meet or exceed the nutritional requirements of NRC (1984)

was used. Consequently, the tryptophan contents of the

diets used were typical of a corn-soybean meal diet.

However, as shown in Table 2-1 considerable variation may

occur in the analyzed nutrient content from lot to lot of

feed. Some of the implications of this variability have

been discussed to a certain extent in the above paragraphs.

Fourth, birds were offered the experimental diets

ad libitum from day 1 to day 21. No pre-experimental

period was used, and it is not implied that the suggested

requirement of 34 mg per kg of diet is to be valid after 21

days of age. Furthermore, it is possible that this require-

ment could be reduced before 21 days of age because the

increasing feed intake of the growing chick would eventually

be high enough to allow the bird to satisfy its daily niacin

requirement with what is bioavailable in the unsupplemented

corn-soybean meal diet.

Given the above conditions it is difficult to compare

the suggested estimate of 34 mg of niacin per kg of feed

with previous reported values. Childs et al. (1952)

estimated a requirement of approximately 27 mg per kg









working with corn-soybean meal diets but with birds from

1 to 8 weeks of age reared in battery brooders with wire

floors. West et al. (1952) determined that 30 mg of niacin

per kg were adequate working with the same strain of birds

used by Childs and coworkers (Barred Plymouth Rock) but with

a purified diet and with a different dietary tryptophan

level.

Patterson et al. (1956) reported results of studies on

the niacin and tryptophan requirements of chicks from 1 to

28 days of age, but these researchers used White Leghorn

cockerels and a semipurified diet. Values between 28.0 and

33.0 mg of niacin per kg in the presence of approximately

.14% tryptophan were determined. However, when the same

basal diet was supplemented with .1% DL-tryptophan the

requirement for niacin dropped to approximately 19 mg per

kg.

Yoshida et al. (1966) reported that the niacin require-

ment of broiler chicks (White Cornish x New Hampshire) from

1 to 21 days of age was 37 mg per kg, which is apparently

similar to the 34 mg per kg suggested in the present report.

However, close inspection of their experimental conditions

reveals that they used a highly purified diet (containing

only .9 mg of niacin/kg by microbiological analysis), and

consequently approximately 36 mg of niacin out of the 37 mg

required per kg of diet came from pure niacin. Although

these authors did not mention the tryptophan level of the

diet, it was calculated to be near .20% using NRC (1984)









table values. In contrast, in the experiments reported

here, the average niacin content of the unsupplemented basal

diets was 25 mg per kg (whose bioavailable niacin value is

unknown) and the average supplemental niacin was 9 mg per

kg. At 3 weeks the birds used by Yoshida et al. (1966)

gained 210 g per bird while in these experiments average

gain, for the same period of time, was approximately 570 g.

Yen et al. (1977) concluded that a corn-soybean meal

diet unsupplemented with niacin and fed to growing chicks

under 8 weeks of age did not require niacin supplementation

to maximize growth. But, first the birds were fed adequate

niacin from day 1 to day 7; second, the strain of birds used

was different (New Hampshire males x Columbian females) and

did not grow as fast as a modern commercial broiler strain.

The suggested requirement of 34 mg of niacin per kg of

a practical corn-soybean meal diet fed to broiler chicks

from 1 to 21 days of age is similar to the value of 37 mg

per kg reported by Bao-Ji and Combs (1986) for starting

broilers from 1 to 21 days of age fed a corn-soy-gelatin

diet. However, the suggested requirement of 34 mg per kg is

higher than the current NRC (1984) requirement of 27 mg of

niacin per kg of diet for broiler chickens 0-3 weeks.

Taking into consideration the literature on the subject, it

seems that the current NRC (1984) niacin requirement for

broilers within the age under discussion is based mostly on

studies with broilers 1 to 8 weeks of age.









Waldroup et al. (1985) suggested that levels of niacin

higher than those recommended by NRC (1984) may be required

for optimum growth of broilers to 8 weeks of age. The

levels of supplemental niacin of 33 and 66 mg per kg of diet

used in Experiments 1, 2, and 4 of the present study were

included in order to re-evaluate the suggestion by Waldroup

et al. (1985), since they supplemented those levels to their

corn-soybean meal diets, and reported some response.

However, these authors did not remove the niacin supple-

mented normally in the vitamin premix, and their experiments

were conducted to 53 and 49 days of age. The results

presented here indicate that, at least, from 1 to 21 days

of age the NRC (1984) niacin suggested requirement is lower

than what is found experimentally. Nevertheless, these

results do not seem to support that levels of niacin supple-

mentation as high as 33 or 66 mg of niacin per kg of feed

are required in a corn-soybean meal diet.


