PERFORMANCE OF PIGS FROM 2 GENOTYPES IN RELATION TO THE AMINO-ACID CONTENT OF THE DIET

Ninety-six female pigs comprising equal numbers of purebred Large White and crossbred Large White x Pietrain were used to assess the effect of genotype and the response of growing-finishing pigs to dietary amino acid concentration according to a 2 genotypes x 4 dietary treatments factorial design. Four sequences of two diets (one growing and one finishing diet) all based on cereals, peas, peanut meal and amino acids, with increasing contents of essential amino acids but with the same crude protein content and balance between essential amino acids were compared. Lysine contents ranged from 7.6 to 10.5 g/kg (2.3 to 3.2 g/Mcal DE) during the growing period (25-60 kg) and 6.6 to 9.6 g/kg (2.0 to 2.9 g/Mcal DE) during the finishing period (60-100 kg). The crude protein content was 155 g/kg during the growing period and 145 g/kg during the finishing period. Pigs were housed individually and fed the experimental diets twice daily according to a low energy feeding scale. Crossbred pigs had a lower feed conversion ratio and a higher growth rate, and at slaughter leaner carcasses than Large White pigs. No genotype x dietary sequence interaction was detectable in any criteria measured. In both periods, increasing the essential amino acid content led to a significant increase in growth rate up to a plateau. However, there were few differences in carcass composition, according to dietary sequence. It seems that with fast-growing pigs, under restricted feeding, the use of high levels of balanced amino acids can be advised, up to about 9.5 g lysine/kg (2.9 g/Mcal DE) during the growing period and 8.5 g lysine/kg (2.65 g/Mcal DE) during the finishing period.