Development and simulation of a model for predicting nitrogen excretion in growing and finishing pigs

Abstract

In Japanese highly intensive pig production areas, the amount of nitrogen from manure exceeds and it results in serious environmental problems such as water pollution by nitrates and gaseous ammonia emissions. Although reduction in crude protein (CP) in diets is a procedure to decrease nitrogen excretion, some literatures indicated that it might lead to increase back fat thickness in carcass. In this study, a model was developed especially to investigate the effects of CP contents in diets on the utilization of nitrogen by growing and finishing pigs and their back fat depth. First, the nitrogen balance was calculated on the daily basis as the difference between nitrogen intake and retention, and then accumulated during growing and finishing period (body weight of 30 kg to 105 kg). The two indices used as a measure of the environmental load in this study were total nitrogen excretion / total nitrogen intake (I₁) and total nitrogen excretion / total nitrogen retention (I₂). The different simulations showed that decreases in I₁ and I₂ resulted from reduced CP contents in diets, when feeding levels are moderate and high. Remarkable decreases of back fat thickness in carcass were achieved, when feeding level was low. The results also suggest that the effect of CP content in diets on environmental load and production could vary widely according to energy contents and feeding levels.