Summary


Four experiments were conducted to determine the niacin

requirement of broiler chicks fed a corn-soybean meal diet

from 1 to 21 days of age. A total of 1408 day-old feather-

sexed broiler chicks were used. The unsupplemented corn-

soybean meal basal diet was calculated to contain 21 mg

niacin per kg and .29% tryptophan. However, the basal diet

of each experiment was analyzed for niacin and tryptophan

contents. In Experiment 1, 384 birds were assigned to six









dietary treatments 0, 3, 6, 12, 33, and 66 mg of supple-

mental niacin per kg of diet. In Experiment 2, 288 birds

were assigned to the same treatments as in the first

experiment. In Experiment 3, 400 chicks were assigned to

five dietary treatments 0, 3, 6, 12, and 15 mg of supple-

mental niacin per kg. In Experiment 4, 336 chicks were

assigned to seven dietary treatments 0, 3, 6, 12, 33, 66,

and 132 mg of supplemental niacin per kg of diet. Birds

were weighed at 3 weeks, and feed intake was determined.

At the end of each experiment each bird was evaluated for

leg disorders. Using the broken-line technique, the niacin

requirements for maximum growth from Experiments 1 to 4 were

40, 28.5, 30.5, and 35.5 mg of niacin per kg of feed,

respectively. It is suggested that the average 34 + 5.2

(s.d.) mg of niacin per kg of diet is an adequate estimate

of the niacin requirement of broiler chickens fed corn-

soybean meal practical diets from 1 day to 21 days of age.


The Niacin Requirement of Broiler Chickens
Fed a Corn-Soybean Meal Diet from
Three to Seven Weeks of Age


Introduction


The niacin requirement of broiler chickens has been

reported on the basis of results derived from experiments

conducted either between 1 and 7 to 8 weeks of age (Childs

et al., 1952; West et al., 1952; Yen et al., 1977) or

between 0 and 3 to 4 weeks of age (Patterson et al., 1956;










Yoshida et al., 1966). Sunde (1955) determined the niacin

requirement of chickens from 6 to 11 weeks of age. No

reports are found in the literature in which the niacin

requirement of broiler chickens had been studied considering

the "starter/finisher" feeding system widely used in

industry. Since the niacin requirement of broiler chicks

from 0 to 3 weeks of age using a corn-soybean meal diet was

studied in the first section of this chapter, it was the

objective of this experiment to determine the niacin

requirement of broiler chickens between 3 and 7 weeks of

age.


Materials and Methods


Day-old Cobb feather sexed broiler chicks were grown in

litter floor pens to 3 weeks of age using a corn-soybean

meal diet (Table 2-8) which was formulated to meet or exceed

the nutritional requirements suggested by the National

Research Council (1984). At that age, the number of birds

per pen was adjusted to 18, missexed birds were relocated,

and runts and/or birds with leg problems were culled. Body

weights were determined by pen which were considered the

initial body weights at the beginning of the experiment.

Pens were assigned to six dietary treatments, 0, 3, 6, 12,

24, and 36 mg of supplemental niacin per kg of feed. Six

replicate pens (2.32 m2) of male birds and six replicate

pens of female birds were used for each dietary treatment.








































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The experimental period started January 7 and ended

February 3, 1986. Infrared heat-lamps were used as the

source of heat. Maximum and minimum temperatures inside the

house were recorded daily. The average minimum temperature

during the 28-day period was 13.3 C, and the average maximum

temperature for the same period was 23.30C. Water and feed

were offered ad libitum.

The corn-soybean meal basal diet for the experimental

period (Table 2-8) was formulated to contain 20% crude

protein and 3188 kcal of metabolizable energy per kg of

feed. The microingredient premix was calculated to be

devoid of niacin. Bio-Cox* was used throughout both pre-

experimental and experimental periods. Crude protein,

moisture, and ether extract analyses were conducted

according to the methods of the Association of Official

Analytical Chemists (AOAC, 1984). Tryptophan and niacin

analyses of the basal diet were determined by different

laboratories** on subsamples of a homogeneous total sample.

Tryptophan was analyzed by the method of Whitacre et al.

(1986), and niacin according to the colorimetric and micro-

biological methods of AOAC (1984). The average of both


*Bio-Cox is a registered trademark for salinomycin
sodium (30 g/lb), Agri-Bio Corporation, Gainesville,
Georgia.

