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 800IU eCG was then injected 24h later, followed by 500IU hCG 48h 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 24h 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.

Selection of impubertal gilts by ultrasonography optimizes their oestrus, ovulatory and fertility responses following puberty induction by PG600.

In a group of gilts, occurrence of puberty is spread over several weeks. The optimal time to apply puberty induction is therefore difficult to define, as treatment of puberal gilts is meaningless. Changes in uterine aspect around puberty can be detected by ultrasonography. Two experiments were carried out to assess the effect of PG600(®) (400 UI of eCG and 200 UI hCG) administration to 6 months old gilts shown to be impubertal by ultrasonography on cyclicity and reproductive performance. Impubertal Large White gilts (n=94) were treated with either PG600 or solvent (controls). Administration of PG600 to impubertal gilts increased significantly the proportion of females displaying pubertal uterine ultrasound images 3 days after treatment (100% versus 65% in controls). The number of days to puberty was significantly reduced in gilts injected with PG600 (3.3 days) versus controls (4.7 days). In gilts of the PG600 group, ovulation rate was higher at the 1st oestrus compared to the 2nd, while this did not happen in controls. Progesterone concentrations were higher at mid-luteal phase in the PG600 treated gilts compared to controls (significant treatment by time interaction). Similar proportions of gilts returned to oestrus (89% versus 74% for controls). Following insemination at the 2nd oestrus, pregnancy rate and number of live embryos were unaffected by treatment. The combination of ultrasonography and PG600 optimizes the use of exogenous hormones by targeting treatment to gilts that need it, therefore facilitating the introduction of gilts into all in/all out system.