Printer Friendly

Chapter 7 Proteins.

It has long been known that all animals must receive in their food at least a certain minimum amount of protein. More recently, investigations have shown that for man and for such animals as swine, poultry, dogs and rats, the quality or kind of protein is fully as important as the amount.



Protein supplements generally constitute the highest-cost ingredients of finished feeds. For this reason, it is important that the purchaser of feeds understand the nature of the requirement for protein. In fact, protein is probably not required at all by any species of livestock. Rather, it is the amino acids that constitute the feedstuff protein that are required by livestock. In ruminant nutrition, the production of microbial protein must be managed to maximize productivity and profitability.


About 15 percent of body weight is due to protein. This protein is distributed throughout the body in tissues, enzymes, and hormones.

Protein sources for livestock rations are more expensive than carbohydrate sources. In fact, protein is usually the most costly component of a finished feed. Because of this, a purchased feed product is often identified by its percent protein content.

A major goal in protein nutrition is to create a ration that enables the animal to capture feed protein in animal flesh or animal product efficiently. The more efficiently dietary protein is captured, the less protein needs to be in the ration to achieve a given level of productivity. If the ration is not properly balanced for nutrients, a significant amount of the feed protein may not be captured. This uncaptured protein will be removed from the body, primarily by the kidneys, in the form of ammonia (fish), urea (mammals), or uric acid (poultry). The nitrogen in these excretory products is a significant source of environmental pollution.

In order to support efficient production and/or growth, rations must be balanced such that the levels of energy and protein each support similar levels of performance. A protein shortage relative to energy results in increased fat deposition because the ration energy cannot be used to synthesize protein tissue--the energy is put into storage for later use. The use of body fat to meet the body's need for energy is very inefficient and an excessive reliance on fat stores of energy will lead to health problems.

Applying a knowledge of protein nutrition to ration formulation then, has three benefits: (1) it maximizes profitability by optimizing the use of expensive dietary protein, (2) it minimizes the risk of nitrogen pollution, and (3) it helps maintain animal health.


Proteins are organic compounds containing carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. The distinguishing feature of protein molecules is the nitrogen content. The nitrogen in protein molecules is found in the amino groups of amino acids. An amino group is comprised of a nitrogen atom bonded to two hydrogens,--N[H.sub.2]. In addition to an amino group, amino acids have a carboxylic acid group,--COOH, hence the name amino acid. In amino acids, both the amino group and the carboxylic acid are bonded to the same carbon. The other two entities bonded to this carbon are a hydrogen atom and an R group. The R group varies with the amino acid (Figure 7-1).

A protein molecule can be visualized as a long chain or several chains of amino acids joined together by linkages. These chains are folded in complex ways, creating the three-dimensional structure that is an important characteristic of proteins. The properties of a protein molecule are determined by the number, type, and arrangement of the amino acids that comprise the protein.

The linkages between amino acids are called peptide bonds (Figure 7-2). The terms peptide and polypeptide refer to chains of amino acids that are shorter than normally found in protein molecules.




There are 22 amino acids found in body proteins. For most species of livestock, about half of these can be manufactured by the body if supplied with extra amino groups or nonspecific nitrogen sources. These are called nonessential or dispensable amino acids. The remaining amino acids either cannot be made by the animal or cannot be made at a rate sufficient to support maximum performance. These are called essential or indispensable amino acids. They must be provided by either diet or the synthetic activities of microbes inhabiting the digestive tract. In discussing dietary protein sources, protein quality refers to the content of essential amino acids in the feedstuff. Figures 7-3a to 7-3j show the structure of the classic 10 essential amino acids. Memorization is helped by the phrase PVT TIM HALL (phenylalanine, valine, theonine, tryptophan, isoleucine, methionine, histidine, arginine, leucine, lysine).







Taurine (Figure 7-3k) is another amino acid. Among domestic livestock, it is a dietary essential only for the cat. The structure of taurine is shown in Figure 7-3k.

