• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Introduction
 Phosphorus requirements
 Phosphorus sources and availab...
 Phosphorus absorption
 Phosphorus and milk fever
 Research to reduce excretion
 Okeechobee field trial
 Intake and excretion
 Formulating rations
 Summary
 Selected references
 Back Cover






Group Title: Florida Cooperative Extension Service circular 849
Title: Phosphorus nutrition and excretion by dairy animals
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00049223/00001
 Material Information
Title: Phosphorus nutrition and excretion by dairy animals
Series Title: Circular
Physical Description: 9 p. : ill. ; 28 cm.
Language: English
Creator: Harris, Barney
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1990?
 Subjects
Subject: Dairy cattle -- Feeding and feeds   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 9).
Statement of Responsibility: B. Harris ... et al..
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00049223
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 21500798

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page i
    Introduction
        Page 1
    Phosphorus requirements
        Page 1
    Phosphorus sources and availability
        Page 2
    Phosphorus absorption
        Page 3
    Phosphorus and milk fever
        Page 4
    Research to reduce excretion
        Page 5
    Okeechobee field trial
        Page 5
    Intake and excretion
        Page 6
    Formulating rations
        Page 6
        Page 7
        Page 8
    Summary
        Page 9
    Selected references
        Page 9
    Back Cover
        Page 10
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida




0 3 d_


CiP. 849


Phosphorus
Nutrition
and
Central Science Excretion
Library Excretion
MAY 29 1990 by
Lj U:.;ersity of Florida D
-Dairy
Animals


B. Harris, Jr., D. Morse, H.H. Head and H.H. Van Horn*


Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean










Phosphorus Nutrition and Excretion by


Dairy Animals




B. Harris, Jr., D. Morse, H.H. Head, and H.H. Van Horn*


Introduction
Phosphorus plays a major role in the structure and
function of living cells. It is an integral component
of nucleic acids, nucleotides, phospholipids, and
proteins, and a key component of many coenzymes.
These compounds function in cellular division and
growth, in the transport and metabolism of fats, and
in the absorption and utilization of carbohydrates,
fatty acids, and proteins.
Parturient paresis or milk fever can be a problem
in dairy herds when rations contain less than needed
amounts of phosphorus. The phosphorus content of
plasma and serum, however, decreases with a chronic
or a prolonged deficiency even though the content in
milk does not decrease. Phosphorus in bone is
mobilized to some extent to maintain normal con-
centration in blood but at a slow rate since there is
no direct mobilizing mechanism for phosphorus as
there is for calcium. Since the two elements are
combined in bone, the mobilization of calcium, as a
result of parathyroid gland action, is accompanied by
the incidental mobilization of phosphorus. Animals
with chronic phosphorus deficiency sometimes become
stiff in the joints and in severe cases, are charac-
terized by fragile bones.
About 86% of the phosphorus in cattle is found in
the skeleton and teeth and the remainder in soft
tissues. Bone ash contains about 17% phosphorus.
Blood serum varies in concentration from 3.0 to 8.0
mg of phosphorus/deciliter (dL) (Table 1).
Phosphorus is absorbed in the small intestine as
phosphate. Since phosphorus combines spontaneously
with other elements, it is present in the body in the
phosphate form (PO3). In the bones it occurs as
calcium hydroxyapatite. All cells possess enzymes
that can attach phosphates in ester or acid anhydride
linkages to other molecules. Enzymes exist both


inside and outside of the cells which remove phos-
phates from phosphate-containing molecules.

Table 1. Normal levels of selected minerals in blood serum.
Component Normal Values
(mg/dL)'

Calcium 9-10.6
Magnesium 1-3
Phosphorus 3-8
Potassium 14-20
Sodium 310-340
'dL = 0.1 liter or 100 milliliters.

Phosphorus Requirements
Phosphorus requirements are highest during
lactation, early growth, and for reproduction. High-
producing cows need much more phosphorus than
cows producing at average or low levels. Dry cows or
cows that are not producing milk need less phosphor-
us than lactating cows due to the high content of
phosphorus in milk.
Milk contains about 0.12% calcium and 0.095%
phosphorus. A cow producing 100 pounds of milk
daily would require 100 g (0.220 lb) of phosphorus
and secrete 43 g (0.095 lb) of phosphorus in milk.
Because of the high level of phosphorus in milk, a
continuous supply is needed in the ration in order to
allow high levels of milk production. The amounts of
phosphorus required by dairy cattle, as set forth by
the subcommittee on Dairy Cattle Nutrition of the
National Research Council, are in Tables 2 and 8.
Rations for lactating dairy cattle are formulated to
contain a given quantity or percent of phosphorus in
order to meet the requirements for that specific
nutrient. A lactating dairy cow producing 70 lbs of
milk and consuming 47 lbs of dry matter (DM) daily


B. Harris, Jr. is a Professor and Extension Dairy Specialist with the Dairy Science Department at the Institute of Food and
Agricultural Sciences, University of Florida, Gainesville, FL. D. Morse is an Extension Dairy Specialist at North Dakota State
University in Fargo, N.D. H.H. Head is a Professor in the Dairy Science Department at the University of Florida, Gainesville, FL.
H.H. Van Horn is a Professor and Extension Waste Management Specialist at the University of Florida, Gainesville, FL.










