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Florida Nutrition Conference
Florida Feed Association
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Sponsored by the Florida Feed Association and the Institute of Food and Agricultural Sciences, University of Florida.

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Presented at the 28th


Sponsored by the

Florida Feed Association

and the

Institute of Food and Agricultural Sciences
University of Florida

November 4 & 5, 1971

University Inn
Gainesville, Florida




Toxic Seeds in Florida-Grown Corn
Dr. Charles F. Simpson, Dr. R. H. Harms, and Dr. B. L. Damron 1

Recycling of Animal Waste by Feeding
Dr. J. P. Fontenot

Modern Concepts of Mineral Needs of Dairy Cattle
Dr. Barney Harris 4

University of Florida Horse Research Center
Mr. J. R. Kilcrease 9

The Use and Value of Mold Inhibitors in Animal Feeds
Dr. Max L. Cooley 11

Methods of Self-Feeding Gestating Sows and Gilts
Dr. Richard Houser 14

Calcium and Phosphorus Requirements of Horses
Dr. E. A. Ott 15

Low Magnesium Tetany in Beef Cattle
Dr. J. P. Fontenot 17

Scare Stories Threaten Use of Feed Additives
Dr. T. J. Cunha. 19

Marek's Vaccine
Dr. G. W. Myerholz 22

Its Impact on Egg Production and Prices
Dr. Ralph A. Eastwood 23

Recent Developments for Improving Egg Shell Quality
Dr. David A. Roland 24


Charles F. Simpson, R. H. Harms, and B. L. Damron
Departments of Veterinary Science and Poultry Science
IFAS, University of Florida, Gainesville

The presence of 2 kinds of seeds in Florida-grown corn is of
practical importance because each seed type can cause mortality,
decreased weight gains or both when consumed in sufficient quantities
by livestock.

It has been known for at least 30 years that the seeds of
Crotalaria spectabilis (showy crotalaria) are highly toxic to all types
of livestock. Two types of crotalaria poisoning are recognized.
Animals die shortly after consumption of seeds (acute poisoning),
or death occurs 2 to 6 months after seeds are consumed (chronic
poisoning). The post-mortem lesions of crotalaria poisoning are
characteristic; they include hemorrhage and accumulation of fluid in
tissues or the body cavities. The number of seeds required to produce
toxicity in chickens has been determined, but this precise information
is not known for other animal species. In chickens, and probably
other animals, there is increasing resistance to crotalaria poisoning
with increasing age. The toxic principal of crotalaria has been

Recently, in 1967, it was determined that consumption of coffee
weed seeds (Cassia occidentalis) by cattle in Florida results in
mortality or sickness. Cases of poisoning in cattle usually occur
after a frost, and are characterized by muscular weakness and trembling,
and passage of dark-colored urine. Vitamin E or selenium does not
seem to be beneficial for treatment. A high percentage of chicks fed
4% C. occidentalis seeds in the diet die, but only a few chicks fed
2% seed die. There are significant weight losses among chicks fed
either 4 or 2% seed. Hens fed these seed go out of production and lose
weight, but only a low percentage die.

Preliminary observations indicate that consumption of Cassia
obtusifolia by chicks interferes with normal weight gains.


J. P. Fontenot
Department of Animal Science
Virginia Polytechnic Institute and State University
Blacksburg, Virginia

Animal wastes have been used mainly as fertilizer, but economic
studies indicate that the plant nutrient value of these materials
is not sufficient to justify cost of handling. An alternative and
perhaps a more economical approach would be the use of these wastes
as animal feed.

Research with wastes from different species of farm animals shows
that these possess substantial nutritional value for certain phases of
animal production. At Auburn University satisfactory performance has
been obtained in cattle fed wastelage, made from hay and cattle manure,
as part of the ration. Gains and feed efficiency in swine were not
appreciably affected in studies at the University of Illinois by in-
cluding 15% dried swine feces in the ration.

