Influence of SLA haplotype on preimplantation embryonic cell number in miniature pigs

Embryonic cell number in miniature pigs inbred for specific SLA haplotypes (a, c, and d) was determined on Day 6 by nuclear staining and, on Days 9 and 11, by DNA analyses (first day of oestrus = Day 0). Pigs exhibiting first behavioural oestrus at 08:00 h were hand-mated to an SLA homozygous boar 12 and 24 h later. Numbers of embryos flushed from uteri at 08:00-10:00 h on Days 6, 9 and 11 were greater (P less than 0.05) for SLAd females than for SLAa or SLAc females, which did not differ (8.2 vs 6.8 and 6.2, respectively). Recovery rates (embryos recovered/CL number) were similar, averaging 75.8% for all three SLA haplotypes. Embryos from SLAd dams contained fewer blastomeres (23 cells) on Day 6 than did embryos from SLAa (89 cells) or SLAc (79 cells) females. The reduced cell numbers of SLAd vs SLAa or SLAc embryos continued to Day 9 (28 vs 107 and 67 ng DNA/embryo) and Day 11 (167 vs 674 and 586 ng DNA/embryo). These results suggest an effect of the SLA complex on preimplantation embryonic development.