There are some amino acids that, for some species of livestock, do not fit neatly into the essential and nonessential categories. A dietary proline requirement has been established for chicken broilers, but not for layers or other types of livestock. Methionine is an essential amino acid and cysteine is not. However, animals make cysteine from dietary methionine. Therefore, to ensure that that the animal receives adequate amounts of both methionine and cysteine, the diet either has to have enough methionine to meet both the methionine and cysteine requirements, or a lower amount of methionine and enough cysteine proper. This is of nutritional significance in the dog, pig, chicken, and fish because these animals receive minimal amino acids from microbial activity in their digestive systems, and because the requirements for methionine and cysteine for these animals are known. It should be mentioned that cysteine often occurs in proteins in its oxidized form, cystine, in which two cysteine molecules are bonded together through formation of a disulfide group.

As methionine is to cysteine, so phenylalanine is to tyrosine: given excess phenylalanine, livestock can make tyrosine. Either the diet has to have enough phenylalanine to meet both phenylalanine and tyrosine requirements, or a lower amount of phenylalanine and enough tyrosine proper.







In poultry, glycine can be synthesized, but the rate is not sufficient to support maximum growth. Excess serine can be converted to glycine so poultry nutritionists monitor the glycine + serine level in the diet of growing birds.


Most of the protein in animal diets must be digested and hydrolyzed into the component amino acids in order to pass out of the digestive tube and into the blood (Figure 7-4). The exceptions are the peptides that may originate in the feed or may result fromincompletely digested feed proteins. Absorbed peptides are responsible for food allergies but their nutritional significance is largely unknown. As is the case with monosaccharides, some amino acids are absorbed via the sodium pump. The sodium pump is described in Chapter 6 and illustrated in Chapter 9, Figure 9-3.

Most of the amino acids absorbed come from feed protein, but some come from the proteins of the animal's own tissue that have been sloughed off from the epithelium lining the digestive tube and from the enzymes of digestive secretions. This is referred to as endogenous protein. Endogenous protein, in grams, is calculated as 4.72 x dry matter fed in kilograms (dairy NRC, 2001). In the companion application to this text for dairy, beef, sheep, and goats, calculations of available metabolizable protein (MP) use the sum of MP from the rumen microbes digested, MP from feed protein that was not degraded by the rumen microbes, and MP from endogenous protein.

In swine nutrition, the issue of amino acid bioavailability is addressed using ileal digestibilities. A feedstuff with known amino acid content is fed to swine that have been fitted with a cannula in the ileum. Ileal contents are collected and analyzed for amino acid content. The proportion of each amino acid that is not collected is referred to as the apparent ileal digestibility for that amino acid in that feedstuff. If this proportion is corrected for endogenous losses of amino acids, it is referred to as true ileal digestibility. The companion application to this text for swine uses true ileal digestibility.

Once absorbed, amino acids are used to build the proteins of the animal's body. Virtually every tissue in the animal body contains protein, and all cells synthesize proteins for part or all of their life cycle. In addition, some of the body's hormones and all the body's enzymes are made of protein.


Livestock require essential amino acids in their diets and sufficient nonspecific sources of nitrogen with which to make the nonessential amino acids. Whether these come from the protein in soybean meal, alfalfa hay, or meat meal makes no difference. In fact, in the swine, poultry, fish, and pet food industries, it is routine to meet some of the essential amino acid requirements by including crystalline amino acids in the feed formula. For the most part, however, it is still most economical to meet the amino acid requirements of livestock by formulating a ration that contains a combination of natural protein sources. An example is shown in Figure 7-5. By themselves, blood meal, soybean meal, and corn meal are either excessive or deficient in lysine and methionine for a 55-lb. growing pig, but a combination of these protein sources provides the proper amino acid balance.


The microbial populations living in the digestive tracts of livestock are capable of making all amino acids needed by livestock. These amino acids are incorporated into the cells of the bacteria. If these bacterial populations exist downstream from the small intestine, the animal will probably not have access to these amino acids except through coprophagy (consumption of feces). If, as is the case with ruminants, the microbial population exists upstream from the small intestine, some of the bacteria will regularly pass through the small intestine and their component amino acids will be absorbed. Due to the synthetic activity of bacteria in the rumen, there are no amino acids that are dietary essentials for healthy, mature ruminant animals. In fact, the rumen microbes can make essential amino acids from nitrogen sources that are not even in protein form.

This is not to say, however, that protein quality is not an issue in ruminant nutrition. As described in Chapter 4, feed protein is broadly classified as degradable and undegradable. The undegradable protein is unavailable to the microbes of the rumen. This is termed bypass protein, undegradable intake protein (UIP) as contrasted with degradable intake protein (DIP), or rumen undegradable protein (RUP) as contrasted with rumen degradable protein (RDP). Because RUP in ruminant diets arrives at the small intestine unaltered by microbial activity, its initial quality determines its ultimate value. To maximize the delivery of amino acids to the mammary gland of high-producing dairy cows, 35 percent or more of the dietary protein may need to bypass the rumen.

