The effects of expander processing and by-product inclusion levels on performance of grower-finisher pigs

Seventy-two entire male pigs (initially 28 kg body weight) were used to study the effects of by-product (pollard, rapeseed meal, peas and copra meal combined) inclusion level with or without expander processing, on growth performance and nutrient digestibility in a 3 X 2 factorial arrangement of treatments. Productive performance and nutrient digestibility coefficients (no. = 6) were determined in individually fed pigs offered pelleted diets ad libitum containing a low by-product diet (350 g/kg), medium by-product diet (520 g/kg) and high by-product diet (752 g/kg). The expanded diets were processed at 105 degrees C for 5 s at 35 bar pressure having been previously conditioned at 85 degrees C for 5 s. All diets were formulated using standard values for ingredients to have similar concentrations of digestible energy (DE) and ideal protein. Starch contents of 437, 401 and 314 g/kg and crude fibre contents of 48, 58 and 74 g/kg were recorded for the low, medium and high by-product diets respectively. No by-product level X expander processing interactions (P > 0.05) were observed in growth criteria, carcass characteristics or nutrient digestibility. Expander processing decreased (P < 0.05) the apparent organic matter (OM), ash and energy digestibility of the diets, as well as the digestible energy content of the diets. The level of by-product in the diet had no statistically significant effect on the OM, protein and energy digestibility or the DE content of the diets. The increase in by-product inclusion levels decreased (P < 0.05) average daily gain (ADG) (0.899 v. 0.888 v. 0.854 (s.e. 0.014) kg/day) from 28 kg to slaughter and food intake (1.62 v. 1.48 v. 1.48 (s.e. 0.028) kg/day) in the 28 to 55 kg weight range. Expander processing had no effect on ADG, food intake or food conversion ratio. The increase in by-product level decreased (P < 0.01) killing-out proportion (723 v. 705 v. 710 (s.e. 3.94) g/kg) and carcass ADG (0.684 v. 0.651 v. 0.635 (s.e. 0.012) kg/day) (P < 0.05). Expander processing decreased (P < 0.05) killing out proportion (707 v. 718 (s.e. 3.22) g/kg). In conclusion, increasing the by-product content of the diet decreased ADG while expander processing had no effect on growth performance.