Response analysis of the Iberian pig growing from birth to 150 kg body weight to changes in protein and energy supply1

Abstract

A total of 251 growing-finishing Iberian (IB) pigs, 32 of which were suckling piglets, were used in 5 separate sets of trials. The comparative slaughter procedure was used to determine nutrient and energy retention at several stages of growth from birth to 150 kg BW. A factorial arrangement was used within each set of trials, involving several concentrations of ideal protein in the diets as 1 factor and 2 or 3 levels of feed intake as the other. The main objective of these studies was to derive the optimal protein-to-energy ratio in the diet to allow for the expression of maximum protein deposition rates. The effect of feed restriction on growth performance, protein deposition, and fat deposition was also assessed. According to allometric equations, empty BW (EBW) was related to whole body components or total chemical constituents of empty body mass (P < 0.001). For pigs receiving solid feed, highly statistically significant multiple regression equations were constructed, which derived nutrient (g/kg) or energy (MJ/kg) composition as a function of EBW, dietary protein-to-energy ratio, and level of feeding (P < 0.001). In pigs offered adequate protein-to-energy diets, ADG at each stage of production was predicted as a function of the average BW and feeding level (P < 0.001). It was observed that the estimates of ME required for maintenance and net efficiency of utilization of ME for growth change were within rather narrow ranges throughout the growth stages studied. Preferred values (413 kJ/kg BW(0.75) × d(-1) and 0.593 for ME(m) and k(g), respectively) were obtained by regressing total energy retention (kJ/kg BW(0.75) × d(-1)) against ME intake (kJ/kg BW(0.75) × d(-1)). A multiple-regression approach revealed that in the IB pig, ME costs for protein deposition and fat deposition reach 60 and 62 kJ/g, which is considerably greater than in conventional or lean pig genotypes. In the IB pig, the maximum daily rate of protein deposition (PD(max), g) seemed to follow a linear-plateau shape with a breaking point at 32.5 kg BW, beyond which PD(max) remained at an average rate of 75 g × d(-1). The marginal efficiency of body protein deposition was estimated at each growth stage. In pigs fed on optimal or suboptimal protein-to-energy diets, the relationship between PD and ME intake declined, following a curvilinear pattern with increasing BW; thus, implying relative increases in lipid gain as BW increased.