Phosphorus Nutrition and Excretion by


Dairy Animals




B. Harris, Jr., D. Morse, H.H. Head, and H.H. Van Horn*


Introduction
Phosphorus plays a major role in the structure and
function of living cells. It is an integral component
of nucleic acids, nucleotides, phospholipids, and
proteins, and a key component of many coenzymes.
These compounds function in cellular division and
growth, in the transport and metabolism of fats, and
in the absorption and utilization of carbohydrates,
fatty acids, and proteins.
Parturient paresis or milk fever can be a problem
in dairy herds when rations contain less than needed
amounts of phosphorus. The phosphorus content of
plasma and serum, however, decreases with a chronic
or a prolonged deficiency even though the content in
milk does not decrease. Phosphorus in bone is
mobilized to some extent to maintain normal con-
centration in blood but at a slow rate since there is
no direct mobilizing mechanism for phosphorus as
there is for calcium. Since the two elements are
combined in bone, the mobilization of calcium, as a
result of parathyroid gland action, is accompanied by
the incidental mobilization of phosphorus. Animals
with chronic phosphorus deficiency sometimes become
stiff in the joints and in severe cases, are charac-
terized by fragile bones.
About 86% of the phosphorus in cattle is found in
the skeleton and teeth and the remainder in soft
tissues. Bone ash contains about 17% phosphorus.
Blood serum varies in concentration from 3.0 to 8.0
mg of phosphorus/deciliter (dL) (Table 1).
Phosphorus is absorbed in the small intestine as
phosphate. Since phosphorus combines spontaneously
with other elements, it is present in the body in the
phosphate form (PO3). In the bones it occurs as
calcium hydroxyapatite. All cells possess enzymes
that can attach phosphates in ester or acid anhydride
linkages to other molecules. Enzymes exist both


inside and outside of the cells which remove phos-
phates from phosphate-containing molecules.

Table 1. Normal levels of selected minerals in blood serum.
Component Normal Values
(mg/dL)'

Calcium 9-10.6
Magnesium 1-3
Phosphorus 3-8
Potassium 14-20
Sodium 310-340
'dL = 0.1 liter or 100 milliliters.

Phosphorus Requirements
Phosphorus requirements are highest during
lactation, early growth, and for reproduction. High-
producing cows need much more phosphorus than
cows producing at average or low levels. Dry cows or
cows that are not producing milk need less phosphor-
us than lactating cows due to the high content of
phosphorus in milk.
Milk contains about 0.12% calcium and 0.095%
phosphorus. A cow producing 100 pounds of milk
daily would require 100 g (0.220 lb) of phosphorus
and secrete 43 g (0.095 lb) of phosphorus in milk.
Because of the high level of phosphorus in milk, a
continuous supply is needed in the ration in order to
allow high levels of milk production. The amounts of
phosphorus required by dairy cattle, as set forth by
the subcommittee on Dairy Cattle Nutrition of the
National Research Council, are in Tables 2 and 8.
Rations for lactating dairy cattle are formulated to
contain a given quantity or percent of phosphorus in
order to meet the requirements for that specific
nutrient. A lactating dairy cow producing 70 lbs of
milk and consuming 47 lbs of dry matter (DM) daily


B. Harris, Jr. is a Professor and Extension Dairy Specialist with the Dairy Science Department at the Institute of Food and
Agricultural Sciences, University of Florida, Gainesville, FL. D. Morse is an Extension Dairy Specialist at North Dakota State
University in Fargo, N.D. H.H. Head is a Professor in the Dairy Science Department at the University of Florida, Gainesville, FL.
H.H. Van Horn is a Professor and Extension Waste Management Specialist at the University of Florida, Gainesville, FL.









Table 2. Daily nutrient requirements for growing, dry, and lactating dairy cattle (3.5% fat, 1400 Ib body wt.).

Live Milk Minerals
wt Gain Yield Ca Phos DMI TDN CP
(Ib) (Ib) (Ib) (gms) (gms) ......... ---------lbs--------

90 0.6 -6.8 4.1 1 1.32 0.24
150 1.7 15.4 7.7 4 3.92 0.77
300 1.7 -- 19.5 11.4 8 5.56 1.29
700 1.7 24.9 18.6 16 10.27 1.94
900 1.7 28.6 20.9 21 12.75 2.52
1400 (Dry) 25.9 18.2 -- 12.75 2.52
1400 (Late Dry) 41.8 25.4 -- 12.90 2.20
1400 35 73.5 46.7 35 21.00 4.20
1400 70 121.1 75.3 47 30.83 6.90
1400 100 162.0 100.0 58 39.90 9.27

1453.6 grams = 1 pound; DMI = dry matter intake; TDN = total digestible nutrients; CP = crude protein.

and receiving a ration containing 0.4% phosphorus consuming 8.06 pounds of dry matter daily would
would receive the needed 82 grams of phosphorus as need a total ration containing 0.33% phosphorus in
shown in Table 2 (47 x 0.004 = 0.188 lb x 453.6) = the DM to provide the needed 12 grams. The
85 grams. phosphorus requirements for growing heifers gradual-
Dry cows are those not producing milk after ly increases as the animals become more mature,
having completed a lactation. They are usually with little to no increase beyond 900 pounds of body
separated into two groups and noted as early and late weight.
dry cows. Late dry or springer cows are handled
more carefully since they are in the last month of Phosphorus Sources and Availability
gestation when the fetus is growing at an accelerated
rate. As shown in Table 3, they need more phos- Ruminant animals obtain phosphorus from most
phorus than the early dry cows. feedstuffs fed to them. High quality forages tend to
Growing heifers weighing about 300 pounds need be low in phosphorus but concentrates are fairly good
12 grams of phosphorus daily (Table 2). Since sources. Much of the phosphorus found in some
heifers are fed to meet their energy and protein cereal grains is bound to a chemical compound
requirements, the total ration dry matter (DM) would named phytate (Table 3). This source of phosphorus
need to contain an adequate amount of phosphorus is poorly utilized by simple stomached animals
in addition to other required nutrients. A heifer (poultry, swine, etc.) but is readily available to


Table 3. Concentration of total phosphorus and phosphorus bound to phytate in selected feedstuffs.
Phytate Phytate
Number Total Phos. Phos. Phos.
Feedstuff Samples -ppm1 -... %

Cottonseed meal 2 12220 8480 69.4
Distillers, dried 2 8990 2880 32.0
Corn meal 3 2980 1900 63.8
Hominy feed 3 6380 4680 73.4
Peanut meal 2 6650 3800 57.1
Rice bran 2 15780 12560 79.6
Soybean meal 2 7320 5020 68.6
Wheat midds 3 13400 10480 78.2
'ppm = parts per million








Esophagus


Rumen
(first stomach)
the paunch or store house


Omasum
(third stomach)



zjg
.^.^^ ^W -' ~ ; "' *."
**' :f.' .