**Tryptophan analysis, courtesy of Degussa Corporation,
Teterboro, New Jersey. Niacin analyses, Barrow-Agee
Laboratories, Memphis, Tennessee colorimetricc method);
Hazleton Laboratories America, Inc., Chemical & BioMedical
Sciences Division, Madison, Wisconsin (microbiological
method).









analyses was used as the analyzed niacin value. Niacin feed

grade (99.5% purity)* was used as a source of supplemental

niacin.

When the birds were 7 weeks old, body weights were

obtained by pen, and body weight gains were determined.

Feed intake was determined also on a per pen basis. Gain,

feed intake, and feed conversion data were subjected to the

analysis of variance (SAS, 1985).


Results and Discussion


There were no significant differences in body weight

gain (P = .67), feed intake (P = .36), and feed conversion

(P = .12) due to dietary treatments (Table 2-9). Since the

treatment x sex interactions were not significant for gain

(P = .53), feed intake (P = .76) and feed conversion (P =

.53), the data for both sexes were combined for presentation

(Table 2-9).

These data indicate that the niacin content of a corn-

soybean meal diet, such as that used in this experiment (the

analyzed niacin content was 22 mg per kg) at the typical

intakes observed (Table 2-9), is enough to meet the require-

ment of this vitamin between 3 and 7 weeks of age. It was

concluded, in the first section of this chapter, that a

total of 34 mg of niacin per kg of feed was adequate for

maximum growth of broiler chicks to 21 days of age.


*Niacin, Animal Nutrition Feed Grade min. 99.5%, Lonza,
Inc., Fair Lawn, New Jersey.






















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The average number of mcg of niacin intake per gram of body

weight, calculated from four experiments to maximize growth

at 21 days, was approximately 47 mcg.

In this experiment, for the pre-experimental period,

the overall average body weight at 3 weeks was 554 g + 4.9

(mean + SEM) with an overall average feed intake per bird

of 850 g + 19.5. If the dietary niacin were at the

minimum estimated requirement of 34 mg per kg of feed (the

actual niacin supplementation for the pre-experimental diet

was higher than the minimum requirement), then an intake of

29 mg per 554 g of body weight resulted, or approximately 52

mcg of niacin intake per gram of body weight. Conversely,

the average body weight gain between 3 and 7 weeks at the

zero level of niacin supplementation (Table 2-9) was 1645 g,

and the average feed intake over the same period of time for

the same dietary treatment was 3527 g. Since the analyzed

niacin content of the basal diet was 22 mg per kg, an

average niacin intake of approximately 47 mcg per g of body

weight gain occurred.

These average values of niacin intake per gram of body

weight (47, 52, and 47) seem fairly close and allow one to

speculate, contrary to the belief that the niacin require-

ment decreases with age, that probably the niacin require-

ment remains almost constant for boiler chickens from 1 to

49 days of age. However, because feed intake per gram of

body weight increases throughout the same period of time and









since the requirement is expressed in terms of concentration

of the diet, it appears that the requirement decreases.

Whether or not the requirement of a given nutrient

remains constant during growth deserves further research,

but as far as niacin is concerned the problem is particu-

larly complex not only because coprophagy is involved but

also because of the metabolic conversion of tryptophan to

niacin. It is estimated that the tryptophan intake during

the pre-experimental period (0 to 3 weeks) was approximately

3.7 mg per g of body weight which is very similar to the

values observed previously in the first section of this

chapter. From 3 to 7 weeks of age the overall average

tryptophan intake was approximately 5 mg per g of body

weight gain. Although increased growth demands more

tryptophan for protein synthesis, it seems that the

tryptophan content of a typical corn-soybean meal diet is

well above the requirement of broiler chicks (Edmonds

et al., 1985) and consequently, some tryptophan is available

for the kynurenine pathway and eventually for endogenous

niacin synthesis.

The minimum niacin requirement of broiler chickens

between 3 and 7 weeks of age was not determined in this

experiment. The fact that the niacin content of the basal

diet (22 mg per kg) with no supplemental niacin was

sufficient for maximum growth does not necessarily mean that

this was the minimum requirement. However, the average

niacin intake per gram of body weight needed for maximum









growth from 0 to 3 weeks of age (period during which niacin

supplementation to a corn-soybean meal diet was needed) was

essentially the same as that needed for maximum growth from

3 to 7 weeks of age in the absence of supplemental dietary

niacin. This is an indication of the critical interrela-

tionship between the concentration of a nutrient in the diet

and the feed intake by the animal.

