Encyclopedia Of Animal Science - N ppsx

Nutrient Management: Diet Modification
Terry J. Klopfenstein
University of Nebraska, Lincoln, Nebraska, U.S.A.
INTRODUCTION
Animal feeding operations are becoming more concen-
trated and the U.S. EPA (Environmental Protection
Agency) has proposed more restrictive requirements.
Great progress has been made in diet modifications
designed to reduce animal excretion of nutrients. The
nutrients of primary concern are nitrogen and phosphorus.
PHOSPHORUS UTILIZATION
Phosphorus (P) is an essential mineral nutrient required
for bone growth and maintenance and for most body
metabolic functions such as energy utilization. Phospho-
rus has been supplemented to animal diets in mineral form
such as dicalcium phosphate produced from mined
mineral deposits. Typically, phosphorus was fed above
the requirement of the animals as a safety factor due to lack
of confidence in the precise P requirements and supplies. P
in manure can build up in soils and subsequently con-
taminate ground water if not properly managed. P require-
ments are quite different for ruminants (cattle and sheep)
and nonruminants (pigs and chickens), and P is metabo-
lized differently by ruminants.
Poultry and swine grow rapidly and therefore require
high levels of P in their diets (up to .6% of diet;
[1–3]
).
Much of the P in feed ingredients (such as corn and
soybean meal) is in the form of phytate P. Swine and
poultry lack the enzyme (phytase) necessary to utilize the

phytate P so it appears in the manure. Inorganic P must be
supplemented to meet the animal’s requirements. This
makes P use very inefficient (10 to 20%) and most of the P
ends up in the manure. There are four technologies that
producers can use to reduce P excretion.
1. Feeding to requirements. Ongoing research is helping
to more precisely define P requirements for each
type of production and for animal ages within each
type of production. With modern technology, it is
possible to formulate diets quite precisely so that P is
not overfed.
[1]
2. Phytase. This enzyme is produced commercially
through microbial fermentations and can be added to
swine or poultry diets. Phytase releases the organic P
from phytate and makes it available to the animal.
[4,5]
Therefore, the phytate P in corn and soybeans, the
primary feedstuffs in swine and poultry diets, is
utilized to meet the animal’s requirements, reducing
the need for supplement.
3. Phase feeding. Swine and poultry grow rapidly. Bone
growth is very rapid in young animals and is
essentially zero in mature animals. Therefore, the
requirement for P decreases as the animals grow and
mature.
[2,3]
Phase feeding is the process of changing
diets to reduce the amount of P. In the past, two or
three diets may have been fed, but now the number is

increasing to five or six. Phase feeding, combined
with precise formulation and precise requirements,
decrease dietary P and therefore manure P.
[1]
4. Low phytate feeds. Genetically enhanced low-phytate
corn and soybean meal are available. The total P in
these feedstuffs is not necessarily lower, but the P is in
the available, inorganic form rather than the organic
(phytate) form.
[1,6]
Feeding low-phytate corn and
soybeans can decrease P excretion by 50%.
Beef and dairy cattle digest and metabolize P somewhat
differently than nonruminants. The microorganisms in the
rumen digest the P in phytate, making the P available to
the animal. Beef and dairy cattle tend to grow slower and
have lower P requirements than nonruminants.
[7,8]
Lac-
tating dairy cows excrete considerable amounts of P in
milk so cows giving milk have higher requirements
higher requirements for higher producers.
[8]
The most important issue with ruminants is to establish
precise requirements and then formulate diets to meet but
not exceed requirements. The requirements for lactating
dairy cows is about .30% of the diet.
[9]
The ingredients
(corn, supplemental protein, silage, alfalfa) fed to dairy

cows will supply most, if not all, of this requirement.
Beef cattle in feedlots are typically fed diets high in
corn grain, which contains .25 to .3% P. Recent research
suggests the requirement for feedlot cattle is .12 to
.14%.
[10]
The problem is that the ingredients in the feedlot
diets (primarily corn) have nearly .3% P. There does not
seem to be any practical way of reducing dietary P levels
below .25% and therefore, P excretion by feedlot cattle is
relatively high.
664 Encyclopedia of Animal Science
DOI: 10.1081/E EAS 120019731
Copyright D 2005 by Marcel Dekker, Inc. All rights reserved.
NITROGEN UTILIZATION
Nitrogen (N) is a part of amino acids (AA) that form
proteins required by all animals; animals consume protein
and AA and then excrete various forms of N. If N in
manure is not managed appropriately, it can contaminate
surface and ground waters (nitrate). Just as important is
the volatilization of N (NH
3
) from manure. The resulting
NH
3
(ammonia) adds to odors and can be redeposited on
cropland or environmentally sensitive areas such as lakes
and streams.
Swine and poultry must be fed essential AAs to meet
requirements. Because of rapid lean growth, AA require-

ments are high and must be met to produce optimal body
weight gains and feed efficiencies.
[2,3]
However, if any
AA is fed above the requirement, that AA will be used for
energy and the N excreted.
IDEAL PROTEIN
The ideal protein is a protein with a balance of amino
acids that exactly meets an animal’s AA requirements.
[11]
By formulating diets to ideal protein content, no excess
AAs are fed and N excretion is minimized. Formulation
for ideal protein can be accomplished by using high-
quality protein sources with good balances of AA and
protein sources that complement the AA balance in corn.
The greatest opportunity is to use crystalline AA to bal-
ance for AA deficiencies. Lowering the dietary protein
content by two percentage points and supplementing with
crystalline AA results in a 20 to 25% decrease in N ex-
cretion in swine or 30 to 40% in poultry.
[12]
FEED ADDITIVES
Feed additives or feeding management systems that in-
crease feed efficiencies also increase efficiency of N uti-
lization. Ractopamine increases lean growth in swine and,
therefore, increases N-use efficiency.
[1]
PHASE FEEDING
Amino acid requirements decrease as swine and poul-
try grow, just as the P requirement decreases. Balancing

diets to ideal protein and changing diets often as pigs or
poultry grow decrease the protein fed and, therefore, the
N excreted.
[1]
NITROGEN FOR RUMINANTS
Cattle are unique because of the microflora in the rumen.
This ability allows them to digest fiber, but does raise
some challenges in protein nutrition. Protein that reaches
the small intestine is a combination of microbial protein
and undegraded feed protein. This protein (metabolizable
protein, MP) is digested and absorbed in a manner similar
to nonruminants. The growing beef animal and lactating
dairy cows have two requirements that nutritionists must
meet degradable protein for the rumen microbes and
undegraded protein that supplies the additional MP
needed by the animal.
[7,8]
Only recently have these
requirements been elucidated, and further refinement of
requirements is needed.
The greatest opportunity for decreasing N excretion by
cattle is to use the MP system to meet but not exceed
requirements for degradable and undegradable protein.
Phase feeding feedlot cattle and group feeding dairy cows
have the potential to markedly reduce N excretion.
Ammonia losses have been reduced by as much as 32%
by using these technologies.
[13]
There is some reluctance
by nutritionists to reduce levels of degradable and

undegradable protein because of concern that milk or
beef production will be compromised. Research indicates
that will not happen, but it is more difficult to control
variables in commercial production facilities.
[14–16]
CONCLUSION
Phosphorus and nitrogen excretion can be reduced
markedly by the use of new technologies. In the future,
there will be incentives for producers and nutritionists to
make use of these technologies.
REFERENCES
1. Klopfenstein, T.J.; Angel, R.; Cromwell, G.L.; Erickson,
G.E.; Fox, D.G.; Parsons, C.; Satter, L.D.; Sutton, A.L.
Animal Diet Modifications to Decrease the Potential for
Nitrogen and Phosphorus Pollution; Council for Agricul
tural Science and Technology: Ames, IA, 2002. CAST
Issue Paper Number 21.
2. National Research Council. Nutrient Requirements of
Poultry, 9th Ed.; National Academy Press: Washington,
DC, 1994.
3. National Research Council. Nutrient Requirements of
Swine, 10th Ed.; National Academy Press: Washington,
DC, 1998.
4. Kornegay, E.T.; Denbrow, D.M.; Yi, Z.; Ravindran, V.
Response of broilers to graded levels of microbial phytase
Nutrient Management: Diet Modification 665
added to maize soybean meal based diets containing three
levels of non phytate phosphorus. Br. J. Nutr. 1996, 75,
839 852.
5. Cromwell, G.L.; Stahly, T.S.; Coffey, R.D.; Monegue,