A major portion of the research efforts in feeding animal wastes
has been conducted using poultry waste. Research has been conducted
in several states. Poultry waste, including 1) excreta collected from
caged birds, and 2) poultry litter, consisting of excreta, the base litter
material and wasted feed, hns been used in experimental work. Poultry
waste has been shown to contain substantial levels of certain nutrients,
especially nitrogen, calcium and phosphorus. A considerable portion of
the nitrogen is in the form of non-protein nitrogen. Ruminants are
able to utilize non-protein nitrogen, by virtue of the large number of
microbes in the rumen-reticulum. it has been shown that the nitrogen
and energy in poultry waste are efficiently utilized by ruminants.
For example, we found that the energy valid of broiler litter (60% TDN,
dry basis) compared favorably with that of alfalfa hay and the digestible
protein value (23%, dry basis) was higher than for alfalfa hay. There
is considerable variability in chemical composition of animal wastes
even within a given type of waste. The practice of analyzing each lot
of feed followed by the more progressive farmers to solve the problem
of variation in composition of forages, could be used to solve this

Satisfactory animal performance has generally been observed from
feeding animal wastes. For examnle, in Virginia, up to 25% broiler
litter has been included in fattening mixtures for beef cattle with no
consistent effect on performance and feed intake. When the level was
increased to 50%, feed intake and performance were reduced.

Feeding animal wastes has not been shown to adversely affect the
taste of the animal products. Virginia research workers found that

taste of the meat was not adversely affected by feeding steers rations
containing up to 50% broiler litter. Michigan researchers found no
adverse effect on taste of eggs from incorporation of up to 30% dried
poultry waste from caged pullets into the diet of caged layers.

Usually, no serious trouble with animal health has been encountered
from feeding the wastes. One exception was the copper toxicity in
sheep reported by Virginia researchers from feeding broiler litter from
chicks which had been fed high levels of copper sulfate.

Feeding of poultry litter is not sanctioned by U.S.D.A. or F.D.A.
due to potential hazards from drugs and disease organisms. We have
found that broiler litter can be pasteurized by dry heating the litter
at 3020F at a thickness of 1/2 inch for 30 minutes. The test used to
assess the effectiveness of processing is the same as for pasteurized
milk, in which the criteria are less than 10 coliforms and less than
a total of 20,000 bacteria per gram by plate count. Preliminary results
indicate that a combination of chemical and heat treatments may be more
effective than heat treatment alone. Heat treatment was found to result
in substantial nitrogen loss, which could be reduced by acidifying prior
to heat processing. Research results from Virginia showed that there
was no pesticide residue problem in broiler litter. Perhaps the only
major area of research which needs to be pursued before litter can be
considered safe as feed for cattle and sheep is the problem of medicinal
drug residues.


Dr. B. Harris, Jr.
Extension Dairy Nutritionist
IFAS, University of Florida, Gainesville

The mineral elements constitute from 4 to 6% or a relatively small
amount of the total body. Even so, they are essential to many vital
processes. Mineral elements give rigidity and strength to the skeletal
structures. They are constituents of the proteins, and lipids that
make up the muscles, organs, blood cells, and other soft tissues of the
body. They are necessary for the activation of many enzyme systems
and the activities of electrolytes in acid-base regulation. Certain
mineral elements, principally sodium and potassium, are the major
factors in osmotic control of water metabolism. Other minerals are
an integral part of important physiologic compounds such as iodine
in thyroxine, iron in hemoglobin, zinc in insulin, cobalt in vitamin
B12, sulfur in thiamine, biotin, coenzyme A, and lipoic acid. More
detailed functions will be discussed under each mineral element.

The animal body requires seven principal mineral elements:
calcium, phosphorus, magnesium, sodium, potassium, sulfur, and chlorine.
These minerals constitute 60 to 80% of all the inorganic material in
the body. Other minerals used in trace quantities in the body are
iron, copper, cobalt, iodine, manganese, zinc, molybdenum, selenium,
and possibly chromium and fluorine.

Major Minerals

It is of utmost importance that the dairy ration be balanced in
calcium and phosphorus. This is usually accomplished by a simple
calculation and the selection of the proper calcium and phosphorus
supplement. A number of supplements are available in Florida, and
a good supplement or a commercial mineral mixture may be used to
provide the proper ratio and amount of calcium and phosphorus.

The chief function of calcium in the body is for bone formation.
Calcium is also necessary for blood coagulation, in the function of the
heart, muscles and nerves, and in the permeability of membranes. The
optimum level of calcium needed in dairy rations for high levels of
production based on the 1971 NRC recommendations is 0.53% or more
calcium, and preferably less than 1%. The true absorption of dietary
calcium appears to be on the order of about 35%. Milk contains about
0.54 gms. of calcium per pound, or .119%.