Expressing the adequacy of dietary niacin for broiler

chickens from 3 to 7 weeks of age in terms of concentration

of the diet, it is concluded that 22 mg of niacin per kg of

feed are adequate for maximum growth and feed efficiency.

Childs et al. (1952) found 27 mg of niacin per kg of feed

for Barred Plymouth Rock chickens in a corn-soybean meal

diet containing 21 mg niacin per kg of feed. In their

experiments supplemental niacin was needed to reach maximum

growth to 8 weeks of age. Although these authors also

studied the effect of removing niacin from the diet between

3 to 8 weeks of age, they not only removed the supplemental

niacin but most of the dietary niacin by switching the

corn-soybean meal diet for a purified diet. Therefore,

niacin intake was reduced. This was done since they were

interested in determining the accumulation of niacin in the

liver. Unfortunately, no data on feed intake were reported.

Consequently no comparisons can be made.

Sunde (1955) conducted four experiments with birds

(New Hampshire males x White Leghorn females) using a highly

purified diet (1.8 mg niacin per kg). This author concluded









that the dietary niacin requirement of 6 weeks to 11 week-

old chickens was between 7 and 12 mg per kg of feed.

However, Sunde (1955) indicated that data on the avail-

ability of niacin in ingredients for practical diets for

chickens were needed before those results could be applied.

This is of interest because the suggested requirement of

34 mg of niacin per kg of feed from 0 to 3 weeks of age

indicated in the previous section was the average of four

experiments in which one of the variable factors involved

was niacin bioavailability in corn-soybean meal diets.

Therefore, the value of 22 mg niacin per kg suggested for

chickens between 3 and 7 weeks of age could differ due to

variations in niacin bioavailability in the ingredients.


Summary


An experiment involving 1296 Cobb feather sexed broiler

chickens was conducted to determine the need for supple-

mental niacin from 3 to 7 weeks of age when fed a corn-

soybean meal diet. Birds were raised in litter floor pens

to 3 weeks of age with a corn-soybean meal diet that met or

exceeded the NRC (1984) nutritional requirements. From 3 to

7 weeks of age the birds were assigned to six dietary

treatments, 0, 3, 6, 12, 24, and 36 mg of supplemental

niacin per kg of feed. Six replicate pens per sex per

dietary treatment were used. The corn-soybean meal basal

diet (not supplemented with niacin) contained by analysis

21.3% crude protein, .23% tryptophan, and 22 mg of niacin









per kg of feed. Birds were weighed at 3 and 7 weeks of age

on a per pen basis. The body weight gain, total feed

intake, and feed conversion were determined for male and

female chickens between 3 and 7 weeks of age. There were no

significant differences in body weight gain (P = .67), feed

intake (P = .36), and feed conversion (P = .12) due to

dietary treatments. Treatment x sex interactions were not

significant for body weight gain (P = .53), feed intake

(P = .76), and feed conversion (P = .53). It was concluded

that a corn-soybean meal diet containing 22 mg of niacin per

kg was adequate for maximum growth and feed efficiency.


Quantification of the Tryptophan-Niacin
Conversion in Broiler Chicks Fed a
Corn-Soybean Meal Niacin-Deficient Diet


Introduction


Krehl et al. (1945) reported the interrelationship

between tryptophan and niacin in the rat. Very shortly

thereafter, Briggs (1945) demonstrated that such interrela-

tionship was also present in the chick. He reported that

the addition of 10% gelatin to a purified diet low in niacin

caused growth depression and typical niacin deficiency

signs. However, birds fed the basal diet with 10% gelatin

plus either 50 mg of niacin or 2 g of DL-tryptophan per kg

of diet were not depressed in growth, and did not have black

tongue. Fisher et al. (1955) and Patterson et al. (1956)

working with purified and semi-purified diets, respectively,









confirmed the results of Briggs (1945) in relation to the

capacity of tryptophan to completely overcome a niacin

deficiency in the growing chick.

Relatively little research has been conducted on the

quantification of the tryptophan to niacin conversion in the

chicken. Baker et al. (1973) using a purified crystalline

amino acid diet determined a conversion ratio of 45 mg of

tryptophan per mg of niacin. Since the extent to which

tryptophan helps to supply niacin requirements of chickens

under practical conditions has not been accurately

established (Scott et al., 1982), it was deemed of interest

to quantify the conversion of tryptophan to niacin under

these conditions. For this purpose a niacin-deficient corn-

soybean diet was used.