Reticulum
(second stomach)


(ifot Abomasum .
,,. (fourth or true stomach)


Figure 1. Digestive system of the ruminant animal.

ruminants. Ruminants have a true stomach or
abomasum as you would find in monogastric animals.
In addition, ruminant animals have three other
compartments (Figure 1). The rumen and reticulum
make up a large fermentation vat where large num-
bers of bacteria and protozoa produce many enzymes
that aid in digesting the consumed feed. The third
compartment, the omasum, provides an absorption
area even greater than the rumen.
Because of the unique digestive tract, ruminants
utilize feedstuffs after a predigestion in the rumen-
reticulum.
The forward location of the rumen gives the
microbes priority to the soluble carbohydrates and
proteins, as well as vitamins and minerals that are
consumed. The more complex carbohydrates such as
cellulose and hemicellulose that are in roughages are
degraded at a much slower rate than the starches in
corn. The microbes attach and degrade the complex
feedstuffs into more simple compounds such as fatty
acids and amino acids. Also, minerals and vitamins
are released in the process and become available to
the animal. Such is the case for phosphorus bound
to phytate. Rumen microbes produce an enzyme
called "phytase" that degrades the complex compound.
As a result, phosphorus is released and available for


absoption and utilization (Table 3).Recent studies by
Clark et al. (1986) and Morse (1989) confirm research
by Reid et al. (1947) with sheep which showed that
a large percentage of the phosphorus bound to
phytate was utilized. Studies by Morse, (1989)
indicated that 99% to 100% of the phosphorus bound
to phytate was hydrolyzed within a period of about
24 hours in rumen fluid (in vitro studies) and would
be available for utilization (Table 4). While phytate
phosphorus is well utilized, most dairy cattle rations
still require further supplementation with inorganic
sources of phosphorus such as defluorinated or
dicalcium phosphate.
A number of feedstuffs are relatively high in
phosphorus and, when used in combination or at
levels of 10%-20%, tend to meet or exceed the re-
quirements for phosphorus in the ration without
further supplementation. Some of the more common
ingredients high in phosphorus are in Table 5.


Phosphorus Absorption
Phosphorus absorption occurs in the small intes-
tine. The amount of phosphorus absorbed by the
animal depends on the source of the phosphorus, the


-&..


Pylorus









Table 4. Percent disappearance of P bound to phytate with
time in rumen fluid.
Hours of Incubation in Rumen Fluid1
Ingredient 2 6 12 24
Wheat mldds 84.5 94.9 98.1 99.8
Rice bran 85.3 82.6 98.1 99.8
Hominy feed 52.5 90.0 99.4 99.8
Soybean meal 31.3 50.2 99.9 100
Dried distillers grain 71.3 95.4 98.7 99.3
Cottonseed meal 48.7 57.0 71.5 99.9

'Morse, 1989.

amount of intake, the calcium-phosphorus ratio,
intestinal pH, disease and parasites, environment,
the age of the animal, and dietary levels of calcium,
iron, aluminum, manganese, potassium, magnesium
and fat. Many of these factors become important
when nutrients in diets are low or deficient. The
regulation of phosphate absorption is mediated by
vitamin D, (1,25-dihydroxyvitamin D3). When the
serum phosphate level is abnormally low, the forma-
tion of 1,25-dihydroxyvitamin D3 in the renal tubule
of the kidney is stimulated, causing enhanced phos-
phate absorption from the intestine. Ruminants
recycle large amounts of phosphorus as inorganic
phosphate in saliva, in which secretion appears to be
regulated by the parathyroid hormone. Also, the
parathyroid hormone along with vitamin D is in-
volved in the mobilization of calcium and phosphate
from bone.


Phosphorus and Milk Fever
An important concern dairymen have when reduc-
ing the amount of phosphorus in rations is the
impact on milk fever incidence. Milk fever is a
metabolic disorder that is associated with the level of
phosphorus and calcium intake during the late dry
period or very early lactation. It is caused by a
sudden drop in the calcium content in the blood.
Phosphorus appears to affect the cow's ability to
mobilize calcium from bone and to absorb calcium
efficiently from the intestine. Noticeable early
symptoms are unsteadiness in walking, eyes dull and
staring, pupils dilated, sleepy attitude and cold ears.
As the case develops, the cow will be found lying
down with her head displaced to one side or tucked
into her flank. Complete paralysis, coma, and death
occur unless an intravenous injection of a calcium
solution is given.
During the dry period, it is desirable to not
overfeed calcium and to maintain diet calcium and
phosphorus near or slightly less than a 1.5 to 1.0
ratio. During lactation, problems are not usually
encountered with a wider ratio as long as the level of
phosphorus meets the animal's requirements.
Nutrient changes in a ration should be made
gradually. This also is the case for phosphorus,
especially when moving from a fairly high level to a
lower level in the diet. The National Research
Council recommends that the total ration dry matter
for the late dry pregnant cow contain a minimum of


Table 5. Feedstuffs commonly used in Dairy Cattle Rations (as fed).

