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Module 2: Nutritional Strategies to Minimize
Nutrient Loss to Manure
By David J. Hansen, University of Delaware
Intended Outcomes
The participants will learn
 Basic concepts of animal nutrition.
 How to improve nutrient yield.
 Techniques for reducing ammonia losses.
 Economic considerations when reducing nitrogen and phosphorus excretion.
Contents
1. Introduction
2. Nutrient Inputs
A. Basic Nutrient Cycling in Animal Systems
B. National Research Council (NRC) Guidelines for Diets
C. Feed Waste
3. Dietary Strategies to Improve Nutrient Efficiency
A. Dairy
B. Beef
C. Swine
D. Poultry
References
Appendix A: NRC Dietary Tables
Questions
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Reviewers
The author wishes to thank Al Sutton, Purdue University, and Bob von Bernuth, Michigan State
University, for their review of this module.
This module was adapted from the Livestock and Poultry Environmental Stewardship
(LPES) curriculum, Lesson 10 authored by Theo van Kempen and Eric van Heugten,
North Carolina State University; Lesson 11 authored by Paul Patterson, The
Pennsylvania State University; Lesson 12 authored by Rick Grant, University of
Nebraska, and Stanley (Lee) Telega, Cornell University; and Lesson 13 authored by Galen
Erickson, University of Nebraska, and Todd Milton, formerly of the University of
Nebraska, courtesy of MidWest Plan Service, Iowa State University, Ames, Iowa, 500113080.
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Introduction
Consumers demand safe, high-quality meat, eggs, and milk at reasonable prices. Increasingly, these
consumers are demanding that livestock and poultry operations producing these goods be operated in
ways that minimize negative impacts to the environment. Of particular concern are nutrients, primarily
nitrogen (N) and phosphorus (P), excreted in manure. The most effective way to reduce the excretion of
N and P is through feed management.
The goal of livestock and poultry feed management is to maximize feed efficiency by providing
biologically available nutrients in quantities sufficient to ensure productivity while minimizing nutrients
excreted in manure and urine. Although both animals and birds are relatively inefficient in their
“conversion” of N and P from feed, commonly passing more than 50% of N and P through to feces,
research indicates that dramatic improvements are possible. However, the various species have very
different sets of challenges. For example, non-ruminants such as swine and poultry have a difficult time
digesting phytate-P and require inorganic P supplements or the addition of phytase to increase availability
of P for animal growth.
This module will focus on nutritional strategies for maximizing nutrient utilization by animals, which
reduces nutrient excretion and increases profitability.
Nutrient Inputs
Basic Nutrient Cycling in Animal Systems
All animal diets have the same basic goal: to provide available nutrients in adequate amounts and
proportions to meet the maintenance and production requirements of the animals while avoiding waste
and overfeeding. Providing nutrients in excess of animal requirements results in increased costs of
production and contributes to potential environmental problems.
Inefficiencies can be caused by a variety of factors including housing conditions (temperature,
moisture, etc.), management (cleanliness, proper maintenance of equipment), genetics, and feed quality
(Figure 2-1). Therefore, efforts to maximize efficiency and minimize the loss of nutrients from this
system can be targeted at many different points. While it may not be practical to address all these points
simultaneously, the following discussions should help producers identify those areas where improvements
are most likely to work in their operations.
National Research Council (NRC) Guidelines for Diets
In 1916, the National Academy of Sciences organized the NRC to “…associate the broad community
of science and technology with the Academy's purposes of furthering knowledge and advising the federal
government.” The NRC has, in turn, organized subcommittees to address animal nutrition issues. These
subcommittees have developed guidelines for beef cattle (Nutrient Requirements of Beef Cattle: 7th
Revised Edition 2000), dairy (Nutrient Requirements of Dairy Cattle: 7th Revised Edition 2001), poultry
(Nutrient Requirements of Poultry: 9th Revised Edition 1994), and swine (Nutrient Requirements of
Swine: 10th Revised Edition 1998). These guidelines are based on many years of trials under both
controlled and field conditions and represent the “state of the art” in animal nutrition. Additional
information is included in Appendix A.
Feed Waste
Although not strictly a dietary issue, feed waste is an important loss of nutrients that can occur before
they can be ingested by the animals. Poor feeder design, poor feeder management, and spoilage during
storage can lead to losses as high as 20% for both animals and birds. Little research has been performed
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Feed provided
Waste
Feed waste
Feed consumed
Inefficiencies
Intestinal secretions
(enzymes, cells)
Undigested
feed
and secretions
Nutrients absorbed
Maintenance
Nutrients available for
growth
Mismatch
Nutrients used for
growth
Inefficiencies
Growth
Figure 2-1. Nutrient paths in animal feeding operations.
Source: van Heugten and van Kempen 2000
to evaluate the effect of feed wastage on environmental pollution. However, its economic impact on
producers can be substantial.
For example, swine feed waste is strongly influenced by the presentation of the feed. Mash feed
tends to cling to the animal’s chin and nose, ultimately leading to waste. Gonyou and Lou, (1998)
determined that each time an animal leaves a feeder it takes 1.5 grams of feed with it. Given that swine
typically access the feeder 60 times per day, this theoretically could amount to wasting 90 grams (0.2 lb)
of feed. Swine also tend to root through the feed, which leads to the waste of 3.4% of the feed in poorlydesigned feeders (Gonyou and Lou 1998). Pelleting feeds may reduce both forms of feed waste by as
much as 5% (Vanschoubroeck et al. 1971). Feed costs commonly account for 60% to 70% of the cost of
raising poultry. Feed waste for poultry is strongly influenced by feeder maintenance and positioning.
Critical issues include proper positioning of feedings or feeding troughs (height appropriate to bird size),
consistent “flow” of feed, and depth of feed in the feeders. Too much feed in feeders can lead to
increased spillage and waste.
To minimize feed waste,
 Install feeders/feed systems that are designed to minimize feed waste.
 Adjust and clean feeders frequently.
 Use pelleted feeds.
Dietary Strategies to Improve Nutrient Efficiency
Improvements in nutrient yield can come from a number of different sources ranging from changes in
rations such as the use of low-phytate corn to diet supplements such as growth hormones, enzymes, or
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amino acids (AAs). The following section will discuss strategies by animal type: dairy, beef cattle, swine,
and poultry.
Dairy
Nutrients normally become concentrated on
dairy farms because more nutrients are brought into
the farm system than leave in the products sold
(Klausner 1993). Although actual values vary from
farm to farm, the percentages of N and P remaining
on the operation range from 59% to as high as 81%
(Table 2-1). Since the magnitude of nutrient loss
to the environment is proportional to the difference
between inputs and outputs, it is important that
managers have nutrient management plans that
ensure efficient nutrient use and minimize the environmental impact of their operation.
The primary objective of any dairy feeding program is to achieve profitable milk production. For
many producers, this means high levels of milk production. It is possible for high milk production to
coexist with reduced excretion of manure nutrients. Keep in mind, however, that the percentage of
nutrients needed for maintenance decreases as milk production increases.
N
The following strategies provide ways to control N excretion:
 Increase dry matter (DM) intake.
 Improve forage quality
 Consider forage protein fraction.
 Consider feeding method.
 Consider supplemental protein source.