H.J.; Randolph, J.H. Efficacy of phytase in improving the
bioavailability of phosphorus in soybean meal and corn
soybean meal diets for pigs. J. Anim. Sci. 1993, 71, 1831
1840.
6. Cromwell, G.L.; Traylor, S.L.; White, L.A.; Xavier, E.G.;
Lindemann, M.D.; Sauber, T.E.; Rice, D.W. Effects of
low phytate corn and low oligosaccharide, low phytate
soybean meal in diets on performance, bone traits, and
P excretion by growing pigs. J. Anim. Sci. 2000, 78
(Suppl. 2), 72. (abstract).
7. National Research Council. Nutrient Requirements of Beef
Cattle, 7th Ed.; National Academy Press: Washington, DC,
1996.
8. National Research Council. Nutrient Requirements of
Dairy Cattle, 7th Ed.; National Academy Press: Wash
ington, DC, 2001.
9. Wu, Z.; Satter, L.D.; Blohowiak, A.J.; Stauffacher, R.H.;
Wilson, J.H. Milk production, estimated phosphorus
excretion and bone characteristics of dairy cows fed
different amounts of phosphorus for two or three years.
J. Dairy Sci. 2001, 84, 1738 1748.
10. Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T.; Brink, D.;
Orth, M.W.; Whittet, K.M. Phosphorus requirement of
finishing feedlot calves. J. Anim. Sci. 2002, 80, 1690
1695.
11. Baker, D.H.; Han, Y. Ideal amino acid profile for chicks
during the first three weeks posthatching. Poult. Sci. 1994,
73, 1441 1447.
12. Allee, G.; Liu, H.; Spencer, J.D.; Touchette, K.J.; Frank,
J.W. Effect of Reducing Dietary Protein Level and

Adding Amino Acids on Performance and Nitrogen
Excretion of Early Finishing Barrows. In Proceeding of
the American Association of Swine Veterinarians; Amer
ican Association of Swine Veterinarians: Perry, PA, 2001;
527 533.
13. Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T. Dietary
Protein Effects on Nitrogen Excretion and Volatilization in
Open dirt Feedlots. In Proceedings of the Eighth Interna
tional Symposium on Animals, Agriculture and Food
Processing Wastes; ASAE Press: St. Joseph, MO, 2000;
204 297.
14. Satter, L.D.; Klopfenstein, T.J.; Erickson, G.E. The role of
nutrition in reducing nutrient output from ruminants.
J. Anim. Sci. 2002, 80 (E. Suppl. 2), E143 E156.
15. Klopfenstein, T.J.; Erickson, G.E. Effects of manipulating
protein and phosphorus nutrition of feedlot cattle on
nutrient management and the environment. J. Anim. Sci.
2002, 80 (E Suppl. 2), E106 E114.
16. Wang, S.J.; Fox, D.G.; Cherney, D.J.; Chase, L.E.;
Tedeschi, L.O. Whole herd optimization with the Cornell
net carbohydrate and protein system. III. Application of
an optimization model to evaluate alternatives to reduce
nitrogen and phosphorus mass balance. J. Dairy Sci. 2000,
83, 2160 2169.
666 Nutrient Management: Diet Modification
Nutrient Management: Water Quality/Use
J. L. Hatfield
United States Department of Agriculture, Agricultural Research Service, Ames, Iowa, U.S.A.
INTRODUCTION
Animals generate a valuable source of nutrients in both

organic and inorganic forms. Nutrients in manure can be a
valuable soil amendment; however, if manure is misused,
it can be a potential water quality problem. Water quality
is a primary concern among environmental issues; manure
application is the focus of this article.
MANURE NUTRIENTS
Nutrients vary among species, manure handling, and
storage systems as shown in Table 1. Nutrient content is
affected by species, diet, age, sex, manure storage system,
and length of time in storage. Values shown in Table 1
illustrate the nutrient content in different manure storage
systems but do not represent the full range of variation
within a species or among manure storage systems.
These data provide an indication of the variation
among species and the need for nutrient management
systems to consider animal production systems and
manure storage systems before making assumptions about
the best management system. The goal in nutrient
management is to develop a system in which manure
nutrients may be applied to the soil to supply the crop
needs without being a potential environmental problem.
WATER QUALITY CONCERNS
In nutrient management, water quality concerns focus on
phosphorus (P) and nitrate-nitrogen (NO
3
-N). Broadcast
manure on the soil surface provides for potential surface
runoff conditions, particularly when rain occurs shortly
after application. In a 2001 study, broadcasting manure
resulted in the greatest potential for surface runoff of

soluble P.
[2]
Kleinman and Sharpley
[3]
compared dis-
solved reactive phosphorus from three manures at six rates
under simulated rainfall and found that dissolved reactive
phosphorus loss was related to runoff and manure
application rate. Soluble P losses were a function of the
type of manure, the application rate, and soil type.
Broadcast manure on the soil surface increases the
potential for surface runoff into nearby surface water
bodies. In addition, surface runoff of manure may provide
pathogens that are present in manure a pathway into
nearby water bodies. There are few studies of this problem
and the evidence is insufficient to provide a set of factors
that contribute to pathogen movement.
Incorporation of manure into the soil greatly reduces
the chances of surface runoff. Tabbara
[4]
showed that
incorporation of manure or fertilizer 24 hours before a
heavy rainfall reduced both dissolved reactive P or total P
concentrations by as much as 30% to 60% depending on
the nutrient source and application rate. The incorporation
process moves P below the volume of soil eroded under
high rainfall events. To reduce potential surface losses of
P, manure should be incorporated on soils with intensive
erosive rain, recent extensive tillage, or little or no surface
residue. Incorporation of manure will reduce the likeli-

hood of surface runoff of P and protect surface water from
excess P levels; however, the process of incorporating
manure may increase the potential for sediment loss from
the soil. The development of management practices that
protect soil from surface runoff will decrease potential
losses of manure P into nearby water bodies.
Incorporation of manure may lead to NO
3
-N leaching
because nutrients placed below the surface mixing layer
are in a soil volume where leaching of nutrients can occur.
NO
3
-N present in the manure may be moved into deeper
soil layers by soil water. However, there is no evidence
that this is a direct result of manure application.
Incorporation of manure changes the availability of
nutrients in the soil profile. Nutrients present in manure
are in the organic form and the conversion into available
forms is a function of biological activity and time in the
soil profile. Klausner et al.
[5]
developed a method to
estimate the decay rate for organic nutrients from dairy
manure that has worked well for this species over a range
of environmental conditions. One of the challenges for
manure management is to determine the temporal patterns
of nutrient availability from different manure types and
species. Jokela
[6]

