Reproductive, endocrine, and organ weight differences of swine selected for high and low serum cholesterol

Three generations of selection for 56-d blood cholesterol concentrations were used to establish low and high cholesterol lines of pigs in which cholesterol concentrations differed by 39% in the last generation. Litter size (number of fully formed pigs born per litter) diverged with each successive generation of selection and, at the third generation, litter size differed between the low and high line by two pigs (high line = 8.5 +/- .6; low line = 10.5 +/- .5; P < .05). A random selection of offspring (gilts, n = 109; boars, n = 46; barrows, n = 94) from the third generation and a control line maintained throughout the experiment were monitored for hormonal and anatomical relationships that might provide insight into the mechanisms that altered fecundity. Ovulation rate (number of corpora lutea) as determined on d 60 of pregnancy was increased in the low (n = 29) compared with the high cholesterol line (n = 38; 11.8 +/- .3 vs 9.8 +/- .3, respectively; P < .05), and litter size continued to be increased in the low cholesterol line (P < .05). No differences were noted between lines in kidney, ovarian, or total corpora lutea weight. Empty uterine weight and adrenal weight were increased in the high cholesterol line (P < .05) in randomly selected offspring of the third generation, and liver weight increased in the low line (P < .05). Associated with increased concentrations of cholesterol were increased serum concentrations of progesterone (gilts) and testosterone (boars) in the high cholesterol line (P < .05). Serum concentrations of FSH were increased in gilts of the low cholesterol line (P < .05). Serum inhibin concentrations were increased in the high cholesterol line of boars (n = 18 for high and low cholesterol lines; P < .05). Serum growth hormone concentrations did not differ between genetic lines. Collectively, these data provide substantial evidence that high and low cholesterol lines differ genetically in ovulation rate and litter size, and that the mechanism relates to altered pituitary secretion of gonadotropin and altered feedback effects of increased or decreased steroid/inhibin synthesis by the gonad, much of which may be associated with altered cholesterol availability.