 Monitor blood urea nitrogen (BUN) and milk urea nitrogen (MUN).
Increase DM intake. The percentage of crude protein (CP) required in the ration to provide an
absolute amount of protein to support milk production varies with intake level. A 5% increase in intake
reduces the CP needed by about 1%. So, more CP could come from high-quality homegrown feeds,
decreasing the amount of purchased feed required. Also, increasing intake level increases microbial
protein synthesis in the rumen, which decreases the need for higher dietary protein.
Improve forage quality. High-quality legume/grass forage contains more protein, less fiber, and
more energy, so it can provide more protein and digestible DM to the ration, reducing reliance on
purchased protein sources. If purchased N inputs are minimized, the degree of N introduced into the
environment from sources outside the farm will be reduced. In general, providing energy from highly
digestible, high-quality forages will maximize dairy cow performance and health.
Consider forage protein fractions. Supplement highly degradable forage protein (such as
legume silage) with less degradable sources of protein (such as corn silage). Often, this will result in
improved milk production at lower CP levels in the diet. Common and effective supplemental sources of
rumen undegradable protein (RUP) include blood meal and feather meal combinations, distillers grains,
treated or heated soybeans and other oilseeds, and fish meal.
Consider feeding method. Method of feeding can alter N utilization. Feeding sequence, feeding
frequency, and grouping strategy all influence how the cow uses dietary N. Synchronizing the delivery of
readily available, or “rumen degradable” protein (RDP) and rumen fermentable carbohydrate can increase
the cow’s efficient use of N and decrease N excretion (NRC 2001). Synchronizing the digestion of
proteins and carbohydrates results in greater microbial protein production. Grouping is especially
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Table 2-1. Mass N and P balances for New York dairy farms.
Size of Dairy, Number of Cows*
45
320
500
-----(tons of N per year)-----
Input
Purchased fertilizer
1.0
13.5
26.1
Purchased feed
3.8
43.8
78.5
N fixation by legumes
1.3
14.6
13.9
0
0.1
0
6.1
72.0
118.5
Milk
2.0
18.6
26.4
Cattle sold
0.1
1.9
1.9
Crops sold
.01
0
0
Total Outputs
2.2
20.5
28.3
Remainder
3.9
51.5
90.2
64%
71%
76%
Purchased cattle
Total inputs
Output
% Remaining on farm
-----(tons of P per year)-----
Input
Purchased fertilizer
1.2
2.0
5.5
Purchased feed
1.0
8.4
14.2
Purchased cattle
0
0.03
0
2.2
10.4
24.2
Milk
0.36
3.8
5.5
Cattle sold
0.05
0.5
0.5
Crops sold
0.01
0
0
Total Outputs
0.43
4.3
6.0
Remainder
1.8
6.2
18.2
81%
59%
75%
Total inputs
Output
% Remaining on farm
*Assumes annual milk production of 16,000; 23,700; and 22,000 gal, respectively.
Source: Klausner 1993
important to avoid over-supplementing N and other nutrients. A one-group total mixed ration may be
easier to manage, but a multiple grouping approach minimizes protein overfeeding, decreases N
excretion, and lowers feed costs.
Work by Van Horn (1992) illustrates the N excretion from two different diet formulation approaches.
One diet was high in RDP and the other diet was lower in RDP, while meeting the overall protein
requirement of the cow with higher levels of RUP, or “bypass” protein. High-producing dairy cows
require a proper balance of RUP and RDP to meet their requirements for metabolizable protein (MP).
Metabolizable protein is the protein that the cow actually absorbs and uses for production (NRC 2001).
The requirement for RUP for lactating dairy cows is 35% to 38% of total CP. When cows were precisely
fed to meet RUP and RDP requirements, they excreted 223 pounds of N per year. When cows were fed
simply to meet their total CP requirement, however, they excreted 260 pounds of N per year.
Consider supplemental protein source. Use protein supplements to allow the cow’s RDP and
RUP requirements to be met without overfeeding CP. In the future, more emphasis will be placed on the
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AA content of various protein sources. Ultimately, an imbalance of AAs available to the cow for
digestion and metabolism will impair milk and milk protein production.
Monitor BUN and MUN. Blood urea nitrogen and MUN analyses can be used as a signal, or “red
flag,” to point out potential problems in your feeding program. A BUN level in excess of 18 to 20 mg/dl
or a MUN level in excess of 18 mg/dl can be associated with lower reproductive performance, higher feed
costs, health problems, and poor milk production. High MUN values also reflect excessive dietary CP or
low rumen degradable nonfiber carbohydrates (NFC). The NFC fraction, usually composed of starch and
other sugars, can be low when insufficient grain is fed or grain is improperly processed.
James et al. (1999) fed dairy heifers (570-1,080 lb) total mixed rations containing either 9.6% or
11.0% CP. This 14% reduction in N intake resulted in a decrease of 29.6%, 19.8%, and 7.4% or urea-N,
total N, and percentage N excreted in manure, respectively. In an in-vitro experiment, ammonia
volatilization was reduced by 28.1%.
P
Phosphorus is the most expensive nutrient in typical mineral-vitamin formulations for dairy cattle.
Phosphorus is often supplemented by adding monocalcium or dicalcium phosphate, monosodium
phosphate, or ammonium phosphate (high availability); steamed bone meal, defluorinated phosphate, or
sodium tripolyphosphate (medium availability); or low-fluorine rock phosphate or soft rock phosphate
(low availability) to feed mixes. Most commercial premixes include additional P.
Since the 1960s, several researchers have examined P metabolism in the lactating dairy cow. Current
guidelines (NRC 2001) specify ranges of 0.32% to 0.42% P during milking and lactation. Although it is a
common practice to feed 0.50% to 0.60% P in some parts of the United States, many controlled studies
indicate no benefit of these high levels.
Recent research from the U.S. Dairy Forage Research Center in Madison, Wisconsin (Satter and Wu
1999, Wu et al. 1998) confirms that high-producing dairy cows require approximately 0.40% P in the
dietary DM for optimal milk production and reproductive performance. Feeding higher than
recommended levels of dietary P has not improved either milk production or reproductive efficiency in
controlled research studies.
Feeding adequate P is important for cow performance and health, but 0.40% to 0.45% of the dietary
DM is near the optimal dietary content for lactating dairy cows. For a cow producing 100 lbs to 120 lbs of
milk daily, a diet containing 0.45% P meets the NRC (1989) recommendation. However, the same dietary
P level provides about 140% of the daily P requirements for a cow producing only 40 to 50 lbs of milk.
Based on this information, it is important that the milking herd is grouped by production level and that
multiple rations are formulated over the complete lactation cycle to minimize P excretion into the
environment.
Economics of reducing N and P excretion
Dairy producers have considerable control over mineral excretion in the manure by manipulating the
amount of mineral in the feed. For example, feeding a ration containing 0.45% P versus a diet containing
0.55% P would save about $0.05/cow daily. For 100 cows over a year’s time, it would save about $1,825.
In a study reported by Klausner et al. (1998), precision feeding decreased N excretion by 34% while
improving milk production. Milk production increased 13%, and economic returns improved by more
than $40,000 per year for a 320-cow dairy herd. Similar results were reported in other studies (Rotz et al.