showed that NO
3
-N levels were actually
lower in soils treated with dairy manure compared to
commercial fertilizer because of the slower release of
NO
3
-N from manure.
Nutrient patterns in manured soils can lead to potential
water quality problems; however, these can be managed
through a proper rate of application and incorporation.
Encyclopedia of Animal Science 667
DOI: 10.1081/E EAS 120019732
Published 2005 by Marcel Dekker, Inc. All rights reserved.
Water quality problems can be reduced through relatively
simple management practices that increase nutrient
availability to the crop and decrease the potential for
offsite movement through runoff or leaching.
EFFECT OF MANURE ON SOIL PROPERTIES
RELATED TO WATER QUALITY
Addition of manure to soil causes changes in the soil
properties
[7,8]
that reduces the likelihood of water quality
problems. Water infiltration rate, soil water-holding
capacity, cation exchange capacity, bulk density, organic
matter, biological activity, and plant availability of
nutrients are changed by manure additions. These changes
required at least five years of manure additions to the
soil. A positive impact on water quality is derived from

increased water infiltration rates and water storage ca-
pacity. Surface runoff occurs in soils that quickly develop
a surface seal and ponding begins on the soil surface
leading to the development of small rills that transport
water along the surface. Manure-amended soils have a
larger infiltration rate and more rainfall can enter the soil
before saturation occurs. This change is not a direct ef-
fect of manure addition but a combination of increased
biological activity and organic materials that create a
more stable soil particle that has a higher soil water
content before becoming saturated. The higher water-
holding capacity of soil allows more absorption before the
profile is saturated. Eghball et al.
[9]
concluded that the
increased intensity of rainfall could cause surface runoff
but changes in the soil properties from manure could
offset water quality problems.
Addition of manure to soil not only changes the soil
properties but also restores the soil to a higher level of soil
productivity. Freeze et al.
[10]
found that the applica-
tion of manure to eroded soil was of greater benefit
than application to noneroded soils. Changes in soil
Table 1 Nutrient content in solid and liquid manure for different species and manure handling systems
Species
Solid manure storage Liquid manure storage
Dry matter %
Total N P

2
O
5
K
2
O
Dry matter %
Total N P
2
O
5
K
2
O
(g/kg) (g/l)
Beef 50 10.5 9.0 13.0 9 3.5 2.2 3.1
Dairy 21 4.5 1.5 3.0 8 3.7 1.8 2.3
Poultry 18 19.0 22.5 12.5 10 7.2 5.4 3.6
Swine 76 6.5 4.0 2.5 4 4.3 3.0 2.6
(From Ref. 1.)
Fig. 1 Conceptual diagram of nutrient flows in the MINAS systems for the Netherlands. (Adapted from Ref. 11.)
668 Nutrient Management: Water Quality/Use
properties are more detectable in eroded soils. These
effects of manure can be realized with all sources and
types of manure. Often the water quality problems that
occur in agriculture are from soils that are in a degrad-
ed state and restoration of soil properties will benefit
the environment.
NUTRIENT ACCOUNTING FROM
MANURE SOURCES

To achieve water quality goals and manure application
requires the proper amount of nutrients added to the soil to
supply crop requirements. The components in a nutrient
budget are rates of crop removal, change in the soil
nutrient content, and amount supplied from manure. In the
Netherlands, nutrient accounting systems have been
developed for livestock and cropping systems. Ondersteijn
et al.
[11]
described the mineral accounting system
(MINAS) and provided a framework for nutrient account-
ing (Fig. 1). Manure that is produced is accounted for
through the MINAS approach to ensure that both an
economic and environmental quality goal is achieved.
Development of nutrient management guidelines for
producers to help guide their decisions can have a positive
impact on environmental quality.
CONCLUSION
Nutrient management programs must have a positive
impact on water quality. The challenge for producers is to
understand the nutrient balance in the soil and to reduce
the risk of surface runoff of manure. The challenge for
science is to increase our understanding of the value of
manure in the soil and in the restoration of eroded soils to
a higher level of productivity. Improved methods for
sampling manure to determine the nutrient content from
individual farms and for manure application that incor-
porates manure to reduce erosion and enhance the value of
manure on soil properties will benefit livestock, crop
producers, and the environment.

REFERENCES
1. MWPS (MidWest Plan Service). Manure Storages. Ma
nure Management System Series. MWPS 18, Section 2.
MidWest Plan Service. Iowa State University: Ames, IA,
50011 3080, 2001.
2. Zhao, S.L.; Gupta, S.C.; Huggins, D.R.; Moncrief, J.F.
Tillage and nutrient source effects on surface and
subsurface water quality at corn planting. J. Environ. Qual.
2001, 30, 998 1008.
3. Kleinman, P.J.A.; Sharpley, A.N. Effect of broadcast
manure on runoff phosphorus concentrations over succes
sive rainfall events. J. Environ. Qual. 2003, 32, 1072 1081.
4. Tabbara, H. Phosphorus loss to runoff water twenty four
hours after application of liquid swine manure or fertilizer.
J. Environ. Qual. 2003, 32, 1044 1052.
5. Klausner, S.D.; Kanneganti, V.R.; Bouldin, D.R. An
approach for estimating a decay series for organic nitrogen
in animal manure. Agron. J. 1994, 86, 897 903.
6. Jokela, W.E. Nitrogen fertilizer and dairy manure effects
on corn yield and soil nitrate. Soil Sci. Soc. Am. J. 1992,
56, 148 154.
7. Sommerfeldt, T.G.; Chang, C. Changes in soil properties
under annual applications of feedlot manure and different
tillage practices. Soil Sci. Soc. Am. J. 1985, 49, 983 987.
8. Sommerfeldt, T.G.; Chang, C. Soil water properties as
affected by twelve annual applications of cattle feedlot
manure. Soil Sci. Soc. Am. J. 1987, 51, 7 9.
9. Eghball, B.; Gilley, J.E.; Baltensperger, D.D.; Blumenthal,
J.M. Long term manure and fertilizer application effects on
phosphorus and nitrogen in runoff. Trans. ASAE 2002, 45,

687 694.
10. Freeze, B.S.; Webber, C.; Lindwall, C.W.; Dormaar, J.F.
Risk simulation of the economics of manure application to
restore eroded wheat cropland. Can. J. Soil Sci. 1993, 87,
267 274.
11. Ondersteijn, C.J.M.; Beldman, A.C.G.; Daatselaar, C.H.G.;
Giesen, G.W.J.; Huirne, R.B.M. The Dutch mineral
accounting systems and the European nitrate directive:
Implications for N and P management and farm perfor
mance. Agric. Ecosyst. Environ. 2002, 92, 283 296.
Nutrient Management: Water Quality/Use 669
Nutrient Requirements: Carnivores
Duane E. Ullrey
Michigan State University, East Lansing, Michigan, U.S.A.
INTRODUCTION
Carnivores, broadly defined, sustain themselves by
feeding on vertebrate or invertebrate animal tissues, a
practice observed in both the animal and plant kingdoms.
The Venus flytrap (Dionaea muscipula), one of over 500
carnivorous plant species, lives in humid, acidic bogs in
the Carolinas and, like most plants, acquires energy and
nutrients by photosynthesis and through the roots. In this
environment, nitrogen and some mineral elements are in
short supply, and these needs are met by capturing insects
attracted to nectar in a specialized leafy trap, functioning
both as a mouth and stomach. Animals, of course, do not
possess roots or the mechanisms of photosynthesis. Thus,
energy and nutrient requirements of wild carnivorous
animals are acquired principally by consuming vertebrate
or invertebrate prey.