Feedstuff CP1 TDN' Calcium Phosphorus
(%) (%) (%) (%)
Canola meal 37 64 .68 1.10
Corn gluten feed 21 74 .30 .76
Corn gluten meal 60 82 .02 .62
Cottonseed, whole 21 90 .14 .68
Cottonseed meal 41 70 .20 .90
Malt sprouts 20 65 .20 .70
Peanut meal 50 74 .20 .60
Rice bran 12 60 .60 1.40
Rice mill feed 6 32 .08 1.30
Soybean meal 44 78 .20 .60
Wheat midds 16 76 .10 .90
'CP = crude protein; TDN = total digestible nutrients









0.39% calcium, 0.24% phosphorus and 0.16% mag-
nesium. The exact percent needed, however, would
depend on the type and amount of ration being fed.
Since milk fever usually occurs at or near the time
of calving and is more related to feeding during the
late dry period, it is important that a good feeding
program be developed for the dry cows. Just as
sodium and potassium are associated with udder
edema, calcium, phosphorus and sometimes mag-
nesium are associated with the incidence of milk
fever in a herd.
In 1964, Harris reported that borderline levels of
phosphorus and higher than needed levels of calcium
were associated with increased incidence of milk fever
in many herds. The high level of calcium (Ca) fed
was attributed to the high level of citrus pulp (1-3%
Ca) included in the diets (normally 30-45% of diet).
To combat the high incidence of milk fever, dietary
phosphorus was increased. This simultaneously
reduced the Ca:P ratio and reduced the incidence of
milk fever. The level of phosphorus in dairy cattle
rations tended to increase over the next few years
since it was believed that phytate-bound phosphorus
was unavailable to animals. As a result, discount
values were established for certain feedstuffs. This
resulted in a higher level of phosphorus in some
rations. Research by Morse (1989) shows that these
discount values are unnecessary.


Research to Reduce Excretion
A problem of great concern in South Florida is the
concentration of phosphorus in Lake Okeechobee.
This large lake (1900 square kilometers) ranging from
5 to 6 meters in depth, supplies drinking water to
communities around the lake, serves as reserve water
for Florida's southeast coast, and provides water to
the Florida everglades. The lake also serves as a
recreational facility and provides some of the best
sports fishing in the United States. Nutrient rich
runoff from farm lands enters the lake and significant
phosphorus contamination originates from the dairy
farms (>35,000 dairy cows) in the Taylor Creek-
Nubbin Slough watershed. As concentration of
phosphorus in the lake water increases, algae growth
increases which may deplete the water of oxygen and
disturb the ecosystem.
Graetz (1989) reported that waters originating
from the northern end of the lake contain high
concentration of phosphorus in the water. Since
phosphorus has been identified as a troublesome
nutrient to the ecosystems of Lake Okeechobee,
research was needed to better define phosphorus
intake versus phosphorus excretion.


Okeechobee Field Trial
During 1986-87, a study was conducted in the
Okeechobee area to determine the effects of different
levels of phosphorus intake on the excretion of
phosphorus in feces. Five dairies, each milking 700
to 1550 cows were included in the study. Production
and reproduction data were available for many of the
cows sampled. One dairy had only first lactation
cows, whereas other dairies had both first and
greater lactation cows. Feed for these dairies was
supplied by United Feed Cooperative (UFC) or Dairy
Feeds, Inc. (DFI).
Concentrate portions of diets were formulated by
feed mills for .42% phosphorus on two dairies, and
.52% P on three dairies. Free choice mineral mix
with minimum of 8.0% phosphorus was available for
cows on one dairy where cows were fed .52% phos-
phorus. Feedstuffs used in the rations formulated
included cottonseed hulls, malt sprout pellets,
hominy, whole cottonseed, wheat middlings, soybean
hulls, corn meal, cottonseed meal and rice bran.
Feed, fecal and bulk milk samples were collected
monthly at each dairy. Fecal samples were retrieved
per rectum from 20 randomly selected cows on each
dairy. Also, samples of whole blood were taken from
10 to 15 randomly selected cows at each dairy.
Concentration of phosphorus in the blood serum was
an indication of phosphorus status of cows. The
results are in Table 6.
Phosphorus in the feces decreased when the
concentration of phosphorus in the ration was de-
creased. Cows allowed access to free choice mineral
had a greater concentration of phosphorus in the

Table 6. Concentration of phosphorus found in the con-
centrate, feces and blood serum of dairy cows.

Phosphorus Concentration
Total diet feces serum
(% of DM) ppm (mg/dL)

DLD 1" 0.57 7317 5.98
DLD 2 (Low) 0.47 6344 6.33
MF 1 (Low) 0.51 6942 5.89
MF 3(free choice) 0.71 9533 6.28
MF 4 0.71 8931 6.01
aDLD = Dry Lake Dairies Barns 1 and 2.
MF McArthur Farms Bars 1, 3, and 4.

feces (MF3 vs MF4). The major dietary difference
between cows at MF3 and MF4 was availability of
free choice mineral at MF3.









0.39% calcium, 0.24% phosphorus and 0.16% mag-
nesium. The exact percent needed, however, would
depend on the type and amount of ration being fed.
Since milk fever usually occurs at or near the time
of calving and is more related to feeding during the
late dry period, it is important that a good feeding
program be developed for the dry cows. Just as
sodium and potassium are associated with udder
edema, calcium, phosphorus and sometimes mag-
nesium are associated with the incidence of milk
fever in a herd.
In 1964, Harris reported that borderline levels of
phosphorus and higher than needed levels of calcium
were associated with increased incidence of milk fever
in many herds. The high level of calcium (Ca) fed
was attributed to the high level of citrus pulp (1-3%
Ca) included in the diets (normally 30-45% of diet).
To combat the high incidence of milk fever, dietary
phosphorus was increased. This simultaneously
reduced the Ca:P ratio and reduced the incidence of
milk fever. The level of phosphorus in dairy cattle
rations tended to increase over the next few years
since it was believed that phytate-bound phosphorus
was unavailable to animals. As a result, discount
values were established for certain feedstuffs. This
resulted in a higher level of phosphorus in some
rations. Research by Morse (1989) shows that these
discount values are unnecessary.


