Ovulatory response of different GnRH analogues and subsequent corpus luteum lifespan in the presence of norgestomet in Holstein heifers

This study investigated the effect of GnRH analogues on inducing ovulation of dominant follicle (DF) and subsequent corpus luteum (CL) lifespan in the presence of norgestomet implant in Holstein heifers. On day 6 to 8 of the estrous cycle (day 0 of the experiment), all heifers (n=15) received norgestomet implant followed by prostaglandin injection on days 0 and 1. On day 4, group 1 (n=4) and 2 (n=4) heifers received 12.5 and 25 μg Alarelin, respectively. Heifers in group 3 (n=3) received 10 μg Buserelin. Heifers in control group (n=4) did not receive any further treatment. Norgestomet was removed on day 8 in the treatment group and kept throughout the experiment in control group. From day 0, blood sampling and ultrasonography were performed. Heifers were monitored after inducing ovulation for 2 consecutive estrous cycles. DF ovulated within 33 h after GnRH injection. Progesterone started to rise on day 3 and declined on day 7.45 ± 0.28 after GnRH injection. Heifers in treatment groups displayed estrus 7.73 ± 0.24 days after GnRH injection followed by spontaneous ovulation. The lifespan of CLs were 5.36 ± 0.28 and 16.9 ± 0.37 days after inducing ovulation of DF in the presence of norgestomet and following spontaneous ovulation, respectively (P<0.05). In conclusion, the half dose of Alarelin induced ovulation of DF and the presence of single norgestomet implant after ovulation may be associated with short luteal lifespan.