[1,2]
Wilson
[3]
estimated there are about 4000 species of
extant mammals, 9000 of birds, 6300 of reptiles, 4200 of
amphibians, and 18,000 of fish and lower chordates. The
nutrient requirements of these species are presumed to be
qualitatively similar, but quantitative nutrient require-
ments have been defined by the National Academy of
Sciences/National Research Council (NAS/NRC) only for
humans and a few domesticated or captive mammals,
birds, and fish. Of the species with NRC-defined require-
ments, the cat, mink, tarsiers, rainbow trout, and salmon
are obligate carnivores. The NRC also has defined the
nutrient requirements of the dog and fox, but these species
appear to be facultative carnivores and may consume
considerable vegetable matter.
CARNIVOROUS MAMMALS
The immediate ancestors of the domestic cat (Felis catus)
were strictly carnivorous, and its needs have been the most
thoroughly studied of any of the obligate carnivores.
Although commercial diets for cats may contain vegetable
matter, the nutrients and the amounts that must be present
reflect a long evolutionary dependence on a strictly
carnivorous diet. The cat has a simple digestive system,
presumably because digestibility of natural prey tends to
be high, and there is no need for extended food retention
and microbial fermentation. Due to its limited ability to
conserve nitrogen, the cat has a high protein requirement,
and it converts only negligible amounts of tryptophan to

niacin (neither ability is necessary when consuming whole
prey). Requirements for blood glucose are met primarily
by gluconeogenesis rather than from dietary carbohydrate,
and the cat has a high requirement for arginine for
disposal of nitrogen via the urea cycle. It requires taurine
and arachidonic acid because of limited tissue synthesis
(vertebrate prey provide adequate amounts), and it is
unable to convert
b-carotene (a plant provitamin) to
vitamin A. Vitamin D
3
needs are met by diet because
cutaneous concentrations of 7-dehydrocholesterol (provi-
tamin D
3
) are insufficient to support vitamin D photobio-
genesis. Nutrient needs of the cat have been reviewed by
the NRC,
[4]
and minimal requirements, adequate intakes,
and recommended allowances have been published. The
NRC-recommended allowances for growth, maintenance,
late gestation, and peak lactation are presented in Table 1.
The mink (Mustela vison) eats small mammals, fish,
frogs, crayfish, insects, worms, and birds in the wild.
Like the cat, its protein requirements are high 38% of
dietary dry matter (DM) from weaning to 13 weeks of
age, 22 26% for adult maintenance, 38% for gestation,
and 46% for lactation.
[5]

Whether the mink shares the
other unique metabolic features of the cat has not
been determined.
Tarsiers (Tarsius spp.) eat insects (beetles, ants,
locusts, cicadas, cockroaches, mantids, moths) and
sometimes small vertebrates in the wild. Although the
quantitative nutrient requirements of tarsiers have not
been specifically defined, estimated adequate nutrient
concentrations in dietary DM have been proposed.
[6]
When kept in captivity, tarsiers are often provided crickets
as a major food item. Because crickets and other
commercially available insects tend to be deficient in
certain nutrients (particularly calcium, vitamin A, and
vitamin D),
[7]
specifically formulated diets are offered to
these insects for about 48 hours before feeding them to
tarsiers so that the insects plus their gut contents will be
nutritionally complete.
[8–10]
Other obligate carnivorous mammals include felids
such as lions, tigers, leopards, cheetahs, and jaguars.
Aquatic mammals such as dolphins, seals, sea lions, and
walruses also are obligate carnivores, but little is known
about their quantitative nutrient requirements.
670 Encyclopedia of Animal Science
DOI: 10.1081/E EAS 120019733
Copyright D 2005 by Marcel Dekker, Inc. All rights reserved.
Table 1 Recommended nutrient allowances in dietary dry matter (DM) for domestic cats consuming diets containing 4 kcal of

metabolizable energy per g of DM
Nutrient Growth Maintenance Late gestation Peak lactation
Crude protein, % 22.5 20.0 21.3 30.0
Arginine, % 0.96 0.77 1.50 1.50
Histidine, % 0.33 0.26 0.43 0.71
Isoleucine, % 0.54 0.43 0.77 1.20
Methionine, % 0.44 0.17 0.50 0.60
Meth.+cystine, % 0.88 0.34 0.90 1.04
Leucine, % 1.28 1.02 1.80 2.00
Lysine, % 0.85 0.34 1.10 1.40
Phenylalanine, % 0.50 0.50
Phenyl.+tyrosine, %
a
1.91 1.53 1.91 1.91
Threonine, % 0.65 0.52 0.89 1.08
Tryptophan, % 0.16 0.13 0.19 0.19
Valine, % 0.64 0.51 1.00 1.20
Taurine, %
b
0.04 0.2 0.04 0.2 0.04 0.2 0.04 0.2
Total fat, % 9.0 9.0 9.0 9.0
Linoleic acid, % 0.55 0.55 0.55 0.55
a Linolenic acid, % 0.02 0.02 0.02
Arachidonic acid, % 0.02 0.004 0.02 0.02
Eicosapentaenoic and
docosahexaenoic acid, %
0.01 0.01 0.01 0.01
Calcium, % 0.80 0.29 1.08 1.08
Phosphorus, % 0.72 0.26 0.76 0.76
Magnesium, % 0.04 0.04 0.06 0.06

Sodium, % 0.14 0.07 0.13 0.13
Potassium, % 0.40 0.52 0.52 0.52
Chloride, % 0.09 0.10 0.20 0.20
Iron, mg/kg 80 80 80 80
Copper, g/kg 8.4 5.0 8.8 8.8
Zinc, mg/kg 75 75 60 60
Manganese, mg/kg 4.8 4.8 7.2 7.2
Selenium, mg/kg 0.4 0.4 0.4 0.4
Iodine, mg/kg 2.2 2.2 2.2 2.2
Vitamin A, IU/kg 3,550 3,550 7,500 7,500
Vitamin D
3
, IU/kg 250 250 250 250
RRR
a tocopherol, mg/kg 38 38 38 38
Vitamin K (menadione), mg/kg 1.0 1.0 1.0 1.0
Thiamin, mg/kg 5.5 5.6 5.5 5.5
Riboflavin, mg/kg 4.25 4.25 4.25 4.25
Pyridoxine, mg/kg 2.50 2.50 2.50 2.50
Niacin, mg/kg 42.5 42.5 42.5 42.5
Pantothenic acid, mg/kg 6.25 6.25 6.25 6.25
Folic acid, mg/kg 0.75 0.75 0.75 0.75
Biotin, mg/kg 75 75 75 75
Vitamin B
12
, mg/kg 22.5 22.5 22.5 22.5
Choline, mg/kg 2,550 2,550 2,550 2,550
a
At least twice as much phenylalanine (or phenylalanine plus tyrosine) is required for maximal black hair color as for growth.
b

Recommended taurine allowances are lowest when diets are unprocessed (0.04% of DM) but are increased by extrusion (0.1% of DM) or canning (0.2%
of DM).
(Adapted from Ref. 4, recommended allowances for growth of an 800 g kitten, maintenance or late gestation of a 4 kg adult cat, and lactation of a 4 kg
queen with four kittens.)
Nutrient Requirements: Carnivores 671
CARNIVOROUS BIRDS
The digestive systems of obligate carnivorous birds (such
as hawks and eagles), like their mammalian counterparts,
do not have compartments adapted for microbial fermen-
tation. Relatively indigestible portions of prey, such as fur,
feathers, bones, fins, scales, shells, and exoskeletons, may
be separated from more digestible portions by the beak
prior to food ingestion. Sometimes, this separation is
accomplished in the gizzard, followed by egestion of
indigestible matter out of the mouth, as in owls.
[11]
Although the NRC
[12]
has defined the nutrient require-
ments of poultry, these species are principally herbivo-
rous. Based on present metabolic evidence and the
composition of vertebrate and invertebrate prey, it seems
likely that nutrient needs of carnivorous birds are similar
to those of carnivorous mammals, with adjustments for
differences in reproductive strategy.
CARNIVOROUS REPTILES
AND AMPHIBIANS
The long evolutionary association of snakes, crocodilians,
and some lizard families with subsistence on vertebrate
and invertebrate prey suggests that they are obligate

