model using body condition score is recommended (NRC, 2001a) for predicting body protein directly. Breeding cattle were assumed to have a condition score of 3.0 on a 5-point scale, and finished cattle were assigned a score of 4.25. Compositions of poultry carcasses as a percentage of live weight were based on reports by Wolynetz and Sibbald (1986) and Van der Hel et al. (1992) for starters, Brady et al. (1978) for growing, and Santoso et al. (1995) for mature broilers. Composition of layers was based on Katanbaf et al. (1989).

For cattle, the protein accretion associated with live weight gain was summarized by previous National Research Council (NRC, 2000, 2001a) publications. For the young calf (less than 30 percent of mature body weight), nitrogen retained for growth is assumed to be 3.0 g per 100 g live weight gain (National Research Council, 2001a). Using typical growth rates for cattle (0.83 kg/d), protein accretion per kilogram live weight gain was calculated according to the model defined by the National Research Council (2000). For swine, the protein as a percentage of live weight gain (grams per 100 grams of gain) was estimated as the derivative from Figure D-1 based on carcass data. For poultry, data on total carcass composition at maturity were used and divided by the weight change during growing.

All calculations were made according to recommendations in the body of this report. Current feeding recommendations were assumed in order to calculate excretion patterns in different types of livestock. These approximations may vary