1999, Tylutki and Fox 2000).
Recent surveys conducted in the United States indicate that producers typically formulate dairy diets
to contain 0.45% to 0.50% P (dry basis). This amount is approximately 20% to 25% in excess of the NRC
suggested requirement (NRC 2001), and the excess P supplementation costs $10 to $15 per cow annually.
A 20% decrease of dietary P can be achieved without decreasing animal performance, and this decrease
will result in a 25% to 30% decrease in the P content of manure and a similar decrease in the amount of
land required for manure application. As regulations evolve toward restrictions on land application of
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manure based on P content, these improvements have obvious implications for the viability of the animal
operation.
Beef Cattle
As is the case with dairy (and all other animal operations), nutrients become concentrated because
more are brought into the farm system than leave in the products sold. Studies in Nebraska (Bierman et
al. 1999; Erickson et al. 2000, Erickson and Klopfenstein
2001) have shown that N and P excretion are highly
correlated to the amount of N and P intake. For example,
increasing the amount of CP from 12% to 13.5% increased
the amount of N excreted by 13.5 pounds per steer in
yearling steers over 150 days and 9 pounds per steer in
calf-fed steers over 200 days.
Diet formulation obviously has a large impact on
nutrient excretion. However, it is important to note that
simply decreasing the amount of CP in the diet is
impractical; there are certain minimum protein
requirements that must be met to ensure optimal
performance. The following describes dietary strategies for reducing N and P excretion in beef cattle.
N
Beef cattle finishing diets are commonly formulated on the basis of providing a minimal amount of
CP; usually at least 12.5%. These diets consider all protein equal in value; even urea is considered equal
in value to other natural protein sources. However, during the past 15 to 20 years, research has
consistently found that all protein sources are not nutritionally equal in beef cattle diets. This work
suggests that it is important to consider protein availability when formulating diets.
The MP system. In 1996, the NRC published an MP system for beef cattle. Metabolizable protein
is defined as the total amount of protein absorbed from the animal’s small intestine for metabolic
purposes in the animal. The MP system describes animal requirements and differentiates feedstuffs into
two categories: degraded intake protein (DIP) and undegraded intake protein (UIP). The DIP portion
refers to the requirements of the ruminal microorganisms. The MP system attempts to control the balance
of DIP and UIP from feed grains and supplemental protein sources to ensure that microbial N
requirements and host animal requirements are met.
For example, corn grain contains about 8.5% CP. Of that CP, 60% is considered UIP and 40% is
considered DIP. Therefore, dry-rolled, corn-based finishing diets typically need sources of supplemental
protein that are degradable (DIP). The microbial protein that is produced from the digestion of corn grain
in combination with the high UIP fraction of corn protein will meet the animal’s MP needs. Conversely,
high-moisture ensiled corn is 8.5% CP, but only 40% of the CP is UIP and 60% is DIP. Therefore, when
high levels of high-moisture corn are used in finishing diets, especially for young calves, a supplemental
source of UIP may be needed in combination with the supplemental DIP to ensure that the animal’s MP
requirements for maximal growth are met.
Table 2-2 shows a comparison of a control diet (formulated on a CP basis) and an experimental diet
based on the MP system. (The control diet for calves was formulated as 13.5% CP throughout the
feeding period.) Calves on the experimental diet consumed about 9 pounds less protein. Without
compromising animal performance, the researchers in that study lowered the CP fed by 1.5% to 2% of
diet DM and reduced N excretion by 15% to 20%.
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Table 2-2. Performance and N balance of yearling and calf-fed steers fed a typical feedlot finishing diet (control) or
a finishing diet adjusted to match the animal’s protein requirement with time (phase).
Yearlings (May to Oct)
Calves (Nov to May)
Control
Experimental
Control
Experimental
Daily gain, lbs
3.98
4.07
3.45
3.40
Feed efficiency
6.33
6.02
5.88
6.10
Intake, lbs
72.82
59.39
81.4
72.23
Retentiona, lbs
7.90
7.92
10.14
10.04
Excretionb, lbs
64.92
51.47
71.26
62.18
Manure, lbs
12.91
19.61
43.51
41.53
Soilc, lbs
3.85
-0.89
-3.66
-6.46
Runoffd, lbs
2.12
1.51
2.10
2.21
Volatized, lbs
46.04
31.25
29.31
24.91
% Volatized
70.9
60.7
41.1
41.10
Feedlot Performance
N
a
N retention based on daily gain, RC (1996) equation for retained energy and retained protein
N excretion calculated as intake minus retention
c Soil is core balance on pen surface before and after trial; negative values suggest removal of nutrient present before trial
d Volatized calculated as excretion minus manure soil minus runoff. Source: Erickson et al. 1999
Source: Erickson and Klopfenstein 2001
b
When finishing younger animals, like calf-fed steers (550-lb starting weight), the type of
supplemental protein needed to meet the MP requirement changes significantly during the feeding cycle.
The total MP requirement does not necessarily change with time, but the ratio of DIP and UIP needed in
the diet does. As time on feed increases for the calf-fed animal, feed intake increases, more feed protein is
consumed, and a larger supply of UIP is provided to the animal. In addition, as the animal approaches
finished weight, the composition of gain changes from less muscle to more fat deposition, reducing the
amount of MP needed for muscle growth. Although the amount of muscle growth decreases, the need for
MP for maintenance increases as the animal becomes larger. With these biological changes of the animal
and increased UIP supply from the basal ration, supplemental UIP can be reduced, and consequently, the
total amount of supplemental protein fed can be reduced as the animal approaches finished weight.
Protein supplementation for feedlot cattle is a dynamic and complex issue. When formulating diets to
reduce N excretion in feedlot cattle, consider the following issues:
 Type of animal being fed (calf-fed steer vs. yearling steer)
 How much and what type (DIP or UIP) of protein the basal dietary ingredients provide
 What type of supplemental protein source (DIP or UIP) is needed to complement basal
ingredients, meeting the animal’s needs
Ammonia losses most commonly occur as urea from urine is converted into ammonium following
excretion. Therefore, dietary strategies that reduce urinary N also reduce ammonia losses. Satter et al.
(2002) noted that employing phase feeding can reduce N excretion by 12% to 21%, and these reductions
result in decreased ammonia losses of 15% to 33%.
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P
Phosphorus is both expensive to supplement and may have some of the most deleterious effects on
the environment. This is important because recent research has shown that supplemental P in feedlot
finishing diets is usually unnecessary. For example, Erickson et al. (1999) found no growth response for
yearling steers (850 lbs) fed diets in which the P concentration ranged from 0.14% to 0.34% of the diet
DM (Table 2-3). Similar results were obtained from a study conducted on finishing calves (580 pounds)
fed for 204 days (Erickson et al. 2001). Since corn grain contains about 0.32 ± 0.04% P (NRC 1996) on a
DM basis, the contribution of P from corn grain alone is adequate for feedlot cattle.
Table 2-3. Effect of dietary P level on finishing steer performance and bone ash concentration for yearlings.