carnivores. They tend to have simple gastrointestinal
systems as compared to herbivorous reptiles, although
there are adaptations related to the periodicity of feeding
and to unique characteristics of certain food items.
Tortoises are chiefly herbivorous with a few that are
omnivorous. Turtles tend to be omnivorous carnivorous
as juveniles and herbivorous or omnivorous as adults
although a few species are mostly carnivorous throughout
life.
[13]
Studies that define qualitative or quantitative
needs of reptiles are few, although protein and amino acid
needs of the hatchling green sea turtle (Chelonia mydas;
carnivorous as hatchlings, herbivorous as adults) have
been investigated. Some studies suggest that young red-
eared slider turtles (Trachemys scripta elegans) and green
anoles (Anolis carolinensis) do not have an elevated
requirement for arginine (as does the cat), and addition of
taurine to a diet based on plant proteins does not improve
growth of young American alligators (Alligator missis-
sippiensis). Also, American alligators appear to convert
linoleic acid to arachidonic acid to some extent, although
rates may not be optimum for maximum growth.
[1]
When
a purified diet containing adequate tryptophan but no
niacin was administered weekly by stomach tube to bull
snakes (Pituophis melanoleucus sayi) for 132 days, no
signs of deficiency were seen, suggesting that either a
longer period of depletion is necessary to induce niacin

deficiency or metabolic conversion of tryptophan to niacin
may occur in this species.
[14]
Thus, if these reptiles are
indeed obligate carnivores, their nutrient needs seem to
deviate from those of the cat.
Most amphibians appear to be obligate carnivores.
[13]
Adult frogs and toads consume invertebrates and small
vertebrates, although most species are herbivorous as
larvae (tadpoles) and have a long, coiled intestine
permitting them to digest plant matter. At metamorphosis,
the intestine is much shortened and the diet becomes
strictly carnivorous. Tadpoles of a few species are
carnivorous and have a much shorter gut than do
herbivorous tadpoles. Salamanders and newts are carniv-
orous both as larvae and as adults, feeding on insects,
slugs, snails, and worms. Caecilians (limbless, viviparous
amphibians) prey on worms, termites, and orthopterans.
Metabolic features characteristic of carnivory have not
been well studied in amphibians.
CARNIVOROUS FISH
Rainbow trout (Salmo gairdneri) and coho salmon
(Oncorhynchus kirsutch) have protein requirements of
!40% of dietary DM for maximal growth of juveniles and
have an absolute requirement for arginine. They also lack
the ability to synthesize niacin from tryptophan. Gluco-
neogenesis is important for provision of blood glucose,
and essential fatty acid requirements include linoleic
acid and eicosapentaenoic acid and/or docosahexaenoic

acid.
[15]
CONCLUSIONS
Qualitative and quantitative nutrient requirements of
obligate carnivores generally appear to reflect evolution-
ary adaptations to the composition of ancestral diets.
REFERENCES
1. Allen, M.E.; Oftedal, O.T. The Nutrition of Carnivorous
Reptiles. In Captive Management and Conservation of
Amphibians and Reptiles, Contributions to Herpetology,
Vol. 11; Murphy, J.B., Adler, K., Collins, J.T., Eds.;
Society for the Study of Amphibians and Reptiles: Ithaca,
NY, 1994; 71 82.
2. Allen, M.E.; Oftedal, O.T.; Baer, D.J. The Feeding and
Nutrition of Carnivores. In Wild Mammals in Captivity:
Principles and Techniques; Kleiman, D.G., Allen, M.E.,
Thompson, K.V., Lumpkin, S., Eds.; Univ. Chicago Press:
Chicago, IL, 1996; 139 147.
3. Wilson, E. The Diversity of Life; Harvard Univ. Press:
Cambridge, MA, 1992.
4. National Research Council. Nutrient Requirements of Dogs
672 Nutrient Requirements: Carnivores
and Cats; National Academies Press: Washington, DC,
2004.
5. National Research Council. Nutrient Requirements of Mink
and Foxes, 2nd Rev.; National Academy Press: Wash
ington, DC, 1982.
6. National Research Council. Nutrient Requirements of
Nonhuman Primates, 2nd Rev. Ed.; National Academies
Press: Washington, DC, 2003.

7. Finke, M.D. Complete nutrient composition of commer
cially raised invertebrates used as food for insectivores.
Zoo Biol. 2002, 21, 269 285.
8. Allen, M.E.; Oftedal, O.T. Dietary manipulation of the
calcium content of feed crickets. J. Zoo Wildl. Med. 1989,
20, 26 33.
9. Finke, M.D. Gut loading to enhance the nutrient content of
insects as food for reptiles: A mathematical approach. Zoo
Biol. 2003, 22, 147 162.
10. Roberts, M.; Kohn, F. Habitat use, foraging behavior, and
activity patterns in reproducing Western tarsiers, Tarsius
bancanus, in captivity: A management synthesis. Zoo Biol.
1993, 12, 217 232.
11. Klasing, K.C. Comparative Avian Nutrition; CAB Inter
national: New York, NY, 1998.
12. National Research Council. Nutrient Requirements of
Poultry; National Academy Press: Washington, DC, 1994.
13. The Encyclopedia of Reptiles and Amphibians; Halliday,
T.R., Adler, K., Eds.; Facts on File, Inc.: New York, NY,
1986.
14. Bartkiewicz, S.E.; Ullrey, D.E.; Trapp, A.L.; Ku, P.K. A
preliminary study of niacin needs of the bull snake
(Pituophis melanoleucus sayi). J. Zoo Anim. Med. 1982,
13, 55 58.
15. National Research Council. Nutrient Requirements of Fish;
National Academy Press: Washington, DC, 1993.
Nutrient Requirements: Carnivores 673
Nutrient Requirements: Nonruminant Herbivores
Michael R. Murphy
Amy C. Norman

University of Illinois at Urbana Champaign, Urbana, Illinois, U.S.A.
INTRODUCTION
Nonruminant herbivorous mammals include a small
number of commercially important animals and a larger
number of wild species.
[1]
Digestive strategies clearly
differ among these herbivores. Mammals lack enzymes to
hydrolyze a substantial portion of plant material (cell
walls), but various pregastric (including ruminant) and
postgastric microbial fermentation systems have evolved
that enable herbivorous mammals to utilize fibrous sub-
strates. Digestive strategy and body size data for East
African nonforest herbivores indicated that ruminants
dominated medium body sizes, whereas nonruminants pre-
vailed among very large and small herbivores
[2]
(Fig. 1).
Our objective was to briefly review current knowledge
about the nutritional requirements of nonruminant herbi-
vores. Those for horses (Equus caballus) and domestic
rabbits (Oryctolagus cuniculus) are stressed. Among
commercially important and widely distributed species,
horses and rabbits represent very large and small
mammalian herbivores, respectively. In addition, they
exemplify subgroups of postgastric fermenters that
emphasize colonic (horses) or cecal (rabbits) function.
More detailed information is also available on their
nutritional requirements than for many other species.
HORSES

