Nutrient Management Diet Modification

Terry J. Klopfenstein

University of Nebraska, Lincoln, Nebraska, U.S.A.


Animal feeding operations are becoming more concentrated and the U.S. EPA (Environmental Protection Agency) has proposed more restrictive requirements. Great progress has been made in diet modifications designed to reduce animal excretion of nutrients. The nutrients of primary concern are nitrogen and phosphorus.


Phosphorus (P) is an essential mineral nutrient required for bone growth and maintenance and for most body metabolic functions such as energy utilization. Phosphorus has been supplemented to animal diets in mineral form such as dicalcium phosphate produced from mined mineral deposits. Typically, phosphorus was fed above the requirement of the animals as a safety factor due to lack of confidence in the precise P requirements and supplies. P in manure can build up in soils and subsequently contaminate ground water if not properly managed. P requirements are quite different for ruminants (cattle and sheep) and nonruminants (pigs and chickens), and P is metabolized differently by ruminants.

Poultry and swine grow rapidly and therefore require high levels of P in their diets (up to .6% of diet;[1-3]). Much of the P in feed ingredients (such as corn and soybean meal) is in the form of phytate P. Swine and poultry lack the enzyme (phytase) necessary to utilize the phytate P so it appears in the manure. Inorganic P must be supplemented to meet the animal's requirements. This makes P use very inefficient (10 to 20%) and most of the P ends up in the manure. There are four technologies that producers can use to reduce P excretion.

1. Feeding to requirements. Ongoing research is helping to more precisely define P requirements for each type of production and for animal ages within each type of production. With modern technology, it is possible to formulate diets quite precisely so that P is not overfed.[1]

2. Phytase. This enzyme is produced commercially through microbial fermentations and can be added to swine or poultry diets. Phytase releases the organic P from phytate and makes it available to the animal.[4,5] Therefore, the phytate P in corn and soybeans, the primary feedstuffs in swine and poultry diets, is utilized to meet the animal's requirements, reducing the need for supplement.

3. Phase feeding. Swine and poultry grow rapidly. Bone growth is very rapid in young animals and is essentially zero in mature animals. Therefore, the requirement for P decreases as the animals grow and mature.[2,3] Phase feeding is the process of changing diets to reduce the amount of P. In the past, two or three diets may have been fed, but now the number is increasing to five or six. Phase feeding, combined with precise formulation and precise requirements, decrease dietary P and therefore manure P.[1]

4. Low phytate feeds. Genetically enhanced low-phytate corn and soybean meal are available. The total P in these feedstuffs is not necessarily lower, but the P is in the available, inorganic form rather than the organic (phytate) form.[1,6] Feeding low-phytate corn and soybeans can decrease P excretion by 50%.

Beef and dairy cattle digest and metabolize P somewhat differently than nonruminants. The microorganisms in the rumen digest the P in phytate, making the P available to the animal. Beef and dairy cattle tend to grow slower and have lower P requirements than nonruminants.[7,8] Lac-tating dairy cows excrete considerable amounts of P in milk so cows giving milk have higher requirements higher requirements for higher producers.[8]

The most important issue with ruminants is to establish precise requirements and then formulate diets to meet but not exceed requirements. The requirements for lactating dairy cows is about .30% of the diet.[9] The ingredients (corn, supplemental protein, silage, alfalfa) fed to dairy cows will supply most, if not all, of this requirement.

Beef cattle in feedlots are typically fed diets high in corn grain, which contains .25 to .3% P. Recent research suggests the requirement for feedlot cattle is .12 to 14%.[10] The problem is that the ingredients in the feedlot diets (primarily corn) have nearly .3% P. There does not seem to be any practical way of reducing dietary P levels below .25% and therefore, P excretion by feedlot cattle is relatively high.


Nitrogen (N) is a part of amino acids (AA) that form proteins required by all animals; animals consume protein and AA and then excrete various forms of N. If N in manure is not managed appropriately, it can contaminate surface and ground waters (nitrate). Just as important is the volatilization of N (NH3) from manure. The resulting NH3 (ammonia) adds to odors and can be redeposited on cropland or environmentally sensitive areas such as lakes and streams.

Swine and poultry must be fed essential AAs to meet requirements. Because of rapid lean growth, AA requirements are high and must be met to produce optimal body weight gains and feed efficiencies.1-2,3-1 However, if any AA is fed above the requirement, that AA will be used for energy and the N excreted.


The ideal protein is a protein with a balance of amino acids that exactly meets an animal's AA requirements.1-11-1 By formulating diets to ideal protein content, no excess AAs are fed and N excretion is minimized. Formulation for ideal protein can be accomplished by using high-quality protein sources with good balances of AA and protein sources that complement the AA balance in corn. The greatest opportunity is to use crystalline AA to balance for AA deficiencies. Lowering the dietary protein content by two percentage points and supplementing with crystalline AA results in a 20 to 25% decrease in N excretion in swine or 30 to 40% in poultry.[12]


Feed additives or feeding management systems that increase feed efficiencies also increase efficiency of N utilization. Ractopamine increases lean growth in swine and, therefore, increases N-use efficiency.1-1-1


Amino acid requirements decrease as swine and poultry grow, just as the P requirement decreases. Balancing diets to ideal protein and changing diets often as pigs or poultry grow decrease the protein fed and, therefore, the N excreted.[1]


Cattle are unique because of the microflora in the rumen. This ability allows them to digest fiber, but does raise some challenges in protein nutrition. Protein that reaches the small intestine is a combination of microbial protein and undegraded feed protein. This protein (metabolizable protein, MP) is digested and absorbed in a manner similar to nonruminants. The growing beef animal and lactating dairy cows have two requirements that nutritionists must meet degradable protein for the rumen microbes and undegraded protein that supplies the additional MP needed by the animal.[7,8] Only recently have these requirements been elucidated, and further refinement of requirements is needed.