Dietary P level, % of DM
Calves
Item
0.14
0.19
0.24
0.29
0.34
P intake, g/d
16.4
19.9
27.6
32.0
36.2
DM intake:
lbs/day
24.3
22.7
25.4
24.5
23.8
Daily gain:
lbs/day
3.88
3.57
3.79
3.85
3.37
6.49
6.36
6.71
6.32
7.04
Grams (first phalanx)
28.3
27.5
28.9
27.5
28.5
Grams/100kg of BW
8.01
8.02
8.20
7.83
8.46
Performance
Gain/feed
Bone ash
Source: Erickson et al. 1999.
Phytate-P is readily available to ruminants such as feedlot cattle. On average, 95% or more of the P
bound to phytate is released during ruminal fermentation for the animal’s subsequent use (Morse et al.
1992). Based on current data, supplementation of inorganic P is not necessary to compensate for phytates
in feed grains or other feedstuffs for feedlot cattle.
There are several approaches that reduce the excretion of N and P from feedlot cattle. A brief
discussion of some of these methods is provided below.
Test feedstuffs from your operation. One of the most important steps in reducing excess N and
P excretion from any operation is to determine as precisely as possible their level in the diet so that diets
can be formulated correctly and adjusted to reduce excesses.
Supplement the diet with the correct source of protein. Based on ingredient analyses,
balance your diet so that the basal feed ingredients, supplemental protein, and P complement each other to
meet animal requirements.
Discontinue use of supplemental P in feedlot diets. When grain is the major feed ingredient
in the diet, current research indicates that supplemental P is not needed.
Consider a phase-feeding program. This is especially true in finishing younger animals, where
the protein requirement changes considerably over time. The phase-feeding approach of supplementing
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protein means using more than one finishing diet in the feedyard. Yearling steers are less of an issue
since the change in N and P requirements during the feeding period remains relatively similar.
Take advantage of the type of protein in the feedstuffs. Utilizing differences in the DIP and
UIP of feedstuffs to complement each other in the diet can reduce the need for supplemental protein. A
good example is feeding combinations of high-moisture and dry-rolled corn based on the desired level of
UIP in the diet. Additionally, many byproducts can deliver a considerable amount of DIP and/or UIP to
the diet. If not properly taken into consideration, these additions can result in elevated P levels in
excreted manure.
Evaluate your rations with available tools. Evaluate your feedlot rations with regard to the
need for supplemental DIP and UIP with such tools as the NRC (1996) model. You can download this
software from the following website: <http://www.nap.edu/readingroom/books/beef model/>.
Swine
Diet formulation issues in swine (and poultry) are complicated
by the nature of the industry; often, individual producers do not have
the resources (or the authorization) to make adjustments to feeding
regimens. Even independent swine producers purchasing feed
“packages” find that these diets are most often based on CP and
formulated to meet nutritional requirements at a minimum dietary
cost. It may be desirable for producers to consider the potential
economic and environmental benefits of a diet that can dramatically
reduce excretion, particularly in situations where nutrient disposal is
costly or there is limited land for manure application.
N
Swine diets typically contain higher protein contents than the minimum required because most feeds
contain only two major AA sources (corn and soybean meal). Because diets are usually formulated to
supply at least five AAs at a certain minimum level for optimal performance (Table 2-4), a diet that uses
two sources has little flexibility and the result is that some AAs are provided in excess to ensure adequate
amounts of the other AAs.
Table 2-4. True ileal AA profiles for maintenance and growth expressed relative to lysine.
Maintenance
Growth
AA
Expressed as % of Lysine AA
Lysine
100
100
Threonine
151
60
Tryptophan
26
18
Methionine
28
27
Sulfur AAs
123
55
Valine
67
68
Leucine
70
102
Isoleucine
75
54
Histidine
32
32
Phenylalanine
50
60
Phenylalanine + Tyrosine
121
93
Arginine
-200
48
Source: NRC 1998
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For example, work by Lenis and Schutte (1990) suggested that the protein content of a typical swine
ration could be reduced three percentage points (e.g., from 16% to 13%) by replacing soybean meal
(SBM) with synthetic AAs and corn without negative effects on animal performance. Even a less
comprehensive approach, such as simply replacing some of a corn and soybean meal (CSM) diet with
synthetic lysine, has been shown to reduce dietary protein by 1.5% (Reese and Koelsch 1999). Such
reductions could exert a large impact on N excretion in manure. Schutte et al. (1993) and Monge et al.
(1998) both found that for each percentage point that N is reduced in the feed, N excretion is reduced by
10% to 11%. Van der Peet-Schwering et al. (1997) found that reducing protein by 1% decreased
ammonia losses by 10% to 11%.
Split-sex and phase feeding. An animal’s nutrient requirement changes with age, sex, and
growth potential. If the objective is to avoid wasting precious nutrients, then it becomes important to feed
diets that are formulated to match the animal’s nutrient requirement. Examples of this are split-sex
feeding and phase feeding. For split-sex feeding, differences in nutrient requirements among gilts,
barrows, and possibly boars are taken into consideration. Barrows typically have a higher feed intake
capacity without a larger potential for lean gain, and thus diets should be fed with somewhat less protein.
Gilts require a higher protein diet for lean tissue gain.
Phase feeding refers to feeding programs that match the animal’s nutrient requirement as it changes
with the animal’s age and size. To minimize nutrient waste, the animal’s diet is changed continuously to
match its requirements. Changing from a one-phase feeding program between 50 pounds and 250 pounds
to a two-phase feeding program should reduce N excretion by 13%, while going to a three-phase feeding
program may reduce N excretion by 17.5%.
Den Brok et al. (1997) showed that using benzoic acid improved feed conversion from 2.92 to 2.83
while reducing ammonia emissions by 40%. This improvement occurs primarily through decreasing the
pH of the urine and/or manure. Similar results have been obtained, under experimental conditions, with
use of calcium sulfate in swine diets (Mroz et. al 1996).
From a practical perspective, it is not feasible to change the feed often, e.g., weekly, unless feeding
equipment is available that is designed for this purpose. However, work by Koehler (1998) shows the
economic benefits of phase-feeding grower-finish pigs (Table 2-5).
Table 2-5. Savings in feed costs with phase feeding for grow-finish pigs.
Savings over TwoNumber of Phases
Diet Cost/Pig
Phase Program
Increase in Savings per
Additional Phase
-----------------------$----------------------2
42.44
-
-
3
41.41
1.14
1.14
4
41.01
1.54
0.40
5
40.67
1.88
0.34
6
40.43
2.12
0.24
9
40.10
2.45
0.11
12
39.90
2.65
0.6
066
Source: Kohler 1998
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P
Phosphorus is typically overfed to swine. Spears (1996) analyzed commercial feed samples and found
that, on average, P was overfed 40% to 50% (depending on the production phase). Because many states
are beginning to limit land application rates of manure based on P, livestock producers should closely
monitor the P intake of their pigs.
Phosphorus can be fed to maximize bone strength or to maximize performance. The maxima for each
of these parameters is approximately 0.1% dietary P different, with maximum bone strength requiring
more P. Especially for pigs targeted for slaughter, it may not be necessary to optimize the dietary P
content for bone strength, which would lead to a large reduction in P excretion. Care, however, should be
taken to avoid jeopardizing the welfare of the animals.
