Impact of Single or Multiple Doses of Pregnant Mare Serum Gonadotropin (PMSG) on Superovulatory Response of Post-Partum Friesian Cows

Abstract

This study aimed to compare the effect of using PMSG at a level of 2500 IU in term of one dose, two doses (1250 IU for each at 12 h interval) or 4 doses (650 IU for each at 12 h interval) on superovulatory response (SOVR), and yield and quality of embryos. A total of 21 Friesian cows (450-550 kg LBW, 3.5-5.5 y old and 1-3 parities) were used as embryo donors. Cows were fed and managed