Materials and Methods


Three battery experiments were conducted using a total

of 1632 day-old Cobb x Cobb feather sexed broiler chicks.


Experiment 1. Five hundred twenty-eight birds were

assigned to 11 dietary treatments, 0, 3, 6, 12, and 33

mg of supplemental niacin per kg of diet; 0, 500, 1000, and

2500 mg of supplemental L-tryptophan per kg of diet; three

additional dietary treatments involved 500, 1000, and 2500

mg of supplemental L-tryptophan per kg of diet supple-

mented with 2 mg of pyridoxine per kg of diet.









Experiment 2. Seven hundred twenty chicks were

assigned to nine dietary treatments, 0. 3, 6, 12, and 15 mg

of supplemental niacin per kg of diet; 0, 250, 500, 750, and

1000 mg of L-tryptophan per kg of diet.


Experiment 3. Three hundred eighty-four birds were

assigned to 8 dietary treatments, 0, 3, 6, 12, and 33 mg of

supplemental niacin; 0, 150, 300, and 600 mg of supplemental

L-tryptophan.

In each experiment the basal diet with no supplemental

niacin and no supplemental tryptophan was the common

treatment at zero level of supplementation of each nutrient.

Eight birds (four male and four female chicks) were used per

pen. In Experiments 1 and 3, six replicate pens and in

Experiment 2, 10 replicate pens were used.

The composition of the basal diets was the same in all

three experiments (Table 2-10). However, soybean meal

containing 45% crude protein was used in Experiments 1 and

2, and soybean meal containing 50% crude protein was used in

Experiment 3. The vitamin premix was formulated to be

devoid of niacin. The crude protein (% N x 6.25), moisture,

and ether extract contents of the basal diets were

determined according to the methods of the Association of

Official Analytical Chemists (AOAC, 1984). Tryptophan and



































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niacin contents were determined by different laboratories*

on subsamples of a homogeneous total sample. Tryptophan was

analyzed by the method of Whitacre et al. (1986) and niacin

according the colorimetric and microbiological methods of

the AOAC (1984). The average of both analyses was used as

the analyzed niacin value. A niacin supplement (99.5%

purity) from the same production lot** was used in all three

experiments. Similarly, a L-tryptophan supplement from the

same production lot*** was used in the three experiments.

Pyridoxine was added as pyridoxine hydrochloride.****

In each experiment birds were housed for 21 days in

Petersime battery brooders with raised wire floors. Feed

and tap water were offered ad libitum. At the termination

of each experiment the male and female chicks in each pen

were weighed by group. Feed consumption was determined by

pen.

The slope-ratio procedure (Finney, 1978) was applied to

the relationship between body weight at 21 days of age and


*Tryptophan analysis, courtesy of Degussa Corporation,
Teterboro, New Jersey. Niacin analyses, Barrow-Agee
Laboratories, Memphis, Tennessee colorimetricc method);
Hazleton Laboratories America, Inc., Chemical & BioMedical
Sciences Division, Madison, Wisconsin (microbiological
method).

**Niacin, Animal Nutrition Feed Grade min. 99.5%, Lonza,
Inc., Fair Lawn, New Jersey.

***L-Tryptophan, min. 99%, Degussa Corporation, Chemicals
Division, Teterboro, New Jersey.

****Pyridoxine hydrochloride, Eastman Kodak Co.,
Rochester, New York.









supplemental niacin intake or supplemental tryptophan intake

in each experiment. Only levels of niacin intake or

tryptophan intake in the linear response surface were used

with a common intercept multiple regression model (SAS,

1985). The 95% confidence interval for each ratio was

determined applying Fieller's theorem (Finney, 1978).

Jackknife estimates of the ratio variances (Cochran, 1977)

were used to determine significant differences among the

tryptophan-niacin conversion ratios. The minimum supple-

mental dietary niacin necessary to reach a plateau for body

weight at 21 days of age in each experiment was determined

using the non-linear regression procedure of SAS (1985).