Identifying what portion of feed protein should be RDP and what portion should be RUP is a major focus of ruminant nutrition. Nitrogen fractions or "pools" have been identified in feedstuffs. There are two systems of protein pools currently in use in dairy nutrition: the dairy NRC system and the CNCPS 4.0/beef NRC (2000) level II system (Figures 7-6 through 7-9).

The CNCPS 4.0/Beef NRC Level II Protein Pools

In the Cornell Net Carbohydrate and Protein System (CNCPS 4.0) as well as the beef NRC (2000) level II, the protein pools are characterized using an in vitro method (Sniffen et al., 1992). The in vitro method used by CNCPS gives five protein pools: A, B1, B2, B3, and C. Protein pool Acontains the nonprotein nitrogen (NPN). Protein pool B1 contains the rapidly degraded true protein. Protein pool B2 contains true protein and large peptides that are potentially degradable. Protein pool B3 contains slowly degradable protein. Protein pool C contains undegradable, largely indigestible protein (Figures 7-6 and 7-7).

The Dairy NRC Protein Pools

In the dairy NRC (2001), the protein pools are characterized using an in situ method. The in situ method used by the NRC defines the protein pools as: A, rapidly degraded; B, potentially degradable; and C, undegradable (Figures 7-8 and 7-9). The various methods used to characterize protein in ruminant nutrition have been reviewed (Schwab et al., 2003).

Figure 7-7

Components of the protein
pools (determined using an in
vitro method) used in the beef
NRC, 2000 level II and
CNCPS 4.0.
Source: National Research Council,
2000 (beef NRC level II) and Fox et
al., 2000 (CNCPS 4.0).

* Protein pool A
  --Nonprotein nitrogen (NPN)
    * Ammonia
    * Peptides, amino acids
      --Rapidly converted to ammonia by and for ruminal microbes
    * Much of the degradable crude protein in preserved forages is NPN
* Protein pool B1
  --True protein, rapidly degraded to ammonia
    * Most of the degradable protein in pasture is B1
* Protein pool B2
  --True protein, potentially degradable
    * Competition between digesta passage rate (Kp) and feedstuff
      protein B2 pool digestion rate (Kd) determines fate of protein
      pool B2
* Protein pool B3
  --True protein, mostly undegradable
    * B3 protein is associated with cell wall
      --Measured as neutral detergent insoluble protein less
        acid detergent insoluble protein (NDFIP - ADFIP)
    * Lots of B3 in treated protein supplements
    * Lots of B3 (a large % of total, though total may be low) in some
      forages, fermentation co-products, animal protein co-products
* Protein pool C
  --True protein, resistant to mammalian and microbial enzymes
  --Measured as acid detergent insoluble protein (ADFIP)
    * Most of the protein associated with lignin in cell walls
    * Most of the protein associated with Maillard products
    * Most of the protein in tannin-protein complexes

In both the dairy NRC and CNCPS 4.0/beef NRC level II systems, there is a protein pool that is potentially degradable. To determine whether this protein pool becomes a part of RDP or RUP, a calculation of feed passage rate (Kp) is used. Kp is used by both the dairy NRC and CNCPS 4.0/beef NRC level II systems. It is the percent per hour disappearance rate for a given feedstuff, and it is calculated based on the characteristics of the entire ration. High-producing dairy cows fed large amounts of grain will have rapid passage rates and high Kp values. Dry cows receiving large amounts of dry hay will have slow passage rates and low Kp values.

This text and the dairy ration application use the protein pools system as defined in the dairy NRC publication. All discussion that follows pertains to the dairy NRC (2001) system.

