The application of low crude protein wheat-soyabean diets to growing and finishing pigs 1. The effect on the growth performance and carcass characteristics of boars and gilts

Diets containing 131.6, 162.7, 192.4 and 207.3 g/kg dietary crude protein (CP) (treatments A, B, C and D, respectively) were fed to growing and finishing pigs (37.8 to 96.1 kg live weight) to evaluate the effect on growth performance, plasma ammoniacal nitrogen (PAN) and carcass characteristics. Dietary CP content was adjusted by altering the ratio of wheat to soyabean meal in the diet. Lysine, threonine, tryptophan and total sulphur-containing amino acids were included in all diets at concentrations equivalent to that in the highest CP diet. All diets provided 9.7 MJ/kg of net energy. Sixty pigs, blocked by initial live weight and sex, were randomly assigned to four dietary treatments (nine boars and six gilts per treatment). Pigs were individually fed, twice daily. The concentration of dietary CP did not affect feed intake or daily gain, but the feed conversion ratio (FCR) deteriorated as the concentration of dietary CP decreased (linear, P < 0.01). PAN concentration increased with dietary CP concentration in boars (linear, P < 0.001) and gilts (linear, P < 0.01). Dietary CP concentration did not affect carcass weight or kill-out proportion. Pigs fed diet A had lower (P < 0.05) lean meat proportion and greater (P < 0.05) backfat depth than pigs fed diet D. Carcass FCR deteriorated as CP concentration decreased (linear, P < 0.05). In conclusion, reducing the concentration of dietary CP resulted in a deterioration of FCR and carcass FCR.