In studies on reducing crude protein in swine diets, researchers at Michigan State University have found that nitrogen excretion and ammonia can be reduced without affecting the growth rates.

The research tested six diets on six, 90-lb. pigs. The diets included 15% crude protein (CP) corn-soybean diet; 12% CP plus crystalline amino acids (CAA) diet; 9% CP plus CAA diet; 6% CP plus CAA diet; a protein-free diet and a casein-based diet containing 15% CP.

The 15% CP corn-soybean diet is typical and meets the requirements for growing pigs. The reduced CP levels contained the same corn-soybean meal ratio and were supplemented with CAA to maintain the ideal protein pattern. The protein-free and casein diets served as negative and positive controls.

Casein, a milk protein, has protein digestibility of 98%. Both the casein and protein-free diets were used to estimate the amount of endogenous nitrogen loss and its contribution to ammonia production.

The pigs were housed in metabolism crates, where total urine and feces were collected from each pig over five-day periods, pooled by pig and treatment after each experimental period and frozen.

The samples were mixed into slurries and incubated for 31 days. Ammonia (NH3) production was measured and odor panel tests conducted.

The preliminary data showed a reduction in the NH3 levels, tested for three consecutive days after the 31 days of anaerobic storage.

Results show a 63% reduction in NH3 in the 12% CP diet as compared to the 15% CP diet. The 9% CP plus CAA and the 6% CP plus CAA diets had similar reductions. NH3 reduction was the greatest in the protein-free diet. The NH3 production in the casein-based diet was similar to the 15% CP diet. Researchers note that despite the high digestibility of a feed ingredient, the endogenous nitrogen can contribute to NH3 production.

The results show nitrogen retention was similar for each diet except the 6% CP plus CAA diet, where retention was decreased. The pigs had a similar growth rate while on the 15% CP, 12% CP plus CAA and 9% CP plus CAA diets. Growth was depressed on the 6% diet.

Researchers: Emily Otto, Mel Yokoyama and Nathalie Trottier, Michigan State University. Phone Trottier at (517) 432-5140, or e-mail trottier@msu.edu.