Water
Horses usually drink 2 to 3 L of water/kg of dry matter
consumed. Water intake increases with lactation, exercise,
and elevated temperatures by 50 to 70%, 20 to 300%, and
up to 300%, respectively. Ad libitum access to fresh, clean
water is recommended except after intense exercise, when
horses should be allowed to drink only small amounts
every 5 to 10 minutes for approximately 1 hour.
[3]
Energy
Horses get most of their dietary energy from carbohy-
drates and lipids. Energy value is usually expressed in
terms of digestible energy (DE, gross energy minus fecal
energy).
[4]
Structural carbohydrates, such as cellulose and
hemicellulose, often make up the majority of their diet
[3]
and are fermented by microbes in the cecum and colon to
provide much of the energy required by a horse at
maintenance.
[4]
A minimum of 12 to 15% fiber is
presumed necessary to minimize incidence of colic and
laminitis, but forages alone do not generally provide
sufficient energy for growing, working, or lactating
horses, so cereal grains are added to their diets. Cereal
grains provide digestible nonstructural carbohydrate
(starch).
[4]

Lipids may also be supplemented, providing
2.25 times the energy value of carbohydrates,
[5]
and 20%
added fat can be included in the diet without adverse
effects.
[4]
Diets supplemented with fat should be moni-
tored closely for rancidity, because spoiled feed is not
accepted. Supplementation with fat improves work output,
reproductive performance, milk production, and foal
growth, but it must be monitored closely to avoid obesity
and insulin resistance.
[4]
Protein
Amino acids, the building blocks of protein, are
required.
[4]
Protein deficiency retards growth of young
horses and causes tissue loss, poor coat, and abnormal
hoof development in the adult. Average protein intake at
maintenance is approximately 0.6 g of digestible protein/
kg/day and should be increased during late gestation and
early lactation. Protein requirements for working horses
have not been clearly defined, but it is not considered
advantageous to feed protein above the maintenance
requirement. High-quality protein is essential for the
growing horse, and it appears that growth is maximal
when the protein-to-energy ratio is 50 and 45 g of crude
protein/Mcal of DE/day for weanlings and yearlings,

respectively. Lysine is the first-limiting amino acid for
growing horses, and there appears to be no beneficial
effect of including nonprotein nitrogen sources in
practical diets for horses.
[4]
Minerals and Vitamins
The major minerals needed by horses are Ca, P, Na, K, Cl,
I, Fe, Cu, Zn, Mg, and Se.
[4]
Bone is approximately 35%
674 Encyclopedia of Animal Science
DOI: 10.1081/E EAS 120019734
Copyright D 2005 by Marcel Dekker, Inc. All rights reserved.
Ca and 16% P. The dietary Ca:P ratio is critical for proper
bone development; ratios less than 1:1 can impair Ca
absorption and cause detrimental bone abnormalities in
developing horses. Sodium, K, and Cl are the three major
minerals involved in electrolyte balance, and it is neces-
sary to maintain proper concentrations of each. Iodine is
important for regulation of metabolism, but it should be
closely monitored because horses are susceptible to iodine
toxicity. Iron is adequate in most diets, so supplementa-
tion is unnecessary, although frequently practiced.
Vitamins are often classified as fat-soluble or water-
soluble. The former category includes vitamins A, D, E,
and K. Vitamin A is important for good vision. Vitamin D
is essential for calcium and phosphorus absorption, but
rarely needs to be supplemented if animals are exposed to
sunlight. Water-soluble thiamin and riboflavin are dis-
cussed in a publication of the National Research Council

(NRC).
[4]
A deficiency of thiamin can cause a multitude
of problems, but neither deficiency nor toxicity of ribo-
flavin has been reported. Requirements for other water-
soluble vitamins (niacin, pantothenic acid, pyridoxine,
biotin, folacin, B
12
, ascorbic acid, and choline) have not
been determined, but they are presumed to be required.
Table 1 summarizes nutrient requirement data for horses.
RABBITS
Mature rabbits vary greatly in size, from 1 to 6 kg.
[6]
Therefore, their nutrient requirements are not usually
specified on an amount-per-day basis, but on a dietary
concentration relative to body size, or relative to meta-
bolic body size basis.
Fig. 1 The relationship between digestive strategy and body
size in 186 species of East African nonforest herbivores.
(Adapted from Ref. 2, with the sizes of rabbits and horses
marked for comparison.) (View this art in color at www.
dekker.com.)
Table 1 Estimated nutrient requirements for a 500 kg mature horse
Nutrient Unit
a
Growth Maintenance Gestation Lactation Work
Water L 23 30 38 45 38 57 38 57 38 68
Energy Mcal of digestible energy 14 19 16.5 18 19 28 24 20 33
Protein g 720 850 656 801 866 1,427 1,048 820 1,300

Minerals
Calcium g 34 29 20 35 37 56 36 25 40
Phosphorus g 19 16 18 26 28 36 22 18 29
Potassium g 11.3 17.8 25 29.1 31.5 46 33 31.2 49.9
Magnesium g 3.7 5.5 7.5 8.7 9.4 10.9 8.6 9.4 15.1
Sulfur % 0.15 0.15 0.15 0.15 0.15
Sodium % 0.1 0.1 0.1 0.1 0.3
Iron mg/kg 50 40 50 50 40
Manganese mg/kg 40 40 40 40 40
Zinc mg/kg 40 40 40 40 40
Copper mg/kg 10 10 10 10 10
Selenium mg/kg 0.1 0.1 0.1 0.1 0.1
Iodine mg/kg 0.1 0.6 0.1 0.6 0.1 0.6 0.1 0.6 0.1 0.6
Cobalt mg/kg 0.1 0.1 0.1 0.1 0.1
Vitamins
A IU/kg 2,000 2,000 3,000 3,000 2,000
D IU/kg 800 300 600 600 300
E IU/kg 80 50 80 80 80
a
Amounts or concentrations on a dry matter basis.
(From Refs. 3 and 4.)
Nutrient Requirements: Nonruminant Herbivores 675
Water
Although the NRC
[6]
did not address the subject of water,
others
[7,8]
have noted that the water requirements of
rabbits fed dry feed far exceed their dry matter intakes.

Consumption of such diets drops precipitously if water is
withheld. Water intake on dry diets is about 120 mL/kg of
rabbit, or twice the amount of feed consumed. Environ-
mental temperature also influences water consumption,
increasing it by 67% between 18 and 308C. High-quality
drinking water should always be available.
Energy
For diets containing 12 to 15% digestible protein, DE and
metabolizable energy (ME, DE minus urinary energy in
nonruminants) are closely correlated, and ME is about
95% of DE. Diet ME and net energy (ME minus heat
increment) contents are more difficult to determine than
DE, so DE values are still commonly used in practical
rabbit feeding.
[8]
Rabbits do not utilize plant fiber as efficiently as
widely assumed
[6]
and coprophagy (consumption of soft
feces of cecal origin) does not appear to greatly influence
the overall efficiency of fiber digestion.
[7]
Cellulose and
hemicellulose digestibilities in rabbits are similar to those
of rats, and less than in horses and guinea pigs. Only about
10% of neutral detergent fiber in timothy hay was digested
by rabbits, compared to about 35% for horses and ponies.
Rabbit growth rate is apparently optimal with diets having
13 to 25% acid detergent fiber. A minimum of 10%
dietary crude fiber is needed to maximize growth rate (and

to prevent enteritis and fur pulling), but over 17%
depresses growth by restricting feed intake.
Starches, sugars, and lipids apparently pose no special
problems for rabbits. The likelihood of a deficiency of
essential fatty acids is remote, but it has been demon-
strated in rabbits.
Protein
Rabbits need adequate quantities of essential amino acids
in their diet for rapid growth, and nonprotein nitrogen
cannot be employed usefully in grower diets.
[6]
Protein
quality must allow essential amino acid requirements to be
met. Required and optimal concentrations of some amino
acids have been established for growing and lactating
rabbits.
[6–8]
Rabbits are able to utilize 64 to 90% of the
crude protein in common feedstuffs.
[7]
They can maintain
positive nitrogen balance when fed gelatin, a protein
devoid of the essential amino acid tryptophan, because of
the consumption of microbial protein via coprophagy.
Negative nitrogen balance occurred when coprophagy
was prevented. Increased feed intakes can compensate
for low protein concentrations in diets. Therefore, it is
desirable to express protein requirements per unit of
energy. Growth is optimized with about 55 mg of crude
protein/kcal of DE.