The greatest opportunity for decreasing N excretion by cattle is to use the MP system to meet but not exceed requirements for degradable and undegradable protein. Phase feeding feedlot cattle and group feeding dairy cows have the potential to markedly reduce N excretion. Ammonia losses have been reduced by as much as 32% by using these technologies.1-13-1 There is some reluctance by nutritionists to reduce levels of degradable and undegradable protein because of concern that milk or beef production will be compromised. Research indicates that will not happen, but it is more difficult to control variables in commercial production facilities.[14-16]


Phosphorus and nitrogen excretion can be reduced markedly by the use of new technologies. In the future, there will be incentives for producers and nutritionists to make use of these technologies.


1. Klopfenstein, T.J.; Angel, R.; Cromwell, G.L.; Erickson, G.E.; Fox, D.G.; Parsons, C.; Satter, L.D.; Sutton, A.L. Animal Diet Modifications to Decrease the Potential for Nitrogen and Phosphorus Pollution; Council for Agricul tural Science and Technology: Ames, IA, 2002. CAST Issue Paper Number 21.

2. National Research Council. Nutrient Requirements of Poultry, 9th Ed.; National Academy Press: Washington, DC, 1994.

3. National Research Council. Nutrient Requirements of Swine, 10th Ed.; National Academy Press: Washington, DC, 1998.

4. Kornegay, E.T.; Denbrow, D.M.; Yi, Z.; Ravindran, V. Response of broilers to graded levels of microbial phytase added to maize soybean meal based diets containing three 11. levels of non phytate phosphorus. Br. J. Nutr. 1996, 75, 839 852.

5. Cromwell, G.L.; Stahly, T.S.; Coffey, R.D.; Monegue, 12. H.J.; Randolph, J.H. Efficacy of phytase in improving the bioavailability of phosphorus in soybean meal and corn soybean meal diets for pigs. J. Anim. Sci. 1993, 71, 1831 1840.

6. Cromwell, G.L.; Traylor, S.L.; White, L.A.; Xavier, E.G.; Lindemann, M.D.; Sauber, T.E.; Rice, D.W. Effects of low phytate corn and low oligosaccharide, low phytate 13. soybean meal in diets on performance, bone traits, and P excretion by growing pigs. J. Anim. Sci. 2000, 78 (Suppl. 2), 72. (abstract).

7. National Research Council. Nutrient Requirements of Beef Cattle, 7th Ed.; National Academy Press: Washington, DC, 1996. 14.

8. National Research Council. Nutrient Requirements of Dairy Cattle, 7th Ed.; National Academy Press: Wash ington, DC, 2001. 15.

9. Wu, Z.; Satter, L.D.; Blohowiak, A.J.; Stauffacher, R.H.; Wilson, J.H. Milk production, estimated phosphorus excretion and bone characteristics of dairy cows fed different amounts of phosphorus for two or three years. 16 J. Dairy Sci. 2001, 84, 1738 1748.

10. Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T.; Brink, D.; Orth, M.W.; Whittet, K.M. Phosphorus requirement of finishing feedlot calves. J. Anim. Sci. 2002, 80, 1690 1695.

Baker, D.H.; Han, Y. Ideal amino acid profile for chicks during the first three weeks posthatching. Poult. Sci. 1994, 73, 1441 1447.

Allee, G.; Liu, H.; Spencer, J.D.; Touchette, K.J.; Frank, J.W. Effect of Reducing Dietary Protein Level and Adding Amino Acids on Performance and Nitrogen Excretion of Early Finishing Barrows. In Proceeding of the American Association of Swine Veterinarians; Amer ican Association of Swine Veterinarians: Perry, PA, 2001; 527 533.

Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T. Dietary Protein Effects on Nitrogen Excretion and Volatilization in Open dirt Feedlots. In Proceedings of the Eighth Interna tional Symposium on Animals, Agriculture and Food Processing Wastes; ASAE Press: St. Joseph, MO, 2000; 204 297.

Satter, L.D.; Klopfenstein, T.J.; Erickson, G.E. The role of nutrition in reducing nutrient output from ruminants. J. Anim. Sci. 2002, 80 (E. Suppl. 2), E143 E156. Klopfenstein, T.J.; Erickson, G.E. Effects of manipulating protein and phosphorus nutrition of feedlot cattle on nutrient management and the environment. J. Anim. Sci. 2002, 80 (E Suppl. 2), E106 E114. Wang, S.J.; Fox, D.G.; Cherney, D.J.; Chase, L.E.; Tedeschi, L.O. Whole herd optimization with the Cornell net carbohydrate and protein system. III. Application of an optimization model to evaluate alternatives to reduce nitrogen and phosphorus mass balance. J. Dairy Sci. 2000, 83, 2160 2169.

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