Direct and correlated responses to divergent selection for serum cholesterol concentration on day 56 in swine

Divergent selection for serum cholesterol concentration on d 56 was practiced in a four-breed, composite population for three generations. High and Low lines, representing high and low levels of serum cholesterol, respectively, were each maintained with approximately 10 males and 25 females per generation. Pigs from a contemporary Control line were evaluated only in the last generation. In the last generation, mean serum cholesterol concentration was significantly different among lines (107.1, 85.6, and 65.5 mg/dL for High, Control, and Low lines, respectively). Realized heritability was .31, .33, and .31 for high, low, and divergent selection (SE = .03), respectively. Terminal evaluation indicated that average birth and weaning (28 d of age) weight was lower (P < .05) for Low pigs (1.25 and 6.25 kg, respectively) than for High pigs (1.43 and 7.10 kg, respectively) and was intermediate for Control pigs (1.34 and 6.53 kg, respectively). At 56 d of age, High (15.1 kg) and Control (13.5 kg) pigs were heavier (P < .05) than Low pigs (11.9 kg). However, pigs sampled after 56 d did not differ (P > .05) in average daily gain, 164-d weight, feed consumption, or feed efficiency. Serum cholesterol concentration at 165 d of age was significantly different among lines (110.1, 98.5, and 85.6 mg/dL for High, Control, and Low pigs, respectively), although differences were smaller than at 56 d of age. When slaughtered at approximately 106 kg (188 to 195 d of age), Low pigs had significantly shorter carcasses than High and Control pigs (77.5 vs 78.7 and 78.9 cm, respectively). Low pigs had significantly more fat at the first rib (5.70 vs 5.28 cm) than High pigs. Lines did not differ significantly for fat thickness at the last rib, last lumbar vertebrae or 10th rib, or for longissimus muscle area. At 60 d of gestation, ovulation rate, measured as number of corpora lutea, was lower (P < .05) for High (9.84 eggs) than for Low (11.79 eggs) or Control (11.17 eggs) gilts. Differences in ovulation rate were reflected in smaller but nonsignificant differences in number of fetuses (7.97, 9.00, and 8.55 fetuses for High, Low, and Control, respectively).