Minerals and Vitamins
The rabbit is unusual because serum Ca concentration
reflects dietary Ca concentration, rather than being
homeostatically regulated in a narrow range as in other
species.
[6,7]
Hypocalcemia is sometimes observed in
late gestation or early lactation. It is treatable with Ca-
gluconate injection. However, whether an acidotic diet
during late gestation would be prophylactic, as it is
for a dairy cow, is not known.
[8]
Requirements for
many minerals have not been well studied, although
deficiencies and problems with excesses have often
been demonstrated.
Vitamin A deficiency and toxicity have been demon-
strated, but precise requirements have not been deter-
mined.
[7,8]
Any dietary requirement for vitamin D is likely
Table 2 Estimated nutrient requirements for rabbits (amounts
are per kilogram of air dry diet, unless otherwise specified)
Nutrient Unit Growth Lactation
Water kg 1.6 2.0
Energy kcal 2,500 2,500
MJ 10.5 10.5
kJ of digestible
energy/kg
0.75

950 1,200
Protein g 170 180 170 180
Minerals
Calcium g 8 11.8
Phosphorus g 5 6.6
Potassium g 6 9
Sodium g 2 2.2
Chlorine g 3 3.2
Magnesium g 3 3
Iron mg 50 75
Zinc mg 25 50
Copper mg 10 10
Manganese mg 8.5 10
Iodine mg 0.2 0.2
Cobalt mg 0.1 0.1
Selenium mg 0.01 0.01
Vitamins
A IU 6,000 10,000
D IU 1,000 1,000
Emg 3545
Kmg 12
(Mean or median values compiled from Refs. 6 8.)
676 Nutrient Requirements: Nonruminant Herbivores
much lower than for other species. The only practical
problem encountered with vitamin D in rabbit nutrition is
toxicity: 2300 to 3000 IU of vitamin D/kg are detrimental.
Vitamin E deficiency has been demonstrated, but
recommendations are based primarily on old data or
extrapolation from other species. Vitamin K is probably
not of practical concern in rabbit nutrition because it is

synthesized in the cecum, and no requirement studies have
been conducted.
Under practical conditions, B-complex vitamins are
not dietarily essential for rabbits, but deficiencies have
been demonstrated. Addition of B vitamins to commer-
cial rabbit feeds has not shown benefits. Rabbits can
synthesize vitamin C, so it is not a dietary essential
either. In commercial diets, it is advisable to include a
vitamin mixture that provides at least moderate concen-
trations of vitamins A and E to ensure that no deficiency
occurs. Table 2 summarizes nutrient requirement data
for rabbits.
CONCLUSION
Much remains unknown about the nutritional require-
ments of nonruminant herbivores. Current data, how-
ever, allow many practical dietary limitations and tox-
icities to be avoided in commercially important and
widely distributed species, particularly horses and do-
mestic rabbits.
REFERENCES
1. Cork, S.J.; Hume, I.D.; Faichney, G.C. Digestive Strategies
of Nonruminant Herbivores: The Role of the Hindgut. In
Nutritional Ecology of Herbivores; Jung, H. J.G., Fahey,
G.C., Jr., Eds.; Amer. Soc. Anim. Sci.; Savoy: IL, 1999;
210 260.
2. Demment, M.W.; Van Soest, P.J. A nutritional explanation
for body size patterns of ruminant and nonruminant
herbivores. Am. Nat. 1985, 125, 641 672.
3. Lawrence, L. Feeding Horses. In Livestock Feeds and
Feeding, 5th Ed.; Kellems, R.O., Church, D.C., Eds.;

Prentice Hall: Upper Saddle River, NJ, 2002; 381 401.
4. National Research Council. Nutrient Requirements of
Horses, 5th Rev. Ed.; Natl. Acad. Sci.: Washington, DC,
1989.
5. Ensminger, M.E.; Oldfield, J.E.; Heinemann, W.W. Feeds
and Nutrition, 2nd Ed.; Ensminger Publ. Co.: Clovis, CA,
1990.
6. National Research Council. Nutrient Requirements of Rab
bits, 2nd Rev. Ed.; Natl. Acad. Sci.: Washington, DC, 1977.
7. Cheeke, P.R. Rabbit Feeding and Nutrition; Academic
Press: Orlando, FL, 1987.
8. de Blas, C.; Wiseman, J. The Nutrition of the Rabbit; CABI
Publ.: New York, 1998.
Nutrient Requirements: Nonruminant Herbivores 677
Nutrient Requirements: Ruminants
C. L. Ferrell
United States Department of Agriculture, Agricultural Research Service, Clay Center, Nebraska, U.S.A.
INTRODUCTION
Nutrient needs of tissues of ruminants are similar to those
of nonruminants. Tissues of ruminants require oxygen,
water, energy, amino acids, fatty acids, minerals, and fat-
and water-soluble vitamins. Dietary needs of ruminants
are simpler and often cheaper than for nonruminants
because of anaerobic microbial metabolism in the rumen.
Microbial metabolism of dietary intake also increases the
complexity of relating dietary intake to nutrients available
to the animal.
WATER
Water is required by the animal for regulation of body
temperature and acts as a solvent necessary for transport

of nutrients, metabolites, and waste products. The
requirement for water reflects needs for accretion in body
tissues (e.g., growth, pregnancy) and milk production plus
that lost from the animal. Water is lost from the animal by
excretion as urine or feces, from the lungs as water vapor
during respiration, and from skin by evaporation. Losses
vary considerably and depend in part on activity, air
temperature, diet, and water consumption. Because feeds
contain water, and oxidation of nutrients produces water,
not all water needs must be provided by drinking.
ENERGY
Energy is defined as the potential to perform work and is
required to perform the ‘‘work’’ of living. Energy
requirements depend on the additive needs of individual
cells and vary according to physiological needs imposed
upon those cells. Energy is derived from the metabolism
of carbohydrates, proteins or amino acids, and fats and can
be supplied from the diet, or if dietary supply is
inadequate, from body tissues (fat, protein, glycogen).
Carbohydrates are the primary dietary source of energy of
ruminants. Dietary protein, peptides, and amino acids
contribute up to about 20% to the energy supply. Fat is
low (2 4%) in diets typically consumed by ruminants, and
is, thus, not a major contributor to energy supplies. Fat
may be added to diets of feedlot cattle or lactating cows to
increase the energy density of the diet, but dietary fat
contents of greater than 8 10% may have adverse effects
on rumen microbial metabolism.
Cellulose, hemicellulose, and starch are the major
carbohydrates utilized by ruminants. Many species of

bacteria in the rumen produce cellulase enzymes capable
of hydrolyzing the
b 1 4 linkages between the glucose
units in cellulose and others hydrolyze the
b 1 4 linkages
in hemicellulose. Many species of microbes, as well as
a
amylases present in pancreatic secretions of all animals,
hydrolyze
a 1 4 linkages of starch. The symbiotic
relationship between ruminants and rumen microbes
allow utilization of forages and other feeds, especially
those containing complex carbohydrates such as cellulose
that are unusable or poorly utilized by nonruminants.
Volatile fatty acids (VFA; acetate, proprionate, butyrate,
etc.) are primary metabolic end-products of carbohydrate
(and protein) hydrolysis by anaerobic microbes in the
rumen and serve as the major energy source of ruminants.
One of the major metabolic differences between rumi-
nants and nonruminants is the reliance of ruminants on
VFAs as the major substrates for oxidative metabolism
and energy storage.
Little glucose is available for absorption from the
digestive tract of ruminants. However, glucose is required
by nervous tissue, muscle, adipose, mammary gland, and
gravid uterus. Glucose requirements of ruminants are met
through gluconeogenesis, primarily from proprionate,
amino acids (e.g., alanine, glutamine, aspartate, gluta-
mate), glycerol, and lactate. In spite of the lower blood
glucose concentrations and extra metabolic steps required

