1Adapted from "Ohio Livestock Manure and Wastewater Management Guide".

0.1% NPP with no additional phosphate supplementation. Hens fed the diet with 0.1% NPP developed a phosphorus deficiency, as indicated by decreased rate of egg production, egg weight, feed consumption and increased mortality. Hens fed 0.2% NPP or more had similar performance. The addition of 300 units of phytase per kg of diet corrected the deficiency in the diet with 0.1% NPP. Phytase caused no beneficial effect when added to diets with 0.2% or more NPP. Feed consumption during the experiment was approximately 85 grams per day.

An experiment with brown egg layers also indicated a low NPP requirement (Um and Paik, 1999). Hens fed no supplemental phosphate (calculated NPP = 0.12%) plus 500 units of phytase per kg produced as well as those fed 0.26% NPP or 0.37% NPP. Feed consumption was approximately 114 grams per day.

These studies question the need for supplemental phosphate in hen diets. It appears that the amount of NPP supplied when meeting appropriate protein levels will meet a hen’s needs, if the diet also supplies phytase. The research reported above used either 300 or 500 units of phytase per kg of diet. That combination of NPP and phytase should result in good production and low levels of phosphorus in the manure.

Reducing nitrogen in the diet and manure of hens is more complicated than reducing phosphorus. Crude protein is calculated by analyzing for nitrogen and multiplying by 6.25. Most of the nitrogen is present in the amino group of amino acids, and most layer diets are formulated to provide specific amounts of amino acids to the hen each day.

Two concepts are useful when trying to decrease the amount of nitrogen in the feed and manure. One is that less nitrogen or protein is needed in the diet if good quality protein sources are used. If a protein source with high concentrations of limiting amino acids is used, less is needed to provide the required amounts of amino acids than would be required

1Adapted from Phytase in animal nutrition and waste management.

of a poor quality protein. For example, considerably more protein is needed to supply the

same amount of lysine if peanut meal is used (49.0% C.P., 1.54% lysine) than if soybean meal is used (48.5% C.P., 2.96 % lysine).

A second concept is that crystalline amino acids may be used to supplement limiting amino acids. Instead of using intact protein from corn and soybean meal to meet all amino acid needs, these protein sources may meet all amino needs except methionine. Crystalline methionine is added to meet that particular need. This practice usually reduces feed cost per ton and also reduces total dietary nitrogen. The second limiting amino acid is generally accepted to be lysine, followed by tryptophan and/or threonine. The availability of crystalline amino acids makes it possible to meet amino acid needs and reduce dietary nitrogen.

Commercial layer diets have substantially higher amino acid levels than are suggested by controlled experiments, thus supplying more dietary nitrogen. For example, Nutrient Requirements of Poultry (1994) lists a lysine requirement of 690 mg per day. Commercial layer diets often supply 750 to 800 mg of lysine per day from intact protein. There must be an unknown reason why diets with higher amino acid or protein levels give better results over a cycle of production.

We designed some research to re-examine the order of limiting amino acids in layer diets. The experiment used Hy-Line W36 hens and DeKalb XL hens. These strains were chosen because of their differences in daily feed consumption. When they were 32 weeks of age, they were fed low protein diets supplemented with amino acids to determine the requirement for valine and threonine. Appropriate amounts of corn, soybean meal, peanut meal and wheat were stored for use during the experiment and were analyzed for amino acid content.

After analysis, a diet that was low in valine was formulated to provide 0.56%, or 560 mg of valine per day for W36 hens eating 100 grams per day. XL hens were predicted to eat 110 grams per day, so their basal diet contained 0.51% valine. If they ate 110 grams per day, they would also consume 560 mg per day. All diets contained 20% wheat, 7% peanut meal and proportions of corn and soybean meal to provide the correct amount of valine. Crystalline valine was added to 4 other diets to supply a total of 630, 700, 770 and 840 mg of valine per day. Each diet was fed to two replicate groups of W36 hens and two groups of XL hens. Crystalline amino acids were supplemented to provide the following amounts

of other amino acids per day: isoleucine, 700 mg; lysine, 800 mg; methionine and cystine, 650 mg; phenylalanine and tyrosine, 1150 mg; threonine, 600 mg; and tryptophan, 180 mg.

A concurrent experiment determined threonine requirement. The basal diet was formulated to provide 380 mg of threonine per day with other diets providing 450, 520, 590 and 660 mg per day.

The experiments continued for 6 weeks, and information was collected to determine egg production, egg weight and feed consumption. The general result was that dietary levels of valine or threonine caused no significant effects through 4 weeks. Results from weeks 5 and 6 usually showed decreased egg production, egg weight and feed consumption when hens were fed too little of an amino acid.

After the valine and threonine experiments were completed, experiments with different levels of isoleucine, lysine and tryptophan were started. Hens from the first trial were fed a nutritionally adequate diet for three weeks and then assigned to subsequent treatments. The procedure was the same as described earlier. A basal diet was formulated to provide 450 mg of isoleucine, 560 mg of lysine, or 120 mg of tryptophan per day.

A broken line statistical procedure was used to estimate the amount of amino acid each day that was required to support a maximum rate of egg production or maximum egg yield per day. Average daily amino acid intake was plotted against egg production or daily egg mass to determine the amount of amino acid needed for maximum egg production or egg yield. Four estimates were derived for each amino acid. Two – maximum egg production and maximum egg yield – were estimated from data collected from the W36 hens. Two were estimated from the XL data. The four estimates were averaged to indicate the amount of each amino acid needed each day.

Results from the estimates were as follows: lysine, 652 mg; threonine, 523 mg; tryptophan, 143 mg; and valine, 654 mg. No estimate for isoleucine was derived because the basal diet that supplied 450 mg per day did not cause a significant depression in any production parameter in 6 weeks.

A conscious effort was made to avoid the term "requirement" for the estimates in the previous paragraph. The numbers are so low that commercial nutritionists might automatically condemn their validity. However, they are valid for calculating the order of limiting amino acids in a layer diet. All of the estimates are based on the same feed ingredients, the same hens and the same housing.

The order of limiting amino acids was calculated based on the assumption that sulfur amino acids are first limiting in a corn-soy layer diet. The order for lysine, threonine, tryptophan and valine can be calculated by finding the proportions of corn and soybean meal needed to meet the estimates determined experimentally. For example, Nutrient Requirements of Poultry (1994) indicates corn has 0.40% valine and soybean meal has 2.22% valine. If we assume corn and soybean meal will be 90% of a layer diet, we can solve the following equation:

The same calculations can be done with lysine, threonine and tryptophan. Results are in Table 3. Another series of calculations was completed using the amino acid analysis from corn and soybean meal used in the experiment. Those numbers for corn are 0.21% lysine, 0.25% threonine, 0.04% tryptophan, and 0.35% valine. For soybean meal the numbers are 2.96% lysine, 1.82% threonine, 0.65% tryptophan, and 2.25% valine.

Calculations shown in Table 3 suggest that threonine is the second limiting amino acid in a corn-soy layer diet. Valine appears to be the third limiting amino acid. Lysine and tryptophan share positions 4 and 5, depending on which amino acid composition is used for corn and soybean meal.

It appears that there is more work to be done in the area of protein/amino acid nutrition for layers. An egg weighing 61 grams contains 6.6 grams of protein (Stadelman and Cotterill, 1995). Why must we feed 16 to 18 grams of protein to get the transfer of 5 to 6 grams of protein to an egg each day? If we can make progress on that research question, we can decrease feed costs and also decrease the amount of nitrogen that passes through the hen and into the manure.