DEVELOPMENT OF A CALCULATION MODEL FOR PREDICTING THE AMOUNT OF N EXCRETED BY THE PIG - EFFECT OF FEEDING, PHYSIOLOGICAL STAGE AND PERFORMANCE

In highly intensive pig production areas, manure disposal is a major problem especially for nitrogen (N), in relation to water pollution by nitrates and gaseous ammonia emissions. In order to take precisely into account the effects of preventive measures (better adjustment of dietary protein supply, improvement of performance level), a prediction model has been developed for calculating total amount of N excreted by the pig at different physiological stages. N output (NO) was calculated on a daily basis as the difference between N intake and N retention. For gestation period, the model was based on a comprehensive literature analysis of the effects of protein and energy supply, parity number and gestation stage on N retention. During lactation, N balance was calculated from the results of a factorial study on amino acid requirements. During growing and finishing, N retention was calculated on a daily basis from daily weight gain and protein content of that gain. Protein content of the gain was determined from dissection and chemical analysis of 65 pigs differing in genotype, weight and sex. A single allometric relationship, taking into account EC carcass muscle percentage at 100 kg body weight (BW), was established between body N mass and BW (R2=0.98). The mathematical model allows calculation of total N output from criteria easily accessible at the farm level. The results of different simulations confirm the possibilities to reduce NO through nutrition and show that NO can vary widely according to performance, even in practical conditions.