GENETIC, SEX AND DIET EFFECTS ON PIG GROWTH AND FEED USE

SUMMARY Direct and interaction effects of breed of dam, line of pig, sex of pig and diet on growth, feed consumption and feed conversion were investigated in a 2 x 2  2 x 3 factorial arrangement of treatments. Each of the 24 subclasses consisted of two pens, each with two pigs, on test from 8 weeks of age to 100 kg in weight. Pigs were allowed ad libitum one of three corn-soybean meal diets containing (1) 12% crude protein, (2) 16% crude protein or (3) 12% crude protein plus supplemental lysine and methionine to approximate their levels in diet (2). Duroc and Yorkshire parents were crossed reciprocally within low-fat lines or control lines from a previous long-term study in which selection was based on backfat thickness. Breed of dam (B) had no significant effect on average daily gain (ADG), but crosses with Duroc dams ate more feed per day (ADF) and had poorer feed conversion ratios (FC) than pigs with Yorkshire dams. Control-line crosses had higher ADG and ADF than low-fat crosses, but the crosses did not differ in FC. Barrows averaged higher in ADG and ADF than gilts, but sex (S) effects on FC were essentially zero. Diets 2 and 3 did not differ for ADG or FC, but both exceeded diet 1 for these traits. B  line of pig (L) interaction effects were nonsignificant. L  S effects were significant for ADG; B x S, L  diet (D) and S x D interactions significantly affected FC. Low-fat crosses had better FC on diet 2, but control-line crosses were more efficient in FC on diet 1. Barrows had better FC than gilts on diet 1, but no significant sex differences in FC were noted on diets 2 and 3.