The contribution of absorbed protein from pool B in a given feedstuff is determined using the predicted passage rate of the ration (Kp) and the inputted degradation rate, percent/hour of the feedstuff's protein pool B (Kd). Kd is a characteristic of each feedstuff, and as such, is an inputted value. Kp is calculated for each feedstuff based on feedstuff type. The formulas used to calculate feedstuff Kp in the dairy NRC (2001) and in the companion application to this text are shown in Figure 7-10. Afeedstuff with a slow rate of pool B degradation, Kd, in the ration of a cow experiencing a rapid feed passage rate, Kp, will have a large RUP component in its B fraction. A feedstuff with a rapid rate of pool B degradation in the ration of a cow experiencing a slow feed passage rate will have a large RDP component in its B fraction. The formula used to calculate the percentage RUP in the crude protein of a given feedstuff is:

RUP = B [Kp/(Kd + Kp)] + C

Figure 7-9
Components of the protein
pools (determined using an
in situ method) used in the
dairy NRC publication

* Protein pool A

    --Non-protein nitrogen (NPN)

       * Ammonia

       * Peptides, amino acids

         --Rapidly converted to ammonia by and for ruminal microbes

       * Much of the degradable crude protein in preserved forages is

    --True protein, rapidly degraded

      * Most of the degradable protein in pasture is true protein,
        rapidly degraded to ammonia

* Protein pool B

     --True protein, potentially degradable

       * Competition between digesta passage rate (Kp) and feedstuff
         protein B pool digestion rate (Kd) determines fate of protein
         pool B

* Protein pool C

    --True protein, undegradable

       * Digestible

         --Lots of digestible C in treated protein supplements

         --Lots of digestible C (a large % of total, though total may
           be low) in some forages, fermentation co-products, animal
           protein co-products

* Indigestible

    --Resistant to mammalian and microbial enzymes

      * Most of the protein associated with lignin in cell walls

      * Most of the protein associated with Maillard products

      * Most of the protein in tannin-protein complexes

Figure 7-10
Feedstuff passage rate
formulas (Kp) from the dairy
NRC 2001. DMI: Dry matter
intake; BW: body weight.

For wet forages: Kp - 3.054 + (0.614 x DMI % BW)
For dry forages: Kp - 3.362 + (0.479 x DMI % BW) - (0.017 x NDF %) -
  (0.007 x % concentrate)

For concentrates: Kp - 2.904 + (1.375 x DMI % BW) -
  (0.020 x % concentrate)

Figure 7-11
How the dairy NRC
calculates RUP and RDP in
a feedstuff

Determining the RUP of blood meal in the following ration fed to a
lactating dairy cow: legume hay 3 lb., mixed hay 5 lb., mixed silage
30 lb., corn silage 35 lb., corn meal 20 lb., soybean meal 3 lb.,
distillers grains 2 lb., blood meal 0.5 lb., mineral/vitamin 1.5 lb.


Table values for blood meal:
Protein pool B = 39.9% of crude protein
Protein pool C = 50.0% of crude protein
Kd (rate of degradation of the B fraction) = 1.9%/hr.

Passage rate of blood meal based on the above ration:
Kp (rate of passage from the rumen) = 7.39%/hr.


    RUP = {B x [Kp / (Kd + Kp)]} + C
        = {39.9 x [7.39 / (1.9 + 7.39)]} + 50.0
        = [39.9 x (7.39 / 9.29)] + 50.0
        = (39.9 x 0.80) + 50.0
        =  31.92 + 50.0
        =  81.92

This is the % of the crude protein of blood meal in the above diet that
behaves as RUP. The % RDP in the crude protein of blood meal in the
above diet is  100-%RUP = 18.08.

This formula is used in an example in Figure 7-11. Because RUP and RDP are expressed as percent of crude protein, and because crude protein is either RUP or RDP, RDP may be calculated as 100 - % RUP.

In addition to passage rate, feed processing affects degradability of the B pool. Heat treatment of whole oilseeds and solvent-extracted oilseed meals shifts the potentially degradable B pool toward the undegradable end of the spectrum.

Feedstuff protein of the A pool and the degradable protein portion of the B pool constitute the rumen degradable protein. Ration RDP results in microbial growth in the rumen. Aportion of the microbes are regularly washed out of the rumen and digested, and their amino acids are made available to the ruminant. Amino acid content of microbial protein, as well as that of animal tissue and bovine milk, is shown in Table 7-1.

Feedstuff proteins that fall into the undegradable portion of the B pool and the C pool make up the RUP. The digestible portion of the RUP will result in amino acids being delivered directly to the blood.

The total amino acids absorbed by ruminant animals will be the sum of that from bacteria, digestible RUP, and endogenous protein. Protein nutrition in the ruminant animal involves managing the protein pools to ensure optimum delivery of both microbial protein and digestible RUP to the small intestine.