Phosphorus has a number of functions in addition to giving strength
and rigidity to bones. It is essential for efficiency in feed

utilization, growth, reproduction and in the transfer, storage and
utilization of energy within the body. Borderline symptoms generally
observed are poor feed utilization, breeding problems, lowered milk
production and increased incidence of milk fever. While it is difficult
to diagnose borderline deficiencies of phosphorus, several tests can
be made that give a fair degree of accuracy. Common tests include the
calculation of ration composition, actual performance of the cattle,
and chemical determination of plasma inorganic phosphorus. Generally,
a simple calculation of grain composition is adequate. The total
ration (dry matter basis) should contain 0.4% or more phosphorus and the
grain mixture about 0.45% or more. The combined requirements of
calcium and phosphorus may be obtained from the 1971 NRC Recommendations
pamphlet (Fourth Revised Edition).

Supplemental salt is a constant need for all livestock. In many
cases, it may serve as an effective carrier for trace minerals.
Because of its importance, we consider it desirable to add from 0.50%
to 1% salt to concentrate mixtures and complete feeds. Allowing dry
cows and heifers free access to salt is a satisfactory way of meeting
their requirements.

Trace Minerals

The 1971 Revision of the National Research Council (NRC) Require-
ments of Dairy Cattle represents an updating of the earlier report
based on newer research results. A new table has been added on the
nutrient content of rations which gives guidelines for trace minerals.
The NRC committee stresses a need for additional research to define
more accurately the trace minerals needs over long periods of time.
Table shows the present recommendations.

Ingredients Quantity per lb. Quantity per ton
Dry Matter As Fed* Dry Matter As Fed*
Min. Min. Min. Min.
Magnesium (g) 0.455 0.500 (lb) 2.0 2.23
Potassium (g) 3.182 3.545 (Ib) 14.0 15.60
Sulfur (g) 0.909 1.000 (Ib) 4.0 4.40
Iron (mg) 45.455 50.455 (g) 91.0 101.00
Cobalt (mg) 0.045 0.050 (g) 0.091 0.101
Copper (mg) 4.454 5.045 (g) 9.1 10.10
Manganese (mg) 9.091 10.000 (g) 18.1 20.20
Zinc (mg) 18.182 20.000 (g) 36.4 40.40
Iodine (mg) 0.273 0.305 (g) 0.54 0.61
Calcium (g) 2.136 2.364 (g) 9.4 10.4
Phos (g) 1.591 1.773 (Ib) 7.0 7.8

*Assumed dry matter 90%

Terminology used in describing symptoms of a magnesium deficiency
are "grass tetany", "grass-staggers", and "Wheat pasture poisoning".
As the names imply, the abnormality is more common in animals grazing
small-grain pastures in early spring. The incidence may be increased
following heavy nitrogen fertilization of pastures. Apparently,
increased production of ammonia in the rumen causes a reduced magnesium
absorption. Also, high levels of calcium and phosphorus may affect
the requirements for magnesium.

It is doubtful if dairy cows consuming adequate levels of concen-
trate would suffer a magnesium deficiency. However, should such a
problem occur, the addition of three to five pounds of magnesium oxide
per ton of feed would provide for the additional actual magnesium
required for high producing cows. The magnesium requirement of dairy
calves is 6 to 14 mg. per pound of body weight per day. The NRC
Requirement for Dairy Cattle suggests a magnesium level of 0.1%
of the ration dry matter.

Because of the high level of potassium found in most feedstuffs,
the potassium requirements of dairy cattle have not been critically
measured. The optimum level for growing and finishing steers has
been reported to be 0.6 to 0.8% of ration dry matter. This level
should be more than adequate for dairy cattle.

There is increasing evidence that sulfur may be limiting in
certain diets. With the increased use of urea in dairy rations, it
has been suggested that supplementation with inorganic sulfate may
be desirable.

The sulfur requirements of ruminant animals is often expressed
in terms of nitrogen-to-sulfur ratios.

Florida soils are known to contain high amounts of sulfur. This,
coupled with the fact that most feedstuffs contain more than 0.1%
sulfur, makes it unlikely that additional supplemental sulfur is
needed, especially when animals are grazing forages. The overall
ration should contain from 0.12% to 0.20% sulfur on a dry matter basis.

Little information is available concerning the minimum require-
ments of iodine. We do know, however, that the levels must be high
enough to prevent goiter. The lack of iodine in the ration is the
principal cause of goiter in all newborn animals. The use of iodized
salt containing 0.015% iodine incorporated at a 1% level of the
grain ration has proved effective in preventing goiters. The use of
stabilized iodine is recommended as a supplement to the ration of

pregnant cows on farms where goiter has been known to occur among
newborn calves. Since the thyroid gland has considerable capacity
for storing iodine, iodine need not be supplemented continuously.

