Dietary energy and protein for growing pigs 2. Protein and fat accretion and organ weights of animals slaughtered at 20, 50, 80 and 110 kg live weight

This investigation was performed to study the effects of restricted versus ad libitum feeding on carcass composition, on protein and fat accretion and on body development and organ weights. The carcass composition was evaluated on 168 pigs by serial slaughter at 20, 50, 80 and 110 kg LW. The chemical composition was examined in only 62 of these animals. The carcasses were partitioned into four cuts and dissected into lean meat, fatty tissue, rind and bones. Ad libitium feeding resulted in daily weight gain exceeding restricted feeding in the three weight ranges by 42%, 17% and 7% and feed conversion ratios by 3%, 15% and 9%, respectively. Castrated males exceeded daily weight gains of females by 6%. At 20 kg the carcass moisture content was 65% for both sexes, which on average over feed regimens at 110 kg decreased to 56% and 52% for females and castrated males, respectively. Correspondingly, the carcass crude fat (CF) content increased from 13% to 24% and 30%, respectively. At 110 kg LW on restricted feeding the carcass meat content of females exceeded that of castrated males by 1.7, and on ad libitumfeeding by 3.9 percentage units; correspondingly, carcass fatty tissue of castrated males exceeded those values for females by 0.5 and 3.9 percentage units, respectively. Daily carcass crude protein (CP) accretion on ad libitum feeding for females and castrated males for the interval 22- 1 11 kg LW was, on average, 95 g. Daily caracass CF accretion on ad libitum feeding exceeded that on restricted feeding by 34%. Ad libitumfed castrated males and females showed daily CF accretion rates of 231 g and 158 g, respectively. Ad libitum feeding increased weights of liver over restricted feeding by 12% (P < 0.01) and kidneys by 21% (P < 0.001). Feed regimen also influenced CF content of muscles. It is concluded that feed regimen influenced carcass CP content at slaughter only to a limited extent, but greatly influenced daily CP accretion. However, carcass CF content and daily CF accretion were largely influenced by feed regimen and sex. These differences became manifest after 50 kg LW. Feed regimen also influenced liver and kidney weights.