It is often possible, for a given ration, to identify which amino acid is falling farthest from its requirement. This amino acid is said to be first limiting. The first limiting amino acid is not necessarily the one required in the greatest quantity or the one least prevalent in the ration. By identifying the first limiting amino acid, the nutritionist has identified a factor that may be limiting performance. If other nutrients are in excess of the requirement, adding more of the first limiting amino acid to the ration may result in improved performance.

With monogastric species, the first limiting amino acid is often added to rations to improve the efficiency of protein utilization. In usual rations for horses, fish, and swine, the first limiting amino acid is lysine. For poultry, the first limiting amino acid in usual rations is methionine. Dog rations are variable to the extent that it is difficult to identify a "usual" ration. The first limiting amino acid for a given dog food formulation may be lysine, methionine, or another amino acid.

In swine nutrition, the concept of first limiting amino acid has been expanded to what is called the ideal protein. The ideal protein is the optimum dietary ratios of essential amino acids relative to lysine. These ratios are established for the functions of maintenance, protein accretion, and milk synthesis, and are shown in Table 7-2. In swine diets formulated on an ideal protein basis, amino acids are provided in the exact proportions required, and in this way, every amino acid is equally limiting. Formulating diets based on the ideal protein should reduce the amount of excess amino acids that are catabolized (Lopez et al., 1994).

In dairy nutrition, the matter has been extensively studied and the first limiting amino acid does not appear to be limiting production in usual dairy rations. In other words, the performance supported by the first limiting amino acid in ruminant animals is usually in excess of that supported by other nutrients. Supplying more of the first limiting amino acid, therefore, usually does not improve performance. The amino acids most often predicted to be first limiting in dairy rations are methionine, lysine, and, collectively, the branched chain amino acids (valine, leucine, and isoleucine). It is interesting to consider the challenges involved in developing an amino acid supplement for ruminant animals. The product must be resistant to microbial degradation, yet absorbable at the small intestine.


Table 7-3 gives crude protein requirements predicted by NRC tables and formulas for selected domestic animals. These requirements are expressed in terms of pounds and in terms of the percent of the dry diet. Remember that protein is the package in which are found the amino acids that are required by the animal. For most livestock species, the minimum protein requirement is determined from the animal's requirement for both the essential amino acids and the nitrogen sources needed for the manufacture of nonessential amino acids.

In examining Table 7-3, it is important to keep in mind the factors that determine how much protein an animal will require.

1. Growing animals accrete protein and because they have not yet reached mature body size, growing animals have relatively low dry matter intakes. Growing animals therefore require diets that contain a greater concentration of protein than do mature, idle animals.

2. Mature animals that are not pregnant or lactating use dietary protein only to maintain body tissues and replace protein secretions. The protein concentration required for mature, idle animals may be half that required for growing or producing animals.

3. Herbivores have evolved to use carbohydrate in the plants they eat as their primary source of energy. Because carnivores eat animals and few plants, their natural diet includes relatively little carbohydrate, but a relatively large amount of protein and fat. Table 7-4 gives a comparison of the two feed types. Because of the differences in diet, carnivores have evolved to use protein and fat as their primary sources of energy. Domestic carnivores, therefore, are fed diets containing much more protein than would be needed to build the body's protein tissue. It has become apparent, however, that domestic carnivores can use more carbohydrate than would be present in the diet of their wild counterparts. Since carbohydrate is less expensive than protein, some carbohydrate is usually included in the diets of domestic carnivores.

The Consequences of Feeding Excess Protein

All absorbable amino acids are absorbed. In other words, even if the amount of amino acids flowing through the small intestine is more that what the animal can use, all amino acids will, in most cases, still be absorbed. Absorbed amino acids are transported from the blood into the cells. Recall that the sodium pump is involved in this transport for some amino acids. Inside the cells, the breakdown of excess amino acids yields amino groups and carbon skeletons. The carbon skeletons resemble carbohydrates and are used by the animal as a source of energy. The amino groups are unstable and they are quickly converted to ammonia (N[H.sub.3]). But ammonia is toxic to cells, so it is expelled back into the blood. In fish, the ammonia is excreted at the gills. In poultry, the ammonia is converted in a complex series of reactions to uric acid prior to excretion. In mammals, the bloodstream carries the ammonia to the liver. There, the enzymes of the urea cycle convert the ammonia to urea. The urea is then released into the blood, where most of it is filtered out at the kidneys and sent to the bladder for excretion. The operation of the urea cycle and the conversion of ammonia to uric acid require energy. In mammalian livestock, the energy used to process the nitrogen in unused amino acids is referred to as the urea cost. The urea cost becomes part of the animal's maintenance energy requirement, leaving less energy available to support other functions. In the companion application to this text for dairy and beef cattle, the urea cost is calculated and added to the maintenance energy requirement.