There has been no evidence to date that Florida dairymen need
be concerned with supplementing dairy rations with iodine.

Zinc has been shown to be a dietary essential for ruminants, but
the requirements for dairy cattle have not been established. Most
work available, however, indicates that the ration should contain
approximately 50 ppm or more zinc. Zinc deficiencies have not been
reported in Florida dairy herds. Trace-mineralized salt containing
added zinc as zinc chloride, sulfate, or oxide should provide any
additional needs. Most concentrate mixtures contain from 30 to 50
ppm zinc. A grain mixture containing 50 ppm is equal to 0.005% zinc
by weight.

Studies with dairy cattle indicate that 20-30 ppm (9 to 13 mg.
per pound) of manganese in the diet met the requirement with a
margin of safety. Since most dairy rations contain levels of
manganese in excess of the suggested requirement, it seems unlikely
that further supplementation is needed. Toxic effects may be
obtained with extremely high levels of manganese.

Iron is essential in maintaining a normal level of hemoglobin in
the blood. Also, a deficiency of copper or cobalt or even parasite
infestation, may cause lower levels of hemoglobin in the blood.
Generally, the additional needs for iron can be supplied by adding to
the ration 1% trace mineral salt or other mineral mixture containing
0.5% or more iron. Since iron must be in the ferrous state to be
absorbed, it is generally believed that the ferrous salts of carbonate,
sulfate, and chloride are more biologically available than ferric

In most cases, copper-containing trace mineral salt provides all
the additional copper that high producing dairy cows need. In areas
where rations contain high levels of molybdenum and sulfate, the
copper requirement may be increased two- or three-fold. Copper can be
provided conveniently in deficient areas by adding copper sulfate to
the salt at the rate of about 0.5%.

Mineral Management

A frequently asked question is how best to provide minerals for
dairy animals to assure adequate intake. The answer to this question
varies, depending on the type of ration, the age of the animals,

and the facilities available. In general, milking cows should receive
their minerals in the grain mixture, sometimes called force-feeding
of the minerals. This assures adequate intake of minerals provided
the ration is properly balanced in minerals. Additional minerals,
except perhaps salt, are not needed on the outside in mineral boxes
if provided in the grain mixture. Since salt consumption may vary
with animals, it is a common practice to supply additional salt.
However, do not be concerned if very little is consumed on the outside.

Dry cows and heifers may need additional minerals on the outside.
This is especially true where little grain is being fed due to
maximum utilization of forages. In such instances, a complete mineral
mix containing 30-50% salt, 10-14% phosphorus, 12-16% calcium, and
trace minerals is frequently used. Some dairymen practice mixing
40 to 50% trace mineral salt with 50 to 60% defluorinated phosphate
to give them the desirable combination while others prefer to purchase
a commercial mineral mix. Mineral appetizers should not be added to
increase consumption. Dry cows and heifers will tend to consume
amounts needed each day.


J. R. Kilcrease, Center Manager
Department of Animal Science
IFAS, University of Florida, Gainesville

The University of Florida Horse Research Center consists of 306
acres of land in Marion County, appropriated by the 1969 State
Legislature from holdings of the Florida Correctional Institute at
Lowell. Dr. E. A. Ott, an Animal Nutritionist, will supervise the
development and operation of the Center. Construction and development
of facilities are underway with this year's appropriation of $365,000
by the Legislature.

Research at the Center will concern the major problems encountered
by the horse industry in Florida and will be focused on the following:

1) Nutritional factors influencing growth and sound bone

2) Inproving reproductive efficiency.

3) Controlling disease and parasite problems.

4) The influence of exercise on the nutritional requirements
of the horse.

Facilities will be available for both basic and applied research.
The basic research will concentrate mainly on nutrition and physiology
of reproduction. The applied programs will utilize two bands of
mares, one Thoroughbred and one Quarter Horse, for studies on the
practical application of basic information to breeding and production
programs. Areas of interest include forage utilization, feeding
systems, breeding management, and disease and parasite control programs.
Foals produced by these mares will be used primarily for studies on
factors influencing growth and development. Basic research on disease
and parasite control programs will be conducted at facilities to be
included in the new College of Veterinary Medicine.

While the Horse Research Center will be devoted mainly to research,
it will also have an active educational program. Forty acres have
been set aside as a teaching and extension unit. This facility will be
used for undergraduate and graduate programs in Animal Science,
vocational training and extension programs (including adult education,
youth activities, clinics and short courses). A rehabilitation program


in cooperation with the Florida Correctional Institute at Lowell is
also planned. The planned purpose of this program will be to train
inmates for gainful employment in the horse industry upon their release.