Results and Discussion


Experiment 1. The growth response to the addition of

niacin to the basal diet reached plateau at 6 mg of supple-

mental niacin per kg of diet (Table 2-11). Tryptophan

supplementation of the basal diet resulted in a growth

response which reached plateau at a slightly higher body

weight than that obtained with niacin supplementation (Table

2-12). Each level of supplemental tryptophan was also fed

to the birds with supplemental pyridoxine to assure that

this vitamin was not limiting the tryptophan metabolism

(Lepkovsky et al., 1943; Henderson et al., 1955) since

levels as high as 2500 mg of tryptophan per kg of diet were

supplemented. However, a t-test for each pair of body

weight means (trytophan vs tryptophan plus pyridoxine) was








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not significant (P > .05). These results indicate that

the vitamin B6 content of a typical corn-soybean meal diet

for broiler chickens at the feed intakes observed in this

experiment is adequate for maximum growth at 3 weeks of age.

Therefore, the results for growth, feed intake, and feed

conversion for the tryptophan dietary treatments were

combined with those for the tryptophan plus pyridoxine

dietary treatments (Table 2-13).

The slope-ratio technique for this experiment indicated

a conversion ratio of tryptophan to niacin of 164:1 (Table

2-18, Figure 2-6). The 95% confidence interval for this

ratio as calculated by the Fieller's theorem was 103.5 -

257.8 (Table 2-19).


Experiment 2. Using non-linear regression analysis

of the growth data, the plateau for body weight was reached

at approximately 7 mg of supplemental niacin (the average

+ SEM body weight for 12 and 15 mg of supplemental niacin

per kg of diet was 613 + 6.7 g; Table 2-14). Supplemental

tryptophan at the level of 250 mg per kg of diet was almost

enough to maximize the body weight of birds at 21 days of

age. The addition of 500 mg of tryptophan per kg of diet

resulted only in a 9 gram increase over the body weight

attained with 250 mg of supplemental tryptophan per kg

of diet (Table 2-15). No further response to higher levels

of tryptophan was observed.





















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Figure 2-6. Regression of body weight of broiler chicks
at 21 days of age on niacin intake (X1) and
tryptophan intake (X2), Experiment 1

Y = 574 + .054 X1 + 8.91 X2 (plus sign:
tryptophan intake per pen; square: niacin
intake per pen; diamond: predicted equation).































TRYPTOPHAN


NIACIN
a
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NUTRIENT INTAKE MG





















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Using the slope-ratio technique, the data for this

experiment suggested a conversion ratio of approximately

50 mg of supplemental tryptophan ingested to 1 mg of niacin

(Table 2-18, Figure 2-7). The 95% confidence interval was

32.2 80.7 (Table 2-19).


Experiment 3. Maximum body weight of the birds at

3 weeks of age was attained at approximately 600 g in this

experiment (Table 2-16). Non-linear regression analysis

indicated that a minimum of approximately 8 mg of supple-

mental niacin per kg of diet was necessary to maximize

growth. Supplemental tryptophan promoted growth in a

similar fashion as supplemental niacin did (Table 2-17). In

this experiment, in contrast to Experiments 1 and 2, feed

conversion was significantly better when either supplemental

niacin or supplemental tryptophan was present in the diet

than at the zero level of supplementation.

The tryptophan-niacin conversion ratio in this experi-

ment, as estimated by the slope-ratio technique, was found

to be 57:1 (Table 2-18, Figure 2-8). The 95% confidence

interval for this ratio was calculated to be 45.7 73.0

(Table 2-19).

As expected, tryptophan supplementation of a niacin-

deficient diet resulted in the prevention of the niacin

deficiency signs observed in chickens, such as poor growth

and bowed legs. However, the quantitative data of the

metabolic conversion of tryptophan to niacin are the first




































Figure 2-7. Regression of body weight of broiler chicks
at 21 days of age on niacin intake (Xj) and
tryptophan intake (X2), Experiment 2

Y = 553 + .218 X1 + 10.84 X2 (plus sign:
tryptophan intake per pen; square: niacin
intake per pen; diamond: predicted equation).


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Figure 2-8. Regression of body weight of broiler chicks
at 21 days of age on niacin intake (XI) and
tryptophan intake (X2), Experiment 3

Y = 497 + .196 X1 + 11.24 X2 (plus sign:
tryptophan intake per pen; square: niacin
intake per pen; diamond: predicted equation).



















640

630 o

620 o

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reported in chickens using a complete practical diet. The

conversion ratios determined in either Experiments 2 and 3

were similar although they were higher than that reported by

Baker et al. (1973) using a purified crystalline amino acid

diet. These authors determined, on a weight basis, a con-

version of supplemental tryptophan to niacin of 45:1 in the

absence of dietary niacin, and a minimum dietary tryptophan

of 1300 mg per kg of diet.