The elevated blood levels of urea that result from feeding excess protein have been associated with health and reproductive problems in some species. The effects of excess dietary protein are discussed in Chapter 18 and are illustrated in Figure 18-5.

The processing of extra absorbed protein is not totally efficient, and heat is generated. Feeding excess protein to a hot animal (due to high ambient temperature or high work level) can make it even more challenging for the animal to maintain normal body temperature.

If a protein excess occurs as the result of an excess amount of purchased protein supplement being fed, there is an economic consequence to feeding excess protein. Finally, animals fed protein in excess of their requirement may present an environmental threat due to the effects of excreted nitrogen in the environment.


Protein nutrition in livestock rations involves providing livestock with sources of essential amino acids and nonspecific nitrogen sources with which to build the nonessential amino acids. When absorbed, amino acids provide the building blocks for the construction of protein in animal tissues and products. Ruminant nutrition involves managing the flow of protein in two sources: the microbes grown on RDP and the bypass protein or RUP.


1. Explain the following statement: "Protein is probably not required by any species of livestock."

2. Name the classic 10 essential (or indispensable) amino acids.

3. Explain the relationship between the amino acid methionine (essential) and the amino acid cysteine (nonessential). Explain the relationship between the amino acid phenylalanine (essential) and the amino acid tyrosine (nonessential).

4. In protein nutrition, animals require the essential amino acids and a supply of nonspecific sources of nitrogen. Why do animals require nonspecific sources of nitrogen?

5. Explain why, in ruminant nutrition, the protein quality of the rumen undegradable protein is more important than the protein quality of the rumen degradable protein.

6. Explain the concept behind the protein pools as applied by the dairy and beef NRC committees.

7. Which of the dairy NRC protein pools is affected by feed passage rate? Which of the CNCPS protein pools is affected by feed passage rate?

8. Explain the term ileal digestibility as it is used in amino acid nutrition of swine.

9. Explain the ideal protein concept as applied to swine nutrition.

10. What becomes of the protein that is ingested in excess of the animal's requirement?


Fox, D. G., Tylutki, T. P., Van Amburgh, M. E., Chase, L. E., Pell, A. N., Overton, T. R., Tedeschi, L. O., Rasmussen, C. N., & Durbal, V. M. (2000). The net carbohydrate and protein system for evaluating herd nutrition and nutrient excretion (CNCPS version 4.0). Animal Science Department Mimeo 213, Cornell University, Ithaca, NY.

Lopez, J., Goodband, R. D., Allee, G. L., Jessee, G. W., Nelssen, J. L., Tokach, M. D., Spiers, D., & Becker, B. A. (1994). The effects of diets formulated on an ideal protein basis on growth performance, carcass characteristics, and thermal balance of finishing gilts housed in a hot, diurnal environment. Journal of Animal Science 72, 367-379.

Morrison, F. B. (1949). Feeds and feeding (21st ed.). Ithaca, NY: Morrison Publishing Co.

National Research Council. (2000). Nutrient requirements of beef cattle (7th revised edition.). Washington, DC: National Academy Press.

National Research Council. (2001). Nutrient requirements of dairy cattle (7th revised edition). Washington, DC: National Academy Press.

National Research Council. (1998). Nutrient requirements of swine (10th revised edition.). Washington, DC: National Academy Press.

Schwab, C. G., Tylutki, T. P., Ordway, R. S., Sheaffer, C., & Stern, M. D. (2003). Characterization of proteins in feeds. Journal of Dairy Science 86(E. Supplement), E88-E103.