In the next few years, the Horse Research Center can become the
most outstanding facility of its type in the world. As such it will
play an important role in support of Florida's horse industry.


Maxwell L. Cooley
Hoffman-Taff, Inc.
Springfield, Missouri

The importance of the problem of molds and fungi in feeds has been
emphasized and discussed in a multitude of references.

Molds and the mold toxin problems have motivated extensive research
work in an attempt to eliminate or at least control the situation when
difficulties arise. The extent of this research can be appraised by
the fact that over 900 papers are listed in an aflatoxin bibliography;
and there are several hundred more references available on the subject
since that bibliography was prepared.

Increased mold problems are caused by:

1. Corn that is harvested at a higher moisture content than it
was a number of years ago; this wet corn furnishes an
excellent environment for mold growth.

2. Use of bulk feed tanks and mechanized handling of feed and
ingredients permits accumulations of caked material which
encourages mold formation.

3. Damp litter in a poultry house, with a build-up of turkey and
chicken droppings promotes proliferation of certain species
of fungi.

4. Indiscriminate and prolonged use of antibiotics suppresses the
growth of intestinal bacteria but not that of molds and fungi.
The latter tend to grow uncontrolled and may become pathogenic.

5. Poor sanitation of drinking water and feed and other inferior
management practices contribute to the development of mold

Molds and mold toxins are recognized as substantial problems and
are causes of potential profit losses to raisers of poultry and live-
stock. Unfortunately, they are often insidious in their effect and
frequently go unrecognized.

Fungal growths and resulting toxins in feeds weaken birds and
animals, cause decreased growth, depress feed consumption and con-
version, and impair egg production.

Recommendations for combatting mold problems include: use of a
mold inhibitor in the feed; use of low moisture ingredients; keeping
tanks and handling equipment clean; applying good sanitation practices,
and use of either Nystatin or Copper Sulfate to control Mycosis.

In regard to mold inhibitors, the antifungal agent requirement
varies with the pH of the feed. Ten agents are available for the
inhibition of growth of the mold cultures Chaetomium globosum,
Alterneria solani, Penicillium citrinum, and Aspergillus niger at
various pH levels.

Following are the antifungal agents tested,
costs of most of them:

Sodium benzoate

Sodium salicylate

Methyl Paraben (methyl p-hydroxybenzoate)

with approximate

$0.39 per lb.

$1.00 per lb.

$1.97 per lb.

Ethyl p-hydroxybenzoate

Propyl Paraben propyll p-hydroxybenzoate)

Butyl p-hydroxybenzoate

Calcium or sodium propionate

Sorbic acid


Ethyl vanillin

$2.37 per lb.

$0.26 per lb.

$1.55 per lb.

$3.97 per lb.

$7.75 per lb.

The sodium salts of certain of the acids were used to make them
soluble. The data indicate all the compounds are good mold inhibitors
in an acid environment but lose their efficacy at higher pH.

Calcium propionate and sodium propionate sell at the same price
per pound and equally effective as mold inhibitors. However, sodium
propionate cakes and lumps quite readily so calcium propionate is
preferred for feed use. The propionates in an acid environment are
practically equivalent to propionic acid in effectiveness.


It is concluded that there are several antifungal agents that
might be used in feeds to control mold growth. However, because low
cost for such an additive in feeds is of utmost importance it appears
that calcium and sodium propionate are the least expensive mold in-
hibitors to use in feeds even though higher levels are required than for
some of the other compounds (the comparable costs are $0.26 per pound
for the propionates vs. $1.50 to over $2.00 per pound for some of the
other fungal agents).

The recommended levels of the propionates to use are 2 to 5
pounds per ton of feed.


R. H. Houser
Asst. Prof., Suwannee Station
IFAS, University of Florida, Live Oak

Work at many experiment stations has shown that sows will produce
larger litters if their energy intake is limited during gestation than
if they are allowed access to a self-feeder. Overfatness often decreases
litter size, while it increases feed cost. A method of feeding being
used by many producers, that of allowing gestating animals access to

self-feeders for a limited number of hours, either every third day or
Monday, Wednesday, and Friday was evaluated at the Agricultural Research
Center Swine Unit at Live Oak.
Sows and gilts were allowed to eat as much as they would consume
during a 6 hour period, either every third day or on Monday, Wednesday and
Friday. In three experiments production performance for these sows was
as satisfactory as the performance of the control groups of sows and gilts

which were hand-fed each day. Sows and gilts allowed to self-feed 6 hours
Monday, Wednesday, and Friday consumed excess feed, but did not gain
excessively. It appeared that this excess feed consumption could be
controlled by the amount of time allowed for self-feeding. It may be
concluded from this and other studies that these two methods of self-feeding
gestating sows and gilts may be used satisfactorily when proper
management is employed.


