Genetic and non-genetic parameters related to embryo production in superovulated Large White (LW) gilts

The aim of this study was to identify genetic and non genetic factors which might affect results of embryo production of Large White (LW) cyclic gilts from data collected in one herd during 6 years. Donors (n = 1060) were synchronized with a progestogen treatment and luteolysis was induced 13-15 days later by 2 injections of cloprostenol. To stimulate follicular development 800 IU eCG was then injected 24 h later, followed by 500 IU hCG 48 h later. Donors were inseminated twice; depending on the onset of oestrus, the interval between hCG treatment and first insemination (hCGAI1) was either 24 or 41 h. Embryos were collected at 5-6 days after the 1st AI by flushing uterine horns. Traits of interest were the number of corpora lutea (CL), the number of flushed embryos (FE), the number of transferable embryos (TE) and the number of unfertilized embryos (UE). The average number of TE was 18.8 ± 9.0. The main sources of variation for CL, FE and TE were the season (P ≤ 0.002) and hCGAI1 (P ≤ 0.001) effects. For the interval of 24 h of hCGIA1 the number of TE was increased by 4 compared with the TE obtained for the 41 h interval of hCGIA1. Maternal and paternal genetic effects were estimated using restricted maximum likelihood methodology applied to the univariate animal model, whereas genetic covariance components were estimated in bivariate models. Estimates of maternal heritability were 0.45 for CL, 0.32 for FE, 0.29 for TE and 0.05 for UE whereas for the paternal effect, heritabilities were very low (<0.06). Genetic correlation between CL, FE and TE variables were very high (>0.89) for the maternal effect. A breeding scheme based on CL selection in response to superovulation could thus improve the number of transferable embryos.