The tryptophan-niacin conversion ratio determined in

Experiment 1 (R1, 164:1) was considerably higher than those

determined in Experiments 2 and 3 (R2, 50:1, and R3, 57:1,

respectively, Table 2-19). Multivariate methods were used

with the jackknife estimated ratio variances to test the

null hypothesis (R1 = R2 = R3) which was rejected at P <

.01. The same multivariate method was used to test

significant differences between the ratios. R1 was

significantly different than R2 and R3 (P < .01). However,

R2 and R3 were not significantly different (P > .01). The

95% C.I. for R1 was considerably wider than that for R2 and

R3 but it did not overlap with the confidence intervals of

the latter (Table 2-19). This fact further confirmed that

R1 was different than R2 and R3. The C.I. for R2 and R3

were relatively similar although that for R3 was contained

within the C.I. for R2.

Despite the fact that there was a clear statistical

difference between the tryptophan-niacin conversion ratio

for Experiment 1 and those found for Experiments 2 and 3, a









biological explanation for this difference is not that

clear.

Tryptophan-niacin conversion ratios, in chickens,

higher than 45:1 or 60:1 have been previously computed. Yen

et al. (1977) indicated that conversion factors as high as

188:1 were calculated in experiments with chicks, when

different levels of various preparations of soybean meals

were introduced in a purified crystalline amino acid diet

devoid of niacin. These authors could not find a reasonable

explanation for such high conversion factors. However,

inspection of their tabulated data from two experiments

indicate that supplemental levels of less than 10% of either

soybean meals or autoclaved fullfat soybeans resulted in

tryptophan-niacin conversion ratios between 47:1 and 99:1,

being the average approximately 63:1. But supplemental

levels of the aforementioned ingredients at 10% and at 20%,

consistently resulted in conversion ratios between 139:1 and

188:1 being always higher at the 20% level of ingredient

supplementation. Manoukas et al. (1968) estimated a conver-

sion ratio of tryptophan to niacin in White Leghorn hens of

187:1 based on available niacin and tryptophan intakes, and

percent hatchability. They used yellow corn-semipurified

diets.

When tryptophan-niacin conversion ratios are compared

or discussed, it is important to consider the basis on which

the conversion ratio was computed. For instance, Fisher

et al. (1955) indicated that in their studies a conversion









ratio of approximately 20:1 occurred, based on chick growth

at 3 weeks of age and dietary concentrations of tryptophan

and niacin. Therefore, the effect of feed intake was not

factored out. Similarly, DiLorenzo (1972) reported differ-

ences in the conversion ratios of tryptophan to niacin in

two strains of chickens based also on growth data and

dietary concentrations of supplemental tryptophan and

niacin. However, his tabulated data suggest that large

differences in feed intake occurred between the two strains

and computation of the conversion factors considering feed

intake decreases the difference between the conversion

factors of the two strains.

The tryptophan-niacin pathway which occurs in liver and

kidney tissues only (Ikeda et al., 1965) functions between

very definite lower and upper steady-state limits which,

however, vary from organism to organism (Arcos and Argus,

1974). Most research has been conducted with mammals,

particularly humans and rats. However, it is assumed that

most of the findings in relation to those factors affecting

the quantitative conversion of tryptophan to niacin are also

valid for avian species.

Among the several factors affecting the efficiency

of the conversion of tryptophan to niacin, hormones

(Mehler et al., 1958; Wolf, 1971; Bender and Totoe, 1984)

and dietary factors such as protein level (Satyanarayana

and Rao, 1977), tryptophan and niacin intakes (Nakagawa

et al., 1973) have been suggested to be involved.









Therefore, several possibilities would eventually help to

explain why the tryptophan-niacin conversion factor of 164:1

was determined in Experiment 1 in contrast to conversion

factors close to 50 to 57:1 as determined in Experiments 2

and 3.

One of the key enzymes that has been suggested as being

involved in the regulation of the tryptophan-niacin pathway

is picolinic acid carboxylase (Ikeda et al., 1965).

Although no enzyme activities were determined in the livers

or kidneys of birds in these experiments, it is possible to

think that picolinic acid carboxylase (PAC) activity did not

play a role in determining the difference in the efficien-

cies of the conversion of tryptophan to niacin observed

between Experiment 1 and Experiments 2 and 3.

The above hypothesis is based, first, on the fact that

differences in PAC activity have been associated with

genetic or strain differences (Ikeda et al., 1965;

DiLorenzo, 1972). The broiler chicks used in the three

experiments under discussion were from the same strain

(Cobb x Cobb), and they were hatched from the same flock of

broiler breeders.

