Dietary protein effects on hen performance and nitrogen excretion.

Because dietary nitrogen intake affects nitrogen content in manure, diet management has been recognized as a means to reduce ammonia emissions from poultry operations. The objectives of the present research were 1) to determine the extent to which the CP content of laying diets can be reduced, based on performance criteria, and 2) to determine how ash:nitrogen ratios of manure, eggs, and hens are affected by dietary protein changes. Egg-type hens were fed equal daily amounts of essential amino acids in diets that provided 13, 15, or 17 g of protein/d. Each diet was fed to 20 hens, with 2 hens/cage. The planned digestible lysine intake was 0.71 g/hen per day. Ratios of other digestible amino acids to lysine were methionine plus cysteine, 0.83; threonine, 0.68; and isoleucine, 0.94. The experiment began when hens were 29 wk old and continued until they were 57 wk old. Egg production averaged approximately 90%, and daily protein intake caused no effects on egg production or grams of egg per hen per day. Feed intake was higher for hens fed 13 g of protein than for hens in the other 2 treatments (P < 0.01). Average feed intake for the experiment was approximately 95 g/d. Composition of the eggs was not affected by protein intake. Average values were DM, 30.5%; ash, 31.0% of DM; and nitrogen, 6.31% of DM. The average manure DM production was 25.9 g/hen per day, with an ash content of 25.5% of DM. Manure nitrogen content ranged from 3.98% of DM for hens fed 13 g of protein to 5.68% for those fed 17 g of protein (P < 0.01). A method is outlined that uses the analysis of fresh manure and manure leaving the poultry operation to estimate the loss of nitrogen as ammonia.