E. A. Ott
Assoc. Prof. of Animal Nutrition
IFAS, University of Florida, Gainesville

In formulating horse rations, calcium and phosphorus are two of
the most critical factors to consider. Requirements are apparently
linked directly to the age of the animals and the activities it is
performing. Classical rickets is not commonly observed in horses
receiving inadequate levels of these minerals, however, other bone
abnormalities apparently associated with inadequate mineralization or
demineralization are common. On the basis of available research,
the following requirements are suggested:

Recommended Minimum Daily Calcium and Phosphorus Intake

(Air Dry) (1100 lb Mature Weight)




















Mature Horse at Work:

Light work (2hr/day)

Medium work (2hr/day)


Last quarter of gestation

Peak lactation









In calculating the alcium and phosphorus levels for a grain
ration, the amount of these minerals provided by a ailable forage
must be considered.

Of equal importance to the minimum requirements is the ratio of
calcium to phosphorus in the total ration. The following guidelines are

Calcium to Phosphorus Rations for Complete Rations




Nursing Foal



Long Yearling

1:1 5.0:1











J. P. Fontenot
Department of Animal Science
Virginia Polytechnic Institute and State University
Blacksburg, Virginia

Hypomagnesemic tetany is also known as grass tetany, grass staggers,
lactation tetany, wheat pasture poisoning and winter tetany. A small
percentage of the adult ruminant population is affected with the disturbance.
However, the incidence in individual herds may be quite high, resulting
in severe financial losses. In the U.S. the disturbance generally
occurs in beef cows nursing calves, and is most prevalent during the
early stages of lactation. Older cows seem to be more susceptible than
younger ones.

Usually, the cows suffering from hypomagnesemic tetany have a low
blood serum magnesium level. The physical symptoms are undue excitability
incoordination, loss of appetite, viciousness, muscular twitching, profuse
salivation, grinding of teeth, general tetanic contractions, labored
breathing, pounding heart beat, convulsions and death.

It appears that hypomagnesemic tetany may result from either a
deficiency or poor utilization of magnesium. A deficiency of magnesium
may result from low magnesium in the feed or a low feed intake. Some
forages may be quite low in magnesium. In field studies in Virginia we
observed a relationship between the magnesium content of the forage and
the level of blood serum magnesium.

Results obtained from research at Virginia Tech indicate that the
magnesium requirement is higher for beef cows during lactation than
during gestation. Approximately 0.2% magnesium, dry basis, was needed in
the ration of lactating beef cows in order to maintain blood serum
magnesium levels of 2.0 mg per 100 ml. In gestating beef cows the level
of magnesium needed to maintain normal blood serum magnesium levels
(2.0 mg. per 100 ml.) was about 0.1%, dry basis.

Certain dietary factors may affect magnesium utilization. Generally,
fertilizing with high levels of nitrogen and/or potassium results in
lowered blood serum magnesium levels. Tetany seems to be more of a
problem in cattle grazing heavily fertilized pastures. Cattle grazing
cereal forages, which are usually high in crude protein (nitrogen) and
potassium, seem to be especially susceptible to grass tetany. Thus, it
would appear that levels of crude protein and potassium in the ration or
forage are involved in hypomagnesemic tetany. Oklahoma researchers found
that feeding rations high in crude protein and potassium lowered magnesium
absorption in ruminants. From subsequent research in Virginia it appears
that dietary potassium level is more important than crude protein level.

A sizeable amount of the phosphorus in plants is in the phytate
form. In non-ruminants,feeding high levels of phytic acid appears to
decrease magnesium absorption. In ruminants, form of phosphorus has
not been found to consistently affect magnesium absorption.

In certain parts of the West, there is high incidence of grass
tetany in cattle grazing range plants high in trans-aconitic acid.
Workers from Nevada and USDA produced typical symptoms of hypomagnesemic
tetany in mature cows by drenching high levels of potassium chloride
and trans-aconitic or citric acid.