to provide glucose, requirements of ruminants appear to
be similar to nonruminants.
AMINO ACIDS
It is generally assumed that tissue requirements for amino
acids of ruminants are similar to those of nonruminants.
However, this assumption has not been rigorously tested.
Amino acids are required for synthesis of protein and
other essential compounds and provide the carbon
skeleton for a major proportion of glucose needed by
the ruminant. Lysine, arginine, histidine, isoleucine,
678 Encyclopedia of Animal Science
DOI: 10.1081/E EAS 120019736
Published 2005 by Marcel Dekker, Inc. All rights reserved.
leucine, methionine, phenylalanine, threonine, tryptophan,
and valine must be supplied from the digestive tract, but
specific requirements have not been well defined.
Requirements have been estimated based on rate of
accretion and amino acid composition of whole body
protein.
[1]
Ruminants have the unique ability to subsist and
produce without dietary protein or amino acids due to
synthesis of microbial protein from a wide variety of
nitrogen (N) sources within the rumen. The sources of N
that microbes utilize for protein synthesis include dietary
protein and nonprotein N (NPN), as well as N recycled to
the rumen via saliva or diffusion (primarily as urea). Most
ruminal bacteria can use ammonia N as a source of N, but
much of the N used by bacteria is derived from amino
acids or peptides, if available. Ruminants can grow,

reproduce, and lactate with only NPN as a source of N, but
additional sources of amino acids are required to achieve
maximal productivity. Rumen microbes, as well as dietary
protein that escape (bypass) degradation in the rumen,
supply the intestine with protein for digestion and
absorption as amino acids. Microbial N composes about
40% of the nonammonia N entering the intestine on high-
energy diets with high protein levels, about 60% with low
protein diets, and 100% with purified, NPN-supplemented
diets. Biological values of microbial protein range from
about 65 to 90, with an ideal value of 100.
The quantity and quality of protein reaching the small
intestine is modulated by the effects of degradation and
synthesis in the rumen. Both quality and quantity of
protein available to the animal may be improved by
microbial metabolism if a diet containing a low level or
low quality of protein is fed. Microbial action may
decrease the quantity and quality of available protein
when a diet containing a high level of high-quality protein
is fed. The amino acid profile of microbial protein is
relatively constant and well balanced relative to tissue
needs, and thus is utilized very efficiently. However, die-
tary protein escaping ruminal degradation may be less
well balanced. As with nonruminants, a poorly balanced
supply of amino acids results in increased catabolism
of amino acids. Unless used for synthesis of protein or
other essential compounds, amino acids are catabolized
with the N being converted to urea and the carbon skel-
eton being oxidized or used for storage. A poorly balanced
amino acid supply results in inefficient use of N and is

energetically costly.
MINERALS
At least 17 minerals are required by ruminants. Macro-
minerals (those required in large amounts) include cal-
cium, magnesium, phosphorus, potassium, sodium, chlo-
rine, and sulfur. Required microminerals (those required
in small amounts) are chromium, cobalt, copper, iodine,
iron, manganese, molybdenum, nickel, selenium, and
zinc.
[1–3]
Other minerals including arsenic, boron, lead,
silicon, and vanadium have been shown to be essential
for one or more animal species, but there is no evidence to
indicate these minerals are of practical importance in
ruminant diets. Two features of ruminant nutrient require-
ments are noteworthy. Phytate phosphorus is not well
utilized by nonruminants, but as a result of microbial
fermentation, is utilized readily by ruminants. Cobalt
functions as a component of vitamin B
12
. Ruminants are
not dependent on a dietary source of vitamin B
12
, but
cobalt is required for its synthesis by rumen microbes.
Many of the essential minerals are usually found in typical
feeds, while others must be provided by dietary supple-
mentation for optimal animal performance. Supplementa-
tion in excess of requirements increases mineral excre-
tion. In addition, several essential minerals (e.g., copper

and selenium) are toxic at high levels, while others,
although not toxic per se, interfere with absorption of
other essential minerals when included in the diet in
excessive amounts.
VITAMINS
Ruminants require fat-soluble vitamins (A, D, E, and K)
and water-soluble vitamins (B complex), but typically
only have a dietary requirement for vitamins A and E.
Vitamin A is essential for normal growth and reproduc-
tion, maintenance of epithelial tissues, and bone
development, and is a constituent of the visual pigment
rhodopsin present in the rod cells of the retina. Vitamin
A (retinol) per se does not occur in plants, but its
precursors, carotenes, occur in various forms. Beta-
carotene is the most widely distributed. High-quality
forages provide carotenes in large amounts, but tend to
be seasonal. Carotenes are rapidly destroyed by sunlight
and air. Conversion of carotenes to retinol occurs in
intestinal mucosal cells, but efficiency of conversion
tends to be lower in ruminants than in nonruminants.
Functions of vitamin E include serving as an antioxidant
and in the formation of cellular membranes. Vitamin E
occurs in feedstuffs as a-tocopherol. Vitamin E require-
ments depend on dietary concentrations of antioxidants,
sulfur-containing amino acids, and selenium. Because
vitamin D is synthesized by ruminants exposed to
sunlight, or fed sun-cured forages, these animals rarely
require vitamin D supplementation. Physiological needs
of Vitamin K and the B vitamins (e.g., B
12

, thiamin,
niacin, riboflavin, pyridoxine, pantothenic acid, biotin,
and choline) have been clearly demonstrated, but
Nutrient Requirements: Ruminants 679
requirements are normally easily met by microbial
synthesis in the rumen.
CONCLUSIONS
At the tissue level, nutrient requirements of ruminants are
believed to be similar to those of nonruminants. However,
a symbiotic relationship between the animal and microbes
within the digestive tract (especially in the rumen and
reticulum) results in several unique features of ruminant
dietary requirements. In particular, complex carbohy-
drates, such as cellulose, can be effectively digested and
metabolized by rumen microbes. Volatile fatty acids
(VFA), by-products of microbial fermentation of carbo-
hydrates or protein, provide a major proportion of the
energy available to ruminants. Dietary protein, amino
acids, or nonprotein nitrogen, such as urea, may be
incorporated into microbial protein, which serves as the
primary source of amino acids to ruminants. Alternatively,
amino acids from the diet may escape microbial
fermentation in the rumen and become available for
intestinal absorption. In addition, urea produced within the
animal may be recycled to the digestive tract, thus
providing a source of N for microbial synthesis of amino
acids. Similarly, B vitamins, vitamin K, and essential fatty
acids are normally produced in sufficient quantities by
microbial fermentation to meet animal requirements;
however, microbial synthesis of vitamin B

12
requires a
dietary source of cobalt.
REFERENCES
1. NRC. Nutrient Requirements of Beef Cattle, 6th Revised
Ed.; National Academy Press: Washington, DC, 2000;
Update.
2. NRC. Nutrient Requirements of Sheep, 6th Revised Ed.;
National Academy Press: Washington, DC, 1985.
3. NRC. Nutrient Requirements of Dairy Cattle, 6th Revised
Ed.; National Academy Press: Washington, DC, 1989.
Update.
680 Nutrient Requirements: Ruminants