How Much of Individual Nutrientsis Excreted by Dairy Cows?
Historically, the nutrient excretion standards most often used in the design of manure management systems were those of the American Society of Agricultural Engineers (ASAE, 1990). These standards are based on body weight of cows, however, they do not account for the large variation among dairies in nutrient excretion levels. The variation is caused by differing voluntary feed intake, differing supplemental levels, and differing amounts of nutrients harvested in the milk. Recent University of Florida experiments (Morse, 1989; Tomlinson et al., 1996) showed that N and P excretions by dairy cows varied dramatically with level of N and P intakes. These data confirmed that excretion estimates for individual farms are best based on dietary intake of a nutrient minus the amount secreted into milk. Most dairy farms have accurate estimates of feed and milk and, thus, this method of predicting total excretion of minerals by dairy cows is used in this publication ( Table 1 ). In Table 1 , the fo