Research to Reduce Excretion
A problem of great concern in South Florida is the
concentration of phosphorus in Lake Okeechobee.
This large lake (1900 square kilometers) ranging from
5 to 6 meters in depth, supplies drinking water to
communities around the lake, serves as reserve water
for Florida's southeast coast, and provides water to
the Florida everglades. The lake also serves as a
recreational facility and provides some of the best
sports fishing in the United States. Nutrient rich
runoff from farm lands enters the lake and significant
phosphorus contamination originates from the dairy
farms (>35,000 dairy cows) in the Taylor Creek-
Nubbin Slough watershed. As concentration of
phosphorus in the lake water increases, algae growth
increases which may deplete the water of oxygen and
disturb the ecosystem.
Graetz (1989) reported that waters originating
from the northern end of the lake contain high
concentration of phosphorus in the water. Since
phosphorus has been identified as a troublesome
nutrient to the ecosystems of Lake Okeechobee,
research was needed to better define phosphorus
intake versus phosphorus excretion.


Okeechobee Field Trial
During 1986-87, a study was conducted in the
Okeechobee area to determine the effects of different
levels of phosphorus intake on the excretion of
phosphorus in feces. Five dairies, each milking 700
to 1550 cows were included in the study. Production
and reproduction data were available for many of the
cows sampled. One dairy had only first lactation
cows, whereas other dairies had both first and
greater lactation cows. Feed for these dairies was
supplied by United Feed Cooperative (UFC) or Dairy
Feeds, Inc. (DFI).
Concentrate portions of diets were formulated by
feed mills for .42% phosphorus on two dairies, and
.52% P on three dairies. Free choice mineral mix
with minimum of 8.0% phosphorus was available for
cows on one dairy where cows were fed .52% phos-
phorus. Feedstuffs used in the rations formulated
included cottonseed hulls, malt sprout pellets,
hominy, whole cottonseed, wheat middlings, soybean
hulls, corn meal, cottonseed meal and rice bran.
Feed, fecal and bulk milk samples were collected
monthly at each dairy. Fecal samples were retrieved
per rectum from 20 randomly selected cows on each
dairy. Also, samples of whole blood were taken from
10 to 15 randomly selected cows at each dairy.
Concentration of phosphorus in the blood serum was
an indication of phosphorus status of cows. The
results are in Table 6.
Phosphorus in the feces decreased when the
concentration of phosphorus in the ration was de-
creased. Cows allowed access to free choice mineral
had a greater concentration of phosphorus in the

Table 6. Concentration of phosphorus found in the con-
centrate, feces and blood serum of dairy cows.

Phosphorus Concentration
Total diet feces serum
(% of DM) ppm (mg/dL)

DLD 1" 0.57 7317 5.98
DLD 2 (Low) 0.47 6344 6.33
MF 1 (Low) 0.51 6942 5.89
MF 3(free choice) 0.71 9533 6.28
MF 4 0.71 8931 6.01
aDLD = Dry Lake Dairies Barns 1 and 2.
MF McArthur Farms Bars 1, 3, and 4.

feces (MF3 vs MF4). The major dietary difference
between cows at MF3 and MF4 was availability of
free choice mineral at MF3.









Table 7. Least squares means for three levels of phosphorus on excretion of phosphorus in feces, milk and urine.
Low Medium High
Measurement (.30%; 60 g/d) (.41%; 82 g/d) (.56%; 112 g/d)

Feces (g/d) 40.30 45.10 62.94
Milk (g/d) 18.40 20.40 22.00
Urine (g/d) .66 1.26 3.36


Intake and Excretion
The Okeechobee field trial indicated some relation-
ship exists between phosphorus intake and phosphor-
us excretion. Lomba et al. (1969) summarized 14
experiments in mature, lactating, non-pregnant dairy
cows producing 24 to 44 pounds of milk daily and
found no relationship between dietary phosphorus
intake and excretion. Two additional experiments
were conducted at the University of Florida to
evaluate the effects of phosphorus intake on amount
and route of phosphorus excretion and on level of
phosphorus in diet on voluntary feed intake and milk
production.
Twelve Holstein cows were used in a 13-week
continuous trial in the first experiment. Cows were
assigned randomly to one of three dietary concentra-
tions of phosphorus: .30%, .41% or .56% of diet dry
matter (DM). These diets are identified as low (L),
medium (M), and high (H) in concentration of
phosphorus and represent 79% (deficient), 108%
(adequate), and 147% (excess) of recommended
nutrient requirements for a 1300-lb dairy cow pro-
ducing between 46 lb and 70 lb of 4% fat milk daily
(NRC, 1988).
The study showed that the concentration of phos-
phorus in feces was altered by the concentration of
phosphorus in the diet but had little or no effect on
amount of phosphorus excreted in milk or urine
(Table 7). Increasing the intake of phosphorus from
82 g/d to 112 g/d resulted in a 48.6% increase in the
excretion of phosphorus in feces. Reducing the


intake of phosphorus from 82 g/d to 60 g/d resulted
in a 22.7% decrease in the excretion of phosphorus in
feces.
Since voluntary feed intake was restricted to 44 lbs
of DM/d for these cows, a second trial was conducted
using 24 Holstein cows to study the effect of different
levels of dietary phosphorus and Ca on voluntary feed
intake and milk production and composition. Levels
of phosphorus used were .33%, .43%, and .54% of
ration DM. Again, these levels represented less,
adequate, or high level of phosphorus in diet of high-
producing cows relative to NRC requirement (0.41%
of diet DM as phosphorus; NRC, 1988). Concentra-
tions of Ca were .60% and .97% of diet DM repre-
senting 100% and 162% of currently recommended
concentrations of Ca (NRC, 1988).
Concentrations of dietary phosphorus (.33%, .43%,
and .54% of DM) did not affect voluntary intake of
feed or production of milk. Although milk production
tended to be higher on low phosphorus, the results
showed no difference in DM intake for ratios of Ca:P
between 1.1:1 and 2.9:1. There was a trend for DM
intake to increase with decreased concentration of
phosphorus. Production of 3.5% FCM was 4.8%
greater in cows fed a .60% calcium diet when com-
pared to cows fed a .97% Ca diet.