Since it appears that the cause of hypomagnesemic tetany in cattle
is a metabolic deficiency of magnesium, resulting from a simple mag-
nesium deficiency or inference with magnesium utilization, magnesium
supplementation should be effective in preventing the disturbance. Mag-
nesium supplementation is recommended for prevention of grass tetany
in several states. The recommended level varies among states. A good
source of supplemental magnesium is magnesium oxide. It is high in
magnesium and the availability of magnesium from this source is good.
We found that the availability of magnesium from dolomitic limestone was
quite low, 14%, compared to 51% for magnesium oxide.

Supplemental magnesium can be supplied by force-feeding the
concentrate or silage or by allowing the cattle access to a mineral mix-
ture containing high levels of magnesium. It is important that the
mixture be palatable in order to get optimum magnesium intakes in the


Tony J. Cunha, Chairman
Department of Animal Science
IFAS University of Florida, Gainesville

Scientific facts and objectivity, and not scare stories,
should decide the use of feed additives in animal rations.

We should not continue to allow the public to be misled with
erroneous stories citing fragments of information or giving only
a few questionable facts to prove their point. As a result, we
are going through a period in which people are being confused
with communications that in many cases have no scientific basis

The National Academy of Sciences' National Research Council
organized a symposium in 1967 on the "Use of drugs in animal feeds."
A summary of the reviews given indicates that antibiotics continue
to provide substantial economic benefits to the producer and con-
sumer of meat, milk and eggs. Even after this extensive review
and the overwhelming evidence for the continued use of antibiotics,
there are still a few persons who are again questioning the use
of antibiotics in animal rations.

Dr. T. H. Jukes, of the University of California, recently
stated that "to get an average dose of chloretetracycline commonly
prescribed for home use for patients by physicians, a person would
have to eat one ton of raw chicken meat at a sitting. If the
chickens were taken off feed for a day, the amount of raw chicken
would have to be 10 tons, and if the meat were cooked, the anti-
biotic would be destroyed". This example indicates the reason why
scientists are not concerned about the proper use of antibiotics
in animal feeding.

I am not advocating carelessness in the use of feed additives
or agricultural chemicals. We must treat them with great respect
and make sure their use is safe and that it will not harm the
animal, those feeding the animal, or the human who consumes the

But if agricultural chemicals were banned from use in livestock
feeding, the consumer would be the greatest loser. Let's just
take the example of stilbestrol in cattle feeding. In the feedlot
it can increase rate of gain 18 percent and feed efficiency 12
percent. A ban on its use would increase the price of beef.

In addition we use antibiotics, vitamins, minerals and other
feed additives in making it possible to produce meat at the least
cost possible. At the same time we are continually increasing the
quality, nutritional value and consumer acceptability of the meat
being produced. Our farmers have continually increased their
efficiency of operation to the point that food takes a lesser
percentage of the consumer's take home pay than ever before.

How did we get so efficient in food production? Much of it
traces to the wise use of agricultural chemicals in food production.
If we allow a few persons to panic the consumer into action against
the proper use of agricultural chemicals then we are allowing
"progress to stop" and the "price of food to rise".

There is no doubt that our food is the safest, cleanest and
most wholesome in the world. We do not appreciate the quality and
safety of our food and water until we travel in foreign countries.

I do not mean to imply that we are perfect in all aspects of
food production and protection. We are not. This is why we have
research scientists and others, in every state trying to do an
even better job than has been done heretofore. Both the scientist,
the farmer and others, such as the feed industry, have done an
excellent job to date and will do an even better one in the future.

In the developing countries, where the use of agricultural
chemicals is the lowest in the world, we can find a life span of
about 35 years, about half of what it is in the United States.
This is due, in large part, to a lack of food production which
cannot be increased adequately until agricultural chemicals and
modern technology are used.

As we decide on what needs to be done on environmental control
and the use of agricultural chemicals, we must always keep in mind
the risk-benefit factor. Even though there is the risk of a wreck,
we use our automobiles daily. We also fly in planes, and do many
other things where some risk to life or health is involved. We
do it because we feel the benefits outweigh the risk.

All of us want to breathe clean air, drink pure water and eat
clean, safe food. However, let's decide by scientific facts and
mature judgement across a conference table by scientists and others
what should be done and what standards to set. Let's not allow
these decisions to be made in the press or TV by scare and mislead-
ing stories which frighten and emotionally involve people. Let's
not allow the "alarmists" to poison the climate of opinion and
reason. If we do, we will turn back the calendar and the end result
will be "high priced food", possibly even food shortages.