Sniffen, C. J., O'Connor, J. D., Van Soest, P. J., Fox, D. G., & Russell, J. B. (1992). A net carbohydrate and protein system for evaluating cattle diets. II. Carbohydrate and protein availability. Journal of Animal Science 70, 3562-3577.
Table 7-1
Amino acid contents
expressed as percent of
essential amino acids of
tissue, milk and rumen

                  Bovine       Bovine          Rumen
Amino acid        Tissue       Milk         Bacteria (1)

Arginine           16.8          7.2           10.2
Histidine           6.3          5.5            4.0#
Isoleucine          7.1         11.4           11.5
Leucine            17.0         19.5           16.3#
Lysine             16.3         16.0           15.8#
Methionine          5.1          5.5            5.2
Phenylalanine       8.9         10.0           10.2
Threonine           9.9          8.9           11.7
Tryptophan          2.5          3.0            2.7
Valine             10.1         13.0           12.5

(1) Bacteria values in bold type indicate amino acid content is
below that of both tissue and milk protein.

Source: National Research Council, 2001.

Note: Bacteria values in bold type indicate amino acid content
is below that of both tissue and milk protein indicated with #.

Table 7-2
The ideal protein for swine,
expressed as ratios of amino
acids to lysine

                                          Protein       Milk
Amino acid                  Maintenance   Accretion   Synthesis

Lysine                          100          100         100
Arginine                       -200 (1)       48          66
Histidine                        32           32          40
Isoleucine                       75           54          55
Leucine                          70          102         115
Methionine                       28           27          26
Methionine + cystine            123           55          45
Phenylalanine                    50           60          55
Phenylalanine + tyrosine        121           93         112
Threonine                       151           60          58
Tryptophan                       26           18          18
Valine                           67           68          85

(1) The negative value for arginine indicates metabolic synthesis
in excess of maintenance requirement.

Source: National Research Council, 1998.

Table 7-3
Crude protein requirements
for selected animals. (1) Percent
values are given on a dry
matter basis.


Fish, channel catfish, 100 g body weight           0.00198
Fish, rainbow trout, 100 g body weight             0.00114
Chicken, broiler, 5 wks. of age                    0.0603
Chicken, white egg layer, 3 lb. body weight        0.0331
Pig, growing, 45 lb. body weight                   0.45
Dog, growing, 30 lb. body weight                   0.08
Cat, growing kitten, 4.2 lb. body weight           0.04
Rabbit, growing, 5 wks of age                      0.0517
Horse, light work, 1,100 lb. body weight           2.23
Goat, maintenance, 88 lb body weight               0.14
Ewe, maintenance, 110 lb body weight               0.21
Beef animal, growing, 800 lb. body weight      See note below
Dairy cow, lactating, 1,400 lb. body weight    See note below

                                                Required (%)

Fish, channel catfish, 100 g body weight            30.00
Fish, rainbow trout, 100 g body weight              41.11
Chicken, broiler, 5 wks. of age                     22.22
Chicken, white egg layer, 3 lb. body weight         16.67
Pig, growing, 45 lb. body weight                    16.92
Dog, growing, 30 lb. body weight                    10.51
Cat, growing kitten, 4.2 lb. body weight            24.00
Rabbit, growing, 5 wks of age                       17.55
Horse, light work, 1,100 lb. body weight             7.64
Goat, maintenance, 88 lb body weight                 9.04
Ewe, maintenance, 110 lb body weight                 9.40
Beef animal, growing, 800 lb. body weight      See note below
Dairy cow, lactating, 1,400 lb. body weight    See note below

(1) Note: In beef and dairy nutrition, the protein "requirement"
would depend on the energy level of the ration. The protein in
the ration should be what is necessary to support a similar level
of performance (gain or milk production) to that supported by the
energy in the ration.

Table 7-4
Comparison of animal and
plant composition

                       % in Meat and Bone     % in Orchardgrass
                         Meal Tankage,         Hay,Early Bloom,
                          IFN 5-00-387           IFN 1-03-425
Nutrient Component     (dry matter basis)     (dry matter basis)

Protein                        50                    12.8
Fat                            12                     3
Minerals                       28                    8.5
Other (including              9.6                    75.8
COPYRIGHT 2006 Delmar Learning
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2006 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Tisch, David A.
Publication:Animal Feeds, Feeding and Nutrition, and Ration Evaluation
Geographic Code:1USA
Date:Jan 1, 2006
Previous Article:Chapter 6 Carbohydrates.
Next Article:Chapter 8 Lipids.

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters