PS3-2. Dietary Protein Concentration and Electrolyte Balance Affect Urine pH, Nitrogen Excretion, and Manure Odorous Compounds in Growing Pigs

Abstract The objective of the present work was to investigate the interactive effects of lowering dietary crude protein (CP) concentration and dietary electrolyte balance (dEB) on urine pH, slurry pH, nitrogen (N) balance, and odorous compounds from manure in pigs. Twelve barrows with an initial body weight of 31.6 kg (standard deviation = 1.9) were allotted to a replicated 6 × 4 incomplete Latin square design to obtain 8 observations per diet. Six corn-soybean meal-based diets were prepared in a 2 × 3 factorial arrangement with 2 dietary CP concentrations (16% and 13%) and 3 dEB levels (145, 40, and –65 mEq/kg). The daily feed allowance was 3 times the metabolizable energy requirement for maintenance and provide to the animals with 2 equal meals at 0900 and 1800 h. Each experimental period consisted of a 4-d adaptation period, a 24-h slurry collection period, and a 4-d fecal and urine collection period. During the 24-h slurry collection on d 5, feces and urine were mixed at the fecal weight-to-urine weight ratio to obtain slurry sample. On each day during the 5-d collection period, fresh urine pH was instantly measured when pigs urinated shortly after the meal and collected urine pH was measured in the urine cumulatively collected in each bucket until the next meal. As the dEB was reduced, the fresh and collected urine pH quadratically decreased (P 0.05), and the quadratic effect was more pronounced in the 13% CP diets compared with the 16% CP diets (quadratic interaction; P 0.05). Slurry pH in pigs fed the 13% CP diets was less (P 0.001) than those fed the 16% CP diets. Slurry pH linearly decreased (P 0.001) as the dEB decreased. An interaction between dietary CP and quadratic response of dEB was observed for daily urinary N output (P = 0.016). Fecal N output was reduced by lowering dietary CP concentration (P = 0.025). Interactive effects between dietary CP concentration and the quadratic effect of dEB were observed on the acetate, propionate, and valerate concentrations in slurry (P 0.05). In conclusion, lowering dietary CP concentration or dEB decreased the urine pH, slurry pH, and daily N excretion in growing pigs. The quadratic decrease in both fresh and collected urine pH was more pronounced in the pigs fed the low-CP diets. Furthermore, interactive effects of dietary CP concentration and dEB were observed on the acetate, propionate, and valerate concentrations in the slurry from the growing pigs.