Effects of Dietary Protein and Energy Levels on Cow Manure Excretion and Ammonia Volatilization

Adjusting dietary composition is considered an effective way to reduce nutrient losses to the environment. The effects of various dietary protein and energy levels on manure composition (Ca, Mg, K, Na, N, P, and pH) were studied by determining total and direct available ( free) nutrient concentrations in 8 slurries obtained from a feeding trial. Furthermore, the effects of dietary changes on NH3 volatilization from manure slurries were studied. Increasing the crude protein (CP) content of the feed (108 to 190 g/kg of dry matter) resulted in an average increase in total N and P content of the slurries of 56 and 48%, respectively. Feeding the cows more energy (5,050 to 6,840 kJ/kg of dry matter) increased total N and P content of the slurries by 27 and 39%, respectively. Total ammoniacal nitrogen (TAN) amounted to 52 to 77% of the total N content present in manure slurries. A low protein content or a low energy content of the diets reduced TAN concentrations in the slurries by 43% ( CP) or 25% ( energy). Changes in the protein content or the energy content of the feed did not significantly affect the free: total ratios of Na, Ca, and Mg content of the slurries. In agreement with the calculated NH3,aq ( aqueous) content, the total amount of NH3 volatilized from manure slurries was much greater (on average 10 times greater) when the cows were fed greater levels of CP. Although the slurries contained more TAN when cows were fed diets richer in energy, NH3 volatilization from the slurries was lower.