Effect of hCG administration at the onset of oestrus on early embryo survival and development in Meishan gilts

Abstract

A study was designed to advance the time of the ovulatory luteinizing hormone (LH) surge in Meishan gilts by human chorionic gonadotrophin (hCG) administration at the onset of oestrus and assess the effect on embryo survival and development. Twelve Meishan gilts were observed six times daily for oestrous behaviour and bred at 24, 36 and 48 h after observed oestrous onset. Six of those gilts were administered an ovulatory dose of hCG (500 IU) at observed oestrous onset. Blood samples were collected at oestrous onset (Day —2) and on Days 0, 2, 6, 9, 13, 16, 20, 23, 27 and 30 of gestation. All gilts were slaughtered on Day 30 of gestation and embryo survival and conceptus development assessed. Ovulation rate did not differ between control and hCG treated gilts (18.5 and 17.7 respectively; P>0.1) while the number of live conceptuses per gilt (17.2 and 12.8 respectively; P<0.08) and embryo survival rate (92.1 and 75.8% respectively; P<0.1) both tended to be reduced by the hCG treatment. Placental weight (17.2 and 23.1 g; P<0.01) was significantly increased in hCG treated gilts, while embryo weight (1.2 and 1.4 g; P<0.06) and placental length (42.8 and 47.2 cm; P<0.07) both tended to be increased in hCG treated gilts. Crown rump length ( P>0.1) and allantoic fluid volume ( P>0.1) did not differ between the treatment groups. Serum progesterone concentrations did not differ with treatment overall ( P>0.1) but were significantly elevated ( P< 0.05) at 48 h postoestrus in the hCG treated gilts compared to control gilts. Overall, these results indicate that advancing the time of the LH surge to oestrous onset, as in European breeds, compromised embryo survival and suggests that the longer time interval between oestrous onset and ovulation is important for the high rate of embryo survival in the Meishan pig.