Phosphorus in commonly used feed ingredients such as corn, wheat, and SBM is predominantly
present in the form of phytate. Phytate is a molecule containing P, but pigs (and poultry) are unable to
use this P because they cannot break down the phytate molecule. In corn, 80% of the P is present as
phytate, while in SBM, 68% of the P is present as phytate. Since this phytate complex is digested poorly
in swine, most of the P contained in the feedstuffs will end up in the manure. To meet the animal’s P
requirement, inorganic P such as dicalcium phosphate is traditionally added to the diet.
Phytase offers an important opportunity to reduce P excretion. Phytase is an enzyme that breaks
down most of the phytate complex, releasing the P in it as well as other nutrients (such as zinc and AAs)
bound by it. Mroz et al. (1994) showed that phytase improves P digestibility in a typical swine diet from
30% to 50%. Under production conditions, van der Peet-Schwering (1993) demonstrated that the use of
phytase resulted in a reduction in P excretion of 32% in nursery pigs.
Feeding low-phytate grains offers another opportunity to reduce P excretion. Although the total
amount of P is the same, low-phytate corn has a P utilization of 75% versus standard corn at about 20%.
Use of low-phytate corn in conjunction with additional phytase enzyme can reduce or eliminate the need
for supplemental inorganic P in diets.
Economics of reducing N and P excretion. The impact of the above strategies depends on the
extent to which they are adopted by livestock producers, which itself depends on the disposal costs of
waste, and thus, the incentive for livestock producers to reduce waste. Adding phytase to a diet at 500
units/kg costs approximately $2.20 per ton of feed for a mash diet. The increase in feed cost required to
reduce P excretion in the range proposed is expected to be less than 1%.
For N, a reduction on the order of 15% to 30% is believed achievable. This reduction is possible in
part through minimizing excesses in diet and through better quality controls at the feed mill. These
measures are not expected to affect production costs since savings in feed costs will offset increased
administrative and feed-handling costs.
A major reduction in N excretion may be achieved by reducing the dietary protein content while
maintaining the feed’s nutritional value, which can be achieved by using a broader variety of feedstuffs,
including synthetic AAs. Because these feedstuffs and AAs are typically more expensive than corn and
soybean, it can be expected that this change will increase the cost of the feed. This increase in feed costs,
however, is expected to be less than 5% for the reduction in N excretion indicated above (a larger
decrease in N excretion is achievable but only at a very high cost). An associated benefit of reducing
dietary protein is that it will reduce odor and may reduce ammonia emissions as much as 10%.
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Poultry
Nutrient excretion from poultry may be
reduced by simple measures such as adding
dietary enzymes, cutting dietary protein, or
reducing additions of inorganic P. However,
the requirements and relationships of
nutrients with feed ingredients are complex;
dietary protein, certain AAs, P, and trace
minerals are essential nutrients for poultry
and must be provided in the bird’s diet.
Failure to provide adequate levels of these
nutrients would be physiologically and
economically unacceptable. The following
discussion is focused on opportunities to
more precisely meet the bird’s requirements
depending on current dietary levels and any
margin of safety additions.
N
Strategies to reduce N excretion can take the form of additives such as enzymes or AAs, formulations
for different development stages, or avoiding compounds that reduce nutrient availability to the birds. As
much as 18% of N in poultry feed can be lost as ammonia, and these losses can be reduced substantially
by the techniques listed below.
Formulate based on AA requirement. Dietary formulation based on bird AA requirements
rather than CP can minimize N excretion by simply reducing total dietary N intake. For example,
Ferguson et al. (1998) demonstrated with broilers that litter N could be reduced more than 16% when
dietary CP was reduced by 2% while maintaining similar levels of dietary AAs. Keshavarz and Jackson
(1992) showed that substitutions of methionine, lysine, tryptophan, and isoleucine for as much as 4% CP
in hen diets significantly reduced protein intake while maintaining egg production and egg weight.
However, attempts to reduce CP in broiler diets have had limited success. At some reduced level of
CP, the bird’s performance suffers even though all the requirements for essential AAs have been
theoretically met. Although it is possible to reduce dietary CP levels by 3% to 4% (13%-22% N) for
broilers and layers, there are biological limits to the amount of dietary protein that can be replaced with
synthetic AAs. Similar limitations with turkeys suggest that we do not fully understand the AA
requirements of these birds; therefore, CP is critical to realize full performance.
Optimize the dietary AA profile. The closer the AA composition of the diet matches bird
requirements for maintenance, growth, and production of meat and eggs, the fewer AAs (N) excreted in
the feces. In CSM-based broiler diets, the most critical AAs are methionine and lysine. Dietary
supplementation of these two AAs can be used to reduce the diet’s CP content and thereby N excretion
until the requirement for the next limiting AA is reached. However, this method leaves many AAs in
excess of their requirement with the excess excreted as fecal N.
Another approach is to deliver an “ideal protein” where the protein portion of the diet meets bird
requirements for each AA with no excesses or deficiencies. With the ideal protein concept, N excretion
would be reduced to a minimum level. Han et al. (1992) published work on the dietary concentrations of
AAs in an ideal protein approach for broiler chickens; the levels of AAs were based on the ratio of
digestible lysine to the requirement for other individual AAs.
Phase feed poultry. Phase feeding is another technique that can reduce manure N and feed cost.
Commercial phase-feeding programs may include as many as six phases to step down dietary protein,
AAs, and other nutrients for broilers starting from 22% CP at hatching to 16% CP when the birds reach 4
pounds in less than 6 weeks (Leeson and Summers 1997). This technique of breaking the requirements of
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growing and adult birds into phases of greater or lesser need for protein and AAs can be further refined to
include more dietary phases when birds are consuming large amounts of feed and N near market weight.
Utilize the “true AA digestibility” of feed ingredients. Work published by universities and
AA manufacturers gives the true digestible AA concentration and/or coefficients of AA digestibility of
cereal grains, plant proteins, and animal proteins. Formulating poultry diets based on the true AA
digestibility rather than on the total AA concentration goes a long way in refining AA levels provided in
the diet.
Because true AA digestibility coefficients are directly related to N retention and inversely related to N
excretion per g of AA, the ecological value of fish meal (threonine or methionine+cystine) is more than
six times greater than that of the low-quality meat and bone meal (Esteve-Garcia et al. 1993). In addition,
it allows a better definition of the AA content of feed ingredients, permitting a closer match with the
birds' requirement. Formulation based on digestible AAs improves daily gain and feed conversion of
growing birds (Esteve-Garcia et al. 1993), and work by the NRC (1994) suggests that calculated
digestible AA requirements are 8% to 10% lower than the requirements for total AAs.
Select feed ingredients with low nutrient variability. Variability of ingredient nutrients can
be a significant problem and induce nutritionists to apply a margin of safety to meet nutritional
requirements. The variability can be a challenge with by-product meals such as meat meal and bakery
byproducts.
Rapid ingredient analysis techniques at the feed mill such as near infrared reflectance (NIR) provide
nutritionists with real-time nutrient concentration and variability to minimize overformulation and
margins of safety. Near infrared reflectance technology for quick determination of protein, fat, and fiber
exists and has been in place in some commercial mills for several years. Digestible AA predictions from
NIR analysis have been developed (van Kempen and Simmins 1997) but are not widely used.
Utilize enzymes and feed additives. Dietary enzymes have the ability to free up the
carbohydrate and fiber portions of many cereals and by-product ingredients for poultry. Water-soluble,
nonstarch polysaccharides (NSP) including arabinoxylans are the major fiber constituents in wheat and
rye that give rise to highly viscous intestinal digesta. Their gel-like viscosity impedes the digestion and
absorption of proteins, fats, and carbohydrates. Inclusion of dietary enzymes (xylanase, arabinoxylanase)
can greatly improve their nutrient utilization.
Another NSP present in barley, oats, and wheat are the beta-glucans. They also reduce nutrient
utilization by way of greater digesta viscosity and are characterized by sticky feces and poor litter
conditions among birds fed significant levels of these cereals. Dietary enzymes tailored for these
ingredients contain ß-glucanase. Soybean and rapeseed meal, peas, beans, and sunflower seeds are
commonly added to poultry diets for their protein and energy value. However, even more complex NSP
are an integral part of the cell wall of these oilseeds and legumes. These NSP increase the viscosity of the
digesta and interfere with nutrient digestion and absorption. The amount of protein in cell walls may
account for 10% to 30% of the total dietary fiber mass. Enzymatic release of these proteins through
selective enzymatic additions can increase AA availability as well.
Phytate P found in most plant materials is a bound form of P that is not well utilized by monogastrics,
especially young birds. Sebastian et al. (1997) studied the apparent digestibility of protein and AAs in
broiler chickens fed a CSM diet supplemented with phytase, a microbial enzyme. Phytase
supplementation increased growth performance in males and females and both apparent ileal and fecal
digestibility of most AAs, particularly in females. Other work with both broilers (Namkung and Leeson
1999, Ravindran et al. 1999) and turkeys (Yi et al. 1996) demonstrated significant improvements in the
digestibility of AAs and protein and apparent metabolizable energy when phytase was added to the diet.
While antibiotic use has gradually decreased, other growth-promoting agents are still used. The mode
of action of most growth-promoting agents is comparable to antibiotics in terms of beneficial
modification of the gut microflora. Eliminating deleterious microorganisms can reduce thickening and
keratinization at the level of the intestinal mucosa (site of absorption), thereby improving nutrient
utilization and feed conversion and reducing nutrients in the waste.
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Probiotics imply the use of live microorganisms that are either viable microbial cultures or their
fermentation products. Most products are centered on Lactobacilli, Bacillus subtillis, and some
Streptococcus species. In most instances, feeding live cultures of “good bacteria” modify the gut
microflora of birds at the expense of coliforms such as E. coli and Salmonella species. The beneficial
effects on nutrient utilization and feed conversion are then similar to antibiotics. With the advent of
genetic engineering, these bacteria can be modified to carry other desirable gene characteristics including
the production of digestive enzymes or antimicrobial substances to aid nutrient utilization and waste
reduction.
Avoid or control ingredient anti-nutritional factors. Anti-nutritional compounds including
trypsin inhibitor in soybeans, lectin in legumes, tannins in sorghum, and the previously mentioned NSP
and phytate P can negatively affect the digestion and use of AAs and other nutrients. These inhibitors are
present in many legumes and cereals.
Soybeans contain a number of anti-nutritional factors for poultry, the most problematic being trypsin
inhibitor. Trypsin is a pancreatic enzyme that aids in the digestion of proteins. Fortunately, the heat
treatment used during SBM processing or soybean roasting is usually adequate to destroy it.
Lectins are proteins in legume seeds that have a high affinity for certain sugar molecules. They can
disrupt the brush borders of cells lining the duodenum and jejunum, causing various adverse effects
including reduced growth, diarrhea, and decreased nutrient absorption. While lectins in soybeans are
relatively nontoxic with little negative activity, field beans (Phaseolus) including kidney beans are highly
toxic in terms of reduced animal performance without moist heat destruction (Cheeke 1998).
Various strains of sorghum are well known for their high tannin content, which can decrease the
protein’s digestion and utilization, leading to increased excretion in the feces (Cheeke 1998).
Specifically, condensed tannins in sorghum react with dietary protein, forming indigestible complexes
that bind with digestive enzymes and reducing the digestibility of all dietary nutrients.
P
Meet bird P requirements. The NRC (1994) recommends 250 mg of available non-phytate P
(nPP) per hen per day, while Leghorn breeder guides advise producers to provide 450 to 460 mg per hen
per day early in lay and 288 to 390 mg late in the hen’s cycle. Boling et al. (2000) reported that 0.15%
available P supported optimum egg production from 20 to 70 weeks on CSM diets, while 0.20%
maintained body weight and tibia ash equal to the higher NRC (0.25%) and breeder recommendations
(0.45%).
Waldroup (2000) indicated that after 3 to 4 weeks of age the P needs of commercial broilers are
greatly reduced and that when birds consume a significant amount of feed there is little need for
supplemental P in a typical CSM broiler diet. While a small margin of safety is advisable for a
commercial flock, the literature supports the NRC recommendation.
Calcium added to broiler and laying hen diets as well as Ca bound in dicalcium monocalicum and
monocalicum dicalcium phosphates can reduce P utilization and allow it to pass through bird digestive
systems undigested. In a study by Van der Klis et al. (1996), phytate breakdown decreased from 34% on
the basal diet with 30g Ca/kg to only 10% on a diet with 40g Ca/kg.
Select feed ingredients with readily available P. A major impact can be made by selecting
ingredients with highly available P (HAP). Phytic acid or phytate P found in many cereal grains and plant
byproducts is in a form that birds do not absorb well. For example, the P in corn and SBM has a
biological value of only 30 and 25, respectively, and is only 19% and 20% available because of the large
phytate content. Compared with the P in animal meals and fish meal, which are almost 100% bioavailable, feeding cereals can contribute to manure P. However, feeding low-phytate grains offers
opportunities to reduce fecal P. Highly available P corn contains the same level of total P as normal
varieties, although the level of phytate P in HAP corn is only 35% versus 75% to 80% in other corn
varieties (Stillborn 1998). Unfortunately, these varieties of corn are not yet commercially available.
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Use effective vitamin D levels and compounds. Birds with a dietary deficiency of vitamin D
do not use P well, and a study from the University of Georgia suggests the active form of vitamin D
(found in bird bodies) is even more effective than the precursor form of vitamin D normally supplied in
poultry diets (cholecalciferol). Addition of 1,25-dihydroxy vitamin D3 to the feed reduced broiler phytate
P excretion by 35% and improved total P retention by more than 20% (Edwards 1993).
Use feed additives/enzymes to enhance P availability and retention. Cereal-based diets
for poultry can contain a high proportion of P in cereal grains as phytate P. Phytate chelates other
minerals, proteins, and starches, making them unavailable to the bird. To improve utilization, phytase
enzyme can also be added to poultry diets that contain high levels of phytate. Studies have demonstrated
that adding dietary phytase improves apparent ileal digestibility of phytate P as well as AAs in turkey
poults (Yi et al. 1996).