Formulating Rations
Consideration should be given to the total ration
when formulating premises, mineral mixtures or the
concentrate portion of the ration. A balanced ration


Table 8. Calcium and phosphorus requirements of small cows producing 4.5% milk fat and larger cows producing 3.5%
milk fat.

Wt. Milk Ca. Phos. Wt. Milk Ca. Phos.
------------............. lb -----------............ b -------------
1000 35 .164 .103 1000 75 .304 .187
1400 35 .162 .103 1400 75 .282 .175
1000 50 .216 .134 1400 80 .297 .184
1400 50 .207 .130 1400 85 .312 .193
1000 65 .269 .166 1400 90 .327 .202
1400 65 .252 .157 1400 100 .357 .220









Table 7. Least squares means for three levels of phosphorus on excretion of phosphorus in feces, milk and urine.
Low Medium High
Measurement (.30%; 60 g/d) (.41%; 82 g/d) (.56%; 112 g/d)

Feces (g/d) 40.30 45.10 62.94
Milk (g/d) 18.40 20.40 22.00
Urine (g/d) .66 1.26 3.36


Intake and Excretion
The Okeechobee field trial indicated some relation-
ship exists between phosphorus intake and phosphor-
us excretion. Lomba et al. (1969) summarized 14
experiments in mature, lactating, non-pregnant dairy
cows producing 24 to 44 pounds of milk daily and
found no relationship between dietary phosphorus
intake and excretion. Two additional experiments
were conducted at the University of Florida to
evaluate the effects of phosphorus intake on amount
and route of phosphorus excretion and on level of
phosphorus in diet on voluntary feed intake and milk
production.
Twelve Holstein cows were used in a 13-week
continuous trial in the first experiment. Cows were
assigned randomly to one of three dietary concentra-
tions of phosphorus: .30%, .41% or .56% of diet dry
matter (DM). These diets are identified as low (L),
medium (M), and high (H) in concentration of
phosphorus and represent 79% (deficient), 108%
(adequate), and 147% (excess) of recommended
nutrient requirements for a 1300-lb dairy cow pro-
ducing between 46 lb and 70 lb of 4% fat milk daily
(NRC, 1988).
The study showed that the concentration of phos-
phorus in feces was altered by the concentration of
phosphorus in the diet but had little or no effect on
amount of phosphorus excreted in milk or urine
(Table 7). Increasing the intake of phosphorus from
82 g/d to 112 g/d resulted in a 48.6% increase in the
excretion of phosphorus in feces. Reducing the


intake of phosphorus from 82 g/d to 60 g/d resulted
in a 22.7% decrease in the excretion of phosphorus in
feces.
Since voluntary feed intake was restricted to 44 lbs
of DM/d for these cows, a second trial was conducted
using 24 Holstein cows to study the effect of different
levels of dietary phosphorus and Ca on voluntary feed
intake and milk production and composition. Levels
of phosphorus used were .33%, .43%, and .54% of
ration DM. Again, these levels represented less,
adequate, or high level of phosphorus in diet of high-
producing cows relative to NRC requirement (0.41%
of diet DM as phosphorus; NRC, 1988). Concentra-
tions of Ca were .60% and .97% of diet DM repre-
senting 100% and 162% of currently recommended
concentrations of Ca (NRC, 1988).
Concentrations of dietary phosphorus (.33%, .43%,
and .54% of DM) did not affect voluntary intake of
feed or production of milk. Although milk production
tended to be higher on low phosphorus, the results
showed no difference in DM intake for ratios of Ca:P
between 1.1:1 and 2.9:1. There was a trend for DM
intake to increase with decreased concentration of
phosphorus. Production of 3.5% FCM was 4.8%
greater in cows fed a .60% calcium diet when com-
pared to cows fed a .97% Ca diet.


Formulating Rations
Consideration should be given to the total ration
when formulating premises, mineral mixtures or the
concentrate portion of the ration. A balanced ration


Table 8. Calcium and phosphorus requirements of small cows producing 4.5% milk fat and larger cows producing 3.5%
milk fat.

Wt. Milk Ca. Phos. Wt. Milk Ca. Phos.
------------............. lb -----------............ b -------------
1000 35 .164 .103 1000 75 .304 .187
1400 35 .162 .103 1400 75 .282 .175
1000 50 .216 .134 1400 80 .297 .184
1400 50 .207 .130 1400 85 .312 .193
1000 65 .269 .166 1400 90 .327 .202
1400 65 .252 .157 1400 100 .357 .220










is one that provides the nutrients in such proportions
and amounts that will properly nourish a given
animal for 24 hours (Morrison, 1956). In addition,
consideration must be given to the amount of dry
matter the animal is able to or will consume during
the 24-hour period. In formulating rations, a number
of components are usually considered such as protein,
energy, fiber, minerals and vitamins. In this discus-
sion, we are primarily interested in the level of
phosphorus in rations and how it relates to calcium,
magnesium, protein and energy.
Some feedstuffs are better sources of minerals that
others (Table 3). While textbook values are common-
ly used for many feedstuffs, an analysis of the forage
is preferred since they vary considerably in composi-
tion. This is especially true for legume forages which
are relatively high in minerals.
In addition to formulating balanced rations for
dairy cattle, attention must be given to meeting the
nutrient requirements of the cow at the lowest
possible cost. Computer programs are available to
assist in the formulation of optimum diets at mini-
mum costs. Table 8 contains the requirements for
calcium and phosphorus for lactating cows (NRC,
1988).


