Study on the oestrous synchronization in gilts by using progestin altrenogest and hCG: its effect on the follicular development, ovulation time and subsequent reproductive performance.

The aim of this study was to further investigate the effect of using progestin altrenogest and hCG to synchronize the oestrous cycle and its effect on follicular development, ovulation time and subsequent reproductive performance. Thirty crossbred gilts were divided into three groups. Group A (control) received a 5 ml of normal saline for 18 consecutive days by individually top-dressing. Groups B and C gilts received 20 mg (5 ml) of progestin altrenogest for 18 consecutive days by individually top-dressing. On day 3 (72 h) after withdrawal of progestin altrenogest, Group C gilts received hCG (500 IU, im). The follicular development and ovulation time were examined by transabdominal ultrasonography. Subsequent reproductive performances, i.e. number of total born per litter (NTB), number of live born per litter (NBA), number of stillbirth per litter (NSB), average piglet birth weight (ABW), lactation length (LL) and weaning to oestrous interval (WOI), were recorded. None of the gilts in Group A showed oestrus within 10 days after withdrawal of normal saline. Groups B (eight of 10) and C gilts (four of 10) came into oestrus at 5.6 +/- 0.5 and 6.5 +/- 0.6 days after withdrawal of progestin altrenogest, respectively. The ovulation time of Groups B and C gilts took placed at 25.0 +/- 4.7 and 25.0 +/- 5.0 h after standing oestrus, respectively. The pre-ovulatory follicular size (diameter) of Groups B and C gilts was 8.0 +/- 2.0 and 11.0 +/- 3.0 mm, respectively. A tendency of larger litter size (NTB) in Group B gilts was found when compared with Group A gilts. To conclude, using progestin altrenogest alone can be used to synchronize the oestrous cycle in gilts without unenthusiastic effect on the follicular development, ovulation time and subsequent reproductive performances. However, treatment of gilts with hCG at day 3 (72 h) after withdrawal of altrenogest had unenthusiastic effect on oestrus synchronization.