The interaction between ovulation rate and embryo survival in determining prolificacy of different strains of obese swine with gene polymorphisms for leptin receptors

Abstract

The Mediterranean Iberian pigs show a clear predisposition to obesity, due to gene polymorphisms for leptin receptors, and a lower prolificacy when compared with lean breeds. Previous studies indicate a bimodal effect of obese genotypes on prolificacy; either by lowering ovulation rate or by increasing embryo losses when compared with lean genotypes. The present study aimed to discriminate the relative influence of both parameters by comparing strains of Iberian females with different prolificacy (14 original purebred Retinto, group R, and 20 Retinto × Torbiscal females selected for prolificacy, group RT). Examination of ovaries around Day 40 of pregnancy showed a higher ovulation rate in the RT than in the R sows (21.5 ± 1.4 versus 12.3 ± 1.0 corpora lutea, respectively; P < 0.0005). However, there was a higher incidence of implantation failures and early embryo losses in the RT females (42.9 versus 14% for the group R; P < 0.005). Thus, the number of viable embryos was higher in the RT line (10.8 ± 0.5 versus 7.6 ± 0.7 in the R sows, P < 0.0005), but also limited when compared with ovulation rate. Conversely, this effect was not found in the R sows; however, prolificacy of these females was limited by higher embryo mortality (24.1 versus 4.6% for RT females). In conclusion, the present study evidences dissimilar reproductive behaviour among strains of the Iberian pig differing in prolificacy and confirms previous evidences suggesting the existence of intrinsic factors avoiding excessively large litter sizes in Iberian females.