A few examples of total mixed rations are present-
ed to show the level of calcium and phosphorus
needed by dairy cattle as outlined in Table 8.
Ration 1 is a high energy ration that contains
0.79% calcium and 0.48% phosphorus on a dry basis.
Since ration 2 contains a lower energy roughage
source, less calcium and phosphorus is needed as a
percent of the dry matter since dry matter intakes
are greater when cows receive cottonseed hull rations.
Ration 3 contains rice bran which is an excellent
source of phosphorus. Note that the mineral supple-
ment contains no phosphorus. Ration 4 contains
some green chop and bermuda hay in addition to a
purchased grain mix that contains cottonseed hulls.
Many Florida dairymen purchase a premix or
concentrate to blend with the forages available on the
farm. Since forages tend to be low in phosphorus, a
greater percent of phosphorus is needed in the
concentrate. Such is the case with rations 1, 2, 3
and 4 where both the forage type and amount varies
in the ration and the percent in the total ration dry
matter varies from 0.43 to 0.49%.


RATION NO. 1


Dry Crude Crude
Ibs Matter Protein TDN CA PHOS Fiber
..................... -----lbs-...---.---.....----.........
Corn Silage 45.00 13.50 1.13 9.00 0.04 0.02 4.05
Alfalfa Hay 6.00 5.34 1.08 3.00 0.05 0.01 1.68
Corn Meal 8.00 7.20 0.69 6.40 .00 0.02 0.24
Whole Cottonseed 5.00 4.50 1.05 4.50 0.01 0.03 0.85
Wheat Midds 3.00 2.67 0.48 2.28 .00 0.03 0.18
Soybean Hulls 3.00 2.67 0.36 1.95 0.01 .00 0.36
Distillers grains 3.00 2.70 0.78 2.40 .00 0.01 0.36
Soybean Meal (48%) 4.20 3.78 2.02 3.19 0.01 0.03 0.08
Mineral 1.40 1.32 0.00 0.00 0.02 0.05 0.00
Total Intake 78.60 43.68 7.58 32.72 0.34 0.21 7.80
Requirements (70# Milk) 7.50 32.30 0.32 0.20 -
Ration Percent Dry Matter 17.35 74.92 0.79 0.48 17.87











RATION NO. 2


Dry Crude Crude
lbs Matter Protein TDN CA PHOS Fiber


Cottonseed Hulls
Alfalfa Hay
Corn Meal
Whole Cottonseed
Wheat Midds
Soybean Hulls
Distillers grains
Soybean Meal (48%)
Mineral
Total Intake

Requirements (70# Milk)

Ration Percent Dry Matter


12.00
8.00
11.00
5.00
4.00
3.00
3.00
4.00
1.50
51.50


.................... Ibs ------------------
10.00 0.48 4.80 0.02 0.01 5.16
7.12 1.44 4.00 0.06 0.02 2.24
9.90 0.95 8.80 .00 0.03 0.33
4.50 1.05 4.50 0.01 0.03 0.85
3.56 0.64 3.04 .00 0.04 0.24
2.67 0.36 1.95 0.01 .00 0.36
2.70 0.78 2.40 .00 0.01 0.36
3.60 2.92 3.04 0.01 0.02 0.08
1.41 0.00 0.00 0.24 0.04 0.00
46.26 7.62 32.53 0.35 0.21 9.62


7.50 32.30 0.32 0.20

16.46 70.32 0.76 0.45


20.80


RATION NO. 3


Dry Crude Crude
Ibs Matter Protein TDN CA PHOS Fiber


Cottonseed Hulls
Bermuda Hay
Hominy Feed
Whole Cottonseed
Rice Bran
Distillers Grains
Peanut Meal
Mineral
Total Intake


Requirements (70# Milk)

Ration Percent Dry Matter


-l.....- ..--- .. .... -Ibs ------------------
13.00 11.70 0.52 5.20 0.02 0.01 5.59
6.00 5.34 1.02 2.28 0.02 0.01 1.92
15.00 13.50 1.50 12.30 0.01 0.08 0.45
5.50 4.95 1.16 4.95 0.01 0.04 0.94
4.00 3.56 0.48 2.40 .00 0.06 0.40
3.00 2.70 0.78 2.40 .00 0.01 0.36
4.20 3.78 2.10 3.19 0.01 0.03 0.17
1.60 1.50 0.00 0.00 0.28 0.00 0.00
52.30 47.03 7.56 32.72 0.34 0.23 9.82


7.50 32.30 0.32 0.20


16.06 69.57 0.72 0.49 20.88





'0 -", Trk
. t .I .


RATION NO. 4
Dry Crude Crude
Ibs Matter Protein TDN CA PHOS Fiber
--------------------Ibs -----------------
Bermuda Hay 7.00 6.16 0.49 2.80 0.02 0.01 2.24
CSH Grain Mix 41.00 36.90 6.56 26.65 0.31 0.19 6.15
Green Chop 30.00 6.00 0.45 3.60 0.02 0.01 1.80
Total Intake 78.00 49.06 7.50 33.05 0.35 0.21 10.19

Requirements (70# Milk) 7.50 32.30 0.32 0.20

Ration Percent Dry Matter 15.29 67.37 0.71 0.43 20.77


Summary
Phosphorus is an important mineral element which
is key to energy metabolism and is an essential
component of buffer systems in blood and other body
fluids.
Phosphorus requirements of dairy cows vary
according to level of milk production, body size and
stage of gestation. As an example, a 1400-lb dairy
cow producing 85 lbs of 3.5% milk needs about 88 g
(.20 Ibs) of phosphorus daily as compared to 59 g
(.13 Ibs) for a similar cow producing 50 lbs of milk
(NRC, 1988).
Phosphorus bound to phytate accounts for a large
amount of the phosphorus present in feedstuffs
commonly fed to dairy cattle. The results' of our
studies revealed that 99% to 100% of the phosphorus
bound to phytate would be hydrolyzed in the diges-
tive tract and be available for utilization. There was
no evidence to indicate or suggest any discounting
value of phosphorus bound to phytate when formulat-
ing diets for lactating dairy cows.
Phosphorus is excreted primarily through feces and
milk. The level of phosphorus in milk appears to
remain constant with different levels of phosphorus
in the ration. Once cows attain a balance of phos-
phorus for body functions and needs, the amount of
phosphorus excreted in the feces will increase.
Research indicates that the NRC (1988) recom-
mended level of phosphorus (0.4 to 0.43% of ration
dry matter) for lactating dairy cows is enough for
optimum performance. Feeding more increases the
amount excreted in the feces. Restricting dietary
intake of phosphorus to NRC allowances will help to
reduce the amount of phosphorus excreted in the
feces while providing adequate phosphorus for other
body functions.


