Influence of SLA haplotype on ovulation rate and litter size in miniature pigs

Abstract

Systemic blood was collected from and surgery performed on sows of 3 strains of miniataure swine bred for specific SLA (swine MHC) haplotypes (a, c and d) from Day 2 to Day 6 after mating (first day of mating = Day 0). Ovulation rate was determined by counting corpora lutea and embryos were flushed from the uterus. Progesterone, oestradiol-17β and oestrone were quantitated in blood plasma and uterine flushings by RIA. SLA(d/d) females had higher ovulation rate than SLA(a/a) or SLA(c/c) females (11.50 ± 0.87 vs 9.11 ± 0.68 and 8.17 ± 0.83, respectively; P < 0.01). Oestrone was higher than oestradiol-17β in systemic plasma (56.5 ± 6.4 vs 33.0 ± 4.7 pg/ml, P < 0.01) while oestradiol-17β was higher than oestrone in uterine flushings (19.8 ± 1.4 vs 14.9 ± 1.5 pg/horn, P < 0.10). Systemic progesterone concentration was correlated with day after mating (r = 0.93, P < 0.01). There was no effect of haplotype on any of the hormone concentrations measured. Litter size was analysed from 99 matings amongst SLA(a/a), SLA(a/c), SLA(a/d), SLA(d/c) sires and dams. Litter size from -/d and d/d sows or from d/d boars were larger (P < 0.05) than for all other matings. Although ovulation rate was higher in SLA(d/d) sows, the significant effect of sire SLA genotype on litter size suggests an additional effect of the d haplotype on embryonic survival.