Boling et al. (2000) demonstrated a 50% reduction in fecal P in laying hens consuming a low-P
(0.10% available P) diet plus phytase (300 U/kg) compared to a normal commercial P level diet (0.45%
available P). The authors indicated that the CSM diet with added phytase supported optimal egg
production from 20 to 70 weeks of age. Similar studies have demonstrated that adding dietary phytase
improves phytate P utilization in broiler chickens (Simmons et al. 1990, Broz et al. 1994) compared to the
NRC-recommended nPP level of 0.45%. Yi et al. (1996) showed that adding 350, 700, and 1050 U
phytase/kg to a CSM diet with 0.27% nPP reduced fecal P excretions by 30%, 37%, and 41%,
respectively.
Studies by Zyla et al. (1995) demonstrated an advantage of enzymatic “cocktails” over phytase alone
for dephosphorylating CSM-based feeds for growing turkeys. Turkey poults fed the enzymatic cocktail
from 7 to 21 days of age performed as well as the NRC or positive control diet but retained more dietary
P (77%) compared to the NRC or positive control (31% and 42.75%, respectively). Greater retention of
Ca was also observed as a result of feeding the enzymatic cocktail (68.15% vs. 45.5% and 49%).
Angel (2001) determined the effect of dietary phytase and citric acid on nPP in feed for commercial
turkeys. Poults were fed a starter diet that met NRC (1994) recommendations until 8 days of age. Then
the birds were fed three levels of phytase (0, 300, and 600 FTU/kg) and four levels of citric acid (0%, 1%,
2%, and 3%) with a diet low in nPP (0.44%) and Ca (1.20%). Phytase and citric acid significantly
improved weight gain, feed conversion, feed/gain ratio, and toe and tibia ash.
Economics of Reducing N and P Excretion
Feed conversion is affected by a number of factors ranging from water management, light
management, temperature, etc., so these factors must be considered. Poultry are relatively efficient at
feed conversion; on average it takes eight pounds of feed to produce a four-pound bird (feed conversion
of 2.0). Assume a situation where a grower has a total capacity of 40,000 birds and an average body
weight of four pounds per bird and that the company pays 3.5 cents per live pound with a bonus of 0.1
cents per pound for every point of feed conversion better than the average of 2.00. A grower who brings
the flock in with a feed conversion of 1.95, will receive $800 in bonus pay (0.1 cents x 5 points x 160,000
live weight).
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Waldroup, P.W., J.H. Kersey, E.A. Saleh, C.A. Fritts, F. Yan, H.L. Stillborn, R.C. Crum, Jr., and V.
Raboy, 2000. Nonphytate phosphorus requirement and phosphorus excretion of broiler chicks fed diets
composed of normal or high available phosphate corn with and without microbial phytase. Poultry Sci.
79:1451-1459.
Wu, Z., L.D. Satter, R. Sojo, and A. Blohowiak. 1998. Phosphorus balance of dairy cows in early
lactation at three levels of dietary phosphorus. J. Dairy Sci. 81 (Suppl. 1):358.
Yi, Z., E.T. Kornegay, and D.M. Denbow. 1996. Effect of microbial phytase on nitrogen and amino acid
digestibility and nitrogen retention of turkey poults fed corn-soybean meal diets. Poultry Science 75:979990.
Zyla, K., D.R. Ledoux, A. Garcia, and T. Veum, 1995. An in vitro procedure for studying enzymatic
dephosphorilation of phytate in maise-soybean feeds for turkey poults. British J. Poultry Sci. 74:3-17.
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Appendix A: NRC Guidelines
The following tables summarize the NRC nutritional guidelines for dairy, beef, swine, and poultry.
These tables and additional information are available at the Federation of Animal Science Societies
website: http://www.fass.org.
Table A-1. Selected nutrient requirements of dairy cows as determined using sample diets. 1
Holstein, 1,500 lb,
average body condition,
65 mo age
90 Days in Milk
Early Lactation
Dry, Pregnant
270 Days in
Gestation
BW 1,656 lb
Milk yield, lb/d
55
77
99
120
55
77
DM intake, lb/d
44.7
51.9
59.2
66
29.7
34.3
30.1
Net energy, Mcal/lb
0.62
0.67
0.7
0.73
0.94
1.01
0.48
Diet % RDP
9.5
9.7
9.8
9.8
10.5
10.5
8.7
Diet % RUP
4.6
5.5
6.2
6.9
7
9
2.1
CP, %
14.1
15.2
16.0
16.7
17.5
19.5
10.8
Ca, %
0.62
0.61
0.67
0.60
0.74
0.79
0.45
a
P, %
0.32
0.35
0.36
0.38
0.38
0.42
0.23
b
Potassium , %
1.00
1.04
1.06
1.07
1.19
1.24
0.52
Sodium, %
0.22
0.23
0.22
0.22
0.34
0.34
0.10
Copper , ppm
11
11
11
11
16
16
13
Zinc, ppm
43
48
52
55
65
73
22
c
a Equivalent
to the sum of RDP and RUP only when they are perfectly balanced.
bHeat stress may increase the need for potassium.
cHigh dietary molybdenum, sulfur, and iron can interfere with copper absorption, increasing the requirement.
1Adapted from Tables 14-7, 14-8, and 14-9, Nutrient Requirements of Dairy Cattle. 7th Revised Edition, 2001. National Research
Council, National Academy of Sciences, National Academy Press, Washington, D.C. (J. H. Clark, Chair, Subcommittee on Dairy
Cattle Nutrition).
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Table A-2. Protein, Ca, and P requirements for growing and finishing beef cattle.1
Body Weight, lb
525
650
775
900
1025
1150
DM intake, lb/d
21.5
23.5
25.5
14
17
19.5
CP, lb/d
1.0
1.22
1.36
1.49
1.57
1.65
1.72
1.8
1.55
1.69
1.82
1.86
1.91
1.95
2.5
1.87
2.01
2.13
2.14
2.15
2.16
3.3
2.18
2.32
2.43
2.40
2.38
2.36
4.0
2.49
2.62
2.73
2.66
2.60
2.54
Ca, lb/d
1.0
0.04
0.04
0.05
0.05
0.00
0.05
1.8
0.06
0.06
0.06
0.06
0.06
0.06
2.5
0.08
0.08
0.08
0.07
0.07
0.07
3.3
0.10
0.09
0.09
0.09
0.08
0.08
4.0
0.11
0.11
0.10
0.10
0.09
0.09
P, lb/d
1.0
0.02
0.02
0.03
0.03
0.03
0.03
1.8
0.03
0.03
0.03
0.03
0.04
0.04
2.5
0.04
0.04
0.04
0.04
0.04
0.04
3.3
0.04
0.04
0.04
0.05
0.05
0.05
4.0
0.05
0.05
0.05
0.05
0.05
0.05
1Weight
at small marbling, 1,200 lb. Adapted from Nutrient Requirements of Beef Cattle 7 th Edition, 1996. National Research
Council, National Academy of Science, National Academy Press: Washington, D.C.