All of us in responsible positions need to do something about
the scare stories, since the critics and their stories won't just
fade away. Otherwise, much of what the livestock and feed industries
have worked so hard for could vanish by ill-considered and in-
hibitory legislation. Our high standard of living, due in large
part to an abundant food supply, is too precious a privilege to have
destroyed by the unfair critic who uses destructive rather than
constructive criticism and who must think food is produced at
the corner supermarket. We need to be vigilant and quickly answer
and counteract his scare stories with scientific facts.


G. W. Meyerholz
Extension Veterinarian, Department of Veterinary Science
IFAS, University of Florida, Gainesville

Marek's disease is a viral disease of chickens characterized by
the presence of lymphoid tumors of various organs. It is estimated
to cost the poultry industry 200 million dollars annually. Over 39
million chickens were condemned for avian leukosis by Federal meat
inspectors in 1970 and over 75 percent of these losses are attributed
to Marek's disease. The commercial egg industry suffers an average
10 to 20 percent mortality of birds. Economic losses due to lower
egg production have not been determined but may be substantial.

During the past year, commercial vaccines have become available
and other vaccines in the experimental stage offer promise. The
vaccines presently available are produced from a virus isolated from
turkeys that does not produce Marek's disease symptoms or lesions in
chickens or turkeys. The vaccine apparently reduces losses from
Marek's disease 70 to 90 percent in flocks studied through a complete
life cycle. Chickens are usually vaccinated at one day of age at
the hatchery.

The exact mechanism for immunity produced by this vaccine is
unknown. The antigen may have a "sentinel" effect that prevents
damage by future entry of Marek's disease virus. Vaccination does
produce antibodies but infection with the Marek's disease virus does
still occur. However, the virus does little or no damage in most
vaccinated chickens.

Evidence indicates that vaccination with the new vaccine also
results in a reduction of losses due to other infectious diseases.
This can be explained by prevention of damage to the bursa of
Fabricius, a small organ just above the cloaca and a favorite site
for invasion by the Marek's virus. This organ is apparently a neces-
sary part of the chicken's antibody-producing mechanism and prevention
of Marek's disease enables it to function against other infections
of the chicken.

Several aspects need to be considered in vaccination of chickens
for Marek's disease. These include immunity produced, reduction in
disease losses, cost of vaccine, supplies and equipment needed,
and the economic impact on the industry. An understanding of these
factors will give the poultryman an insight into the practical use of
Marek's disease vaccines.



David A. Roland
Asst. Poultry Scientist, Department of Poultry Science
IFAS, University of Florida, Gainesville

Maintaining good egg shell quality is a major concern of the
poultry egg producer. The following series of experiments were
directed toward attaining this goal. In the first experiment four
trials were conducted using a total of 301 mature hens to determine
the effect of calcium source, size, and dosage level on calcium car-
bonate retention in the digestive system. In trials 1, 2, and 4
the hens were either dosed with 10 g/bird or fed free-choice hen or
pullet-sized calcium carbonate derived from oyster shell or limestone.
In trial 3, hens were dosed with either 10 g/bird or 2 g/bird
pullet-sized oyster shell. In all trials the hens were sacrificed at
regular intervals throughout the day, or over a four day period. The
entire digestive system was examined and calcium carbonate retention
in the crop and gizzard determined. The results indicated that
particle size of calcium carbonate (CaCO3) had a definite influence
on CaCO3 retention in the gizzard. However, there were no significant
differences in CaCO3 retention in the gizzard between hens fed
hen-sized CaCO3 or hens fed pullet-sized CaCO3, regardless of whether
the calcium was derived from oyster shell or limestone. The quantity
of CaCO3 dosed seemed to have little influence on the metering of CaCO3
from the gizzard. The results also indicated that 87 percent of the
CaCO metered out of the gizzard in a single 24-hour period was metered
out between 8 a.m. and 8 p.m. with very little of the CaCO3 being
metered out of the gizzard at night.

In the second experiment 585 hens were used in four trials to
determine the effect of various sources and sizes of CaCO3 on egg shell
quality. The results showed that the substitution of hen or
pullet-sized limestone or oyster shell for two-thirds of the pulverized
limestone usually present in a complete laying diet resulted in the
improvement of egg shell quality during hot weather. However, when the
experiment was repeated during cooler weather no beneficial effect on
shell quality was observed. The effect of particle size of CaCO3 on
egg production, serum calcium, feed consumption, and egg weight was

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