Second, on the data of Penz et al. (1984) who conducted

battery experimetns with broiler chicks using a purified

diet marginal in thyptophan and deficient in niacin. In

their experiment additions of 2000 mg of tryptophan or 60 mg

of niacin per kg of diet improved growth and reduced

perosis. However, the liver PAC activity was not modified









in spite of the relatively large intakes of either

tryptophan or niacin. The PAC activity in the kidney

did change with supplemental tryptophan or niacin.

Nevertheless, the efficiency of the conversion of tryptophan

to niacin was constant independently of the kidney PAC

activity. Penz et al. (1984) did not compute the conversion

factors (it was not their objective), but their tabulated

data permitted this calculation. A conversion ratio of

approximately 32-35:1 occurred in their experiment in which

kidney and liver in vitro PAC activities were measured.

The PAC activity has been related to the efficiency

of conversion of tryptophan to niacin when in vitro deter-

minations have been taken into consideration. In vivo

determinations, however, do not seem to support the same

regulatory function for PAC in the kynurennine pathway.

DiLorenzo (1972) found that the difference in the niacin

requirement between two strains of chickens when fed diets

marginal in tryptophan was related to the different ability

between both strains to convert tryptophan to niacin.

DiLorenzo (1972) found also that the two strains differed in

their in vitro PAC activities. However, this author was not

able to confirm the difference in activity of PAC between

both strains in vivo. Similar results have been reported

in the case of the cat; that is, the extremely high in vitro

PAC activity in the feline liver (as compared with that of

the rat; Ikeda et al., 1965) has not been detected in vivo

(Suhadolnik et al., 1957; Leklem et al., 1971).









The possibility that the tryptophan-niacin conversion

ratio of 164:1 calculated in Experiment 1 was an experi-

mental artifact cannot be ruled out. It is known that

tryptophan pyrrolase, which catalyzes the first step in the

kynurenine pathway, can be inhibited by several factors.

One of such factors is NADPH (the reduced form of

nicotinamide adenine dinucleotide phosphate), that is, the

ultimate distal product in the conversion of tryptophan to

niacin (Cho and Pitot, 1968). Therefore, the dietary level

of niacin, depending on its bioavailability may play a

role in the actual amount of tryptophan that enters the

kynurenine pathway (Dickerson and Wiryanti, 1978).

The calculation of the conversion ratio using the

slope-ratio technique takes into consideration the

tryptophan and niacin intakes which yield a similar growth

during the same period of time. Increased available

tryptophan for catabolism by the kynurenine pathway (as a

consequence of increased tryptophan ingestion and

absorption, for instance) results in more synthesis of

tryptophan pyrrolase (Cho and Pitot, 1968). However, it

would be expected that after a certain level of endogenous

niacin is reached, the negative feedback mechanism would

control the amount of tryptophan entering the pathway.

Consequently, it is plausible that a fraction of the

tryptophan ingested and absorbed would not enter the

kynurenine pathway. Such tryptophan fraction would be

excreted in the urine unmetabolized as it has been observed









in other species (Leklem et al., 1969). However, since the

calculation of the conversion ratio is based on tryptophan

intake, the conversion ratio would become artificially

inflated indicating a lower efficiency than what in reality

occurred.

The chemical analyses for the basal diets for Experi-

ments 1 and 2 (Table 2-10) indicated that these diets were

very similar. The performance of the birds of both experi-

ments was also similar when the plateau for body weight was

reached with niacin supplementation (Table 2-20). The

maximum body weight attained with tryptophan supplementation

was higher for Experiment 1 than for Experiment 2. The

total niacin needed, however, to maximize growth was almost

identical as well as the niacin intake per g of body weight.

Therefore, the large difference between these two experi-

ments in relation to the tryptophan to niacin conversion

(164:1 vs 50:1) seems to be related to the fact that higher

levels of tryptophan were used in Experiment 1 than in

Experiment 2, leading to the calculation of an inflated

conversion ratio in Experiment 1 as hypothesized above.

The chemical composition of the basal diet used in

Experiment 3 indicates that it was higher in tryptophan and

niacin (Table 2-10). However, the supplemental niacin

needed to reach a plateau for body weight as well as the

growth depression at the zero level of either niacin or

tryptophan supplementation (Table 2-20), suggest that

probably niacin was less available in this diet.




















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