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Table A-3. Protein, Ca, and P requirements for beef cows. 1
_______________________________________________________________________________
Months
Since
Body
DM
CP
Calving
Weight
Intake
Ca
_
P
lb
lb
 lb/d 
0 (Calving)
1,340
24.6
2.20
0.06
0.04
1
1,200
26.8
2.71
0.08
0.05
2 (Peak Milk)
1,200
27.8
2.97
0.09
0.06
3
1,205
28.4
2.82
0.08
0.06
4
1,205
27.4
2.54
0.07
0.05
5
1,205
26.5
2.26
0.06
0.04
6
1,210
25.7
2.04
0.06
0.04
7 (Weaning)
1,215
24.2
1.45
0.04
0.03
8
1,225
24.1
1.49
0.04
0.03
9
1,240
24.0
1.57
0.04
0.03
10
1,260
23.9
1.69
0.06
0.04
11
1,290
24.1
1.89
0.06
0.04
1Mature
weight at body condition 5, 1,200 lb; peak milk, 20 lb; calf birth weight 85 lb; calving interval 12 months. Adapted from
Nutrient Requirements of Beef Cattle 7th Edition, 1996. National Research Council, National Academy of Science, National
Academy Press: Washington, D.C.
Table A-4. Selected nutrient requirements of pigs.1
Pig Weight
Nutrient
3-5 kg
(7-11 lb)
5-10 kg
(11-22 lb)
10-20 kg
(22-44 lb)
20-50 kg
(44-110 lb)
50-80 kg
(110-176 lb)
80-120 kg
(176-265 lb)
CP, %
26.0
23.7
20.9
18.0
15.5
13.2
Lysine,
% total
1.5
1.35
1.15
0.95
0.75
0.60
Lysine, % appt.
ileal dig
1.26
1.11
0.94
0.77
0.61
0.47
Ca, %
0.90
0.80
0.70
0.60
0.50
0.45
0.70
0.65
0.60
0.50
0.45
0.40
P, % avail.
0.55
0.40
0.32
0.23
0.19
0.15
Potassium, %
0.30
0.28
0.26
0.23
0.19
0.17
Sodium, %
0.25
0.20
0.15
0.10
0.10
0.10
Copper, mg
6
6
5
4
3.5
3
100
100
80
60
50
50
P, % total
Zinc, mg
1Adapted
from Tables 10-1 and 10-5 Nutrient Requirements of Swine. 10th Revised Edition, 1998. National Research Council,
National Academy of Sciences, National Academy Press: Washington, D.C. (G. L. Cromwell, Chair, Subcommittee on Swine
Nutrition).
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Table A-5. Selected nutrient requirements of poultry.1
LayerLayera,b
a,b
100
120a,b
Nutrient
Layer-80
Broiler
0-3 wk
Broiler
3-6 wk
Broiler
6-8 wk
Protein, %
18.8
15.0
12.5
23.0
20.0
18.0
Ca, %
4.06
3.25
2.71
1.00
0.90
0.80
P,%
0.31
0.25
0.21
0.45
0.35
0.30
Potassium, %
0.19
0.15
0.13
0.30
0.30
0.30
Copper, mg
?
?
?
8
8
8
Zinc, mg
44
35
29
40
40
40
0.19
0.15
0.13
0.20
0.15
0.12
c
c
Sodium, %
Turkey
Nutrient
0-3 wk
3-6 wk
6-9 wk
9-12 wk
12-15 wk
15-18 wk
Protein, %
28.0
26.0
22.0
19.0
16.5
14.0
Ca, %
1.2
1.0
0.85
0.75
0.65
0.55
0.6
0.5
0.42
0.38
0.32
0.28
0.7
0.6
0.5
0.5
0.4
0.4
Copper, mg
8
8
6
6
6
6
Zinc, mg
70
65
50
40
40
40
0.17
0.15
0.12
0.12
0.12
0.12
Duck
0-2 wk
Duck
2-7 wk
Duck
Breeding
Turkey
Tom
Turkey
Hen
Protein, %
22.0
16.0
15
12.0
14.0
Ca, %
0.65
0.60
2.75
0.50
2.25
c
0.40
0.30
?
0.25
0.35
Potassium, %
?
?
?
0.4
0.6
Copper, mg
?
?
?
6
8
Zinc, mg
60
?
?
40
65
0.15
0.15
0.15
0.12
0.12
P, %
c
Potassium, %
Sodium, %
Nutrient
P, %
Sodium, %
a Grams
feed intake per hen daily
b Based on dietary Metabolizable Energy concentration of approximately 2,900 kcal/kg (1318 kcal/lb) and an assumed rate of egg
production of 90% (90 eggs per 100 hens daily).
c Phosphorus is nPP.
1Adapted from Tables 2-3, 2-6, 3-1, and 5-1 Nutrient Requirements of Poultry, 9 th Revised Edition, 1994. National Research
Council, National Academy of Sciences, National Academy Press: Washington, D.C. (J. L. Sell, Chair, Subcommittee on Poultry
Nutrition).
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Questions
1. National Research Council (NRC) guidelines are:
a. Available for most livestock.
b. Inadequate for modern production systems.
c. Experimentally derived.
d. Both A and C
Answer: d
2. Feed waste is:
a. Minimal and unimportant in most operations.
b. Influenced by proper positioning of feeders.
c. Related to amino acid content.
d. None of the above
Answer: b
3. The nutrients of most environmental concern are:
a. Potassium and calcium.
b. Phosphorus and nitrogen.
c. Molybdenum and lysine.
d. All are environmentally important.
Answer: b
4. Feed conversion (ratios) for livestock and poultry commonly are:
a. Less than 1.0.
b. Less than 3.0.
c. Between 3.0 and 5.0.
d. Greater than 5.0.
Answer: b
5. Rumen Degradable Protein (RDP) is best described as:
a. Non-digestible protein.
b. Amino acid protein.
c. Readily available protein.
d. None of the above
Answer: c
6. A nutrient mass balance can be used to:
a. Measure nutrient excesses in the operation.
b. Determine amino acid content of feed.
c. Characterize digestibility.
d. Weigh silage.
Answer: a
7. Ruminants usually require inorganic P to be added to their diets.
a. True
b. False
Answer: False
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8. Phytate-P is important because it is:
a. The most available form of P for swine and poultry.
b. The most unavailable form of P for swine and poultry.
c. A major constituent of inorganic P.
d. None of the above
Answer: b
9. Diets formulated on the basis of crude protein (CP):
a. Are the most efficient of the various techniques.
b. Typically supply excesses of certain amino acids.
c. Are not used for beef production.
d. Both B and C
Answer: b
10. Major reductions in N and P excretion from swine are possible but are very expensive.
a. True
b. False
Answer: False
11. An important consideration when formulating diets to reduce P excretion is:
a. Animal health
b. Land available for manure application.
c. Cost of implementing the diet.
d. All of the above
Answer: d
12. Important amino acids include:
a. Lysine.
b. Phytase.
c. Methionine.
d. Both A and C
Answer: d
13. Phase feeding:
a. Is limiting access to feeders to certain times of the day.
b. Is a dietary program that changes with the animal's age and size.
c. Has had very limited success in reducing nutrient excretion.
d. Both A and C
Answer: b
14. Inorganic P is commonly added to poultry diets.
a. True
b. False
Answer: True
15. The Metabolizable Protein System:
a. Is more efficient than diets based on crude protein.
b. Considers all protein sources equal in value.
c. Attempts to maximize IUP.
d. Is less efficient than diets based on crude protein.
Answer: a
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16. When compared with NRC recommendations, diets at most dairies:
a. Include considerably less P.
b. Include considerably more P.
c. Include approximately the same amount of P.
d. Save money on P supplements.
Answer: b
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