Selected References
1. Clark, W. D., Jr., J. E. Wohlt, R. L. Gilbreath, and P.
K Zajac. 1986. Phytate phosphorus intake and
disappearance in the gastrointestinal tract of high
producing dairy cows. J. Dairy Sci. 69:3151.

2. Graetz, D. A. 1989. Phosphorus levels in soils of
selected Lake Okeechobee watershed dairies. Proc.
Florida Dairy Production Conf., Gainesville, Fl. pp. 113-
118.

3. Harris, B. Jr. 1964. Minerals in dairy rations. Florida
Dairy Extension Newsletter.

4. Lomba, F., R. Paguay, V. Bienfet, and A. Lousse. 1969.
Statistical research on the fats of dietary mineral
elements in dry and lactating cows. I. Phosphorus.
J. Agric. Sci 73:215

5. Morrison, F. B. 1956. Feeds and feeding. 22nd Ed.
The Morrison Publishing Co., Clinton, Iowa.

6. Morse, D. 1989. Studies of modification of phosphorus
concentration in diets, hydrolysis of phytate bound
phosphorus, and excretion of phosphorus by dairy cows.
PhD Dissertation

7. National Research Council. 1988. Nutrient require-
ments of dairy cattle, 6th rev. ed. Washington, D.C.:
National Academy Press.

8. Reid, R. L., M. C. Franklin, and E. G. Hallsworth.
1947. The utilization of phytate phosphorus by sheep.
Aust. Vet. J. 23:136.





'0 -", Trk
. t .I .


RATION NO. 4
Dry Crude Crude
Ibs Matter Protein TDN CA PHOS Fiber
--------------------Ibs -----------------
Bermuda Hay 7.00 6.16 0.49 2.80 0.02 0.01 2.24
CSH Grain Mix 41.00 36.90 6.56 26.65 0.31 0.19 6.15
Green Chop 30.00 6.00 0.45 3.60 0.02 0.01 1.80
Total Intake 78.00 49.06 7.50 33.05 0.35 0.21 10.19

Requirements (70# Milk) 7.50 32.30 0.32 0.20

Ration Percent Dry Matter 15.29 67.37 0.71 0.43 20.77


Summary
Phosphorus is an important mineral element which
is key to energy metabolism and is an essential
component of buffer systems in blood and other body
fluids.
Phosphorus requirements of dairy cows vary
according to level of milk production, body size and
stage of gestation. As an example, a 1400-lb dairy
cow producing 85 lbs of 3.5% milk needs about 88 g
(.20 Ibs) of phosphorus daily as compared to 59 g
(.13 Ibs) for a similar cow producing 50 lbs of milk
(NRC, 1988).
Phosphorus bound to phytate accounts for a large
amount of the phosphorus present in feedstuffs
commonly fed to dairy cattle. The results' of our
studies revealed that 99% to 100% of the phosphorus
bound to phytate would be hydrolyzed in the diges-
tive tract and be available for utilization. There was
no evidence to indicate or suggest any discounting
value of phosphorus bound to phytate when formulat-
ing diets for lactating dairy cows.
Phosphorus is excreted primarily through feces and
milk. The level of phosphorus in milk appears to
remain constant with different levels of phosphorus
in the ration. Once cows attain a balance of phos-
phorus for body functions and needs, the amount of
phosphorus excreted in the feces will increase.
Research indicates that the NRC (1988) recom-
mended level of phosphorus (0.4 to 0.43% of ration
dry matter) for lactating dairy cows is enough for
optimum performance. Feeding more increases the
amount excreted in the feces. Restricting dietary
intake of phosphorus to NRC allowances will help to
reduce the amount of phosphorus excreted in the
feces while providing adequate phosphorus for other
body functions.


Selected References
1. Clark, W. D., Jr., J. E. Wohlt, R. L. Gilbreath, and P.
K Zajac. 1986. Phytate phosphorus intake and
disappearance in the gastrointestinal tract of high
producing dairy cows. J. Dairy Sci. 69:3151.

2. Graetz, D. A. 1989. Phosphorus levels in soils of
selected Lake Okeechobee watershed dairies. Proc.
Florida Dairy Production Conf., Gainesville, Fl. pp. 113-
118.

3. Harris, B. Jr. 1964. Minerals in dairy rations. Florida
Dairy Extension Newsletter.

4. Lomba, F., R. Paguay, V. Bienfet, and A. Lousse. 1969.
Statistical research on the fats of dietary mineral
elements in dry and lactating cows. I. Phosphorus.
J. Agric. Sci 73:215

5. Morrison, F. B. 1956. Feeds and feeding. 22nd Ed.
The Morrison Publishing Co., Clinton, Iowa.

6. Morse, D. 1989. Studies of modification of phosphorus
concentration in diets, hydrolysis of phytate bound
phosphorus, and excretion of phosphorus by dairy cows.
PhD Dissertation

7. National Research Council. 1988. Nutrient require-
ments of dairy cattle, 6th rev. ed. Washington, D.C.:
National Academy Press.

8. Reid, R. L., M. C. Franklin, and E. G. Hallsworth.
1947. The utilization of phytate phosphorus by sheep.
Aust. Vet. J. 23:136.





UNIVERSITY OF FLORIDA

3 1262 05177 3637


This publication was produced at a cost of $822.50, or 27.4 cents per copy, to provide dairy producers, feed
manufacturers, water management personnel and others interested in phosphorus nutrition and excretion.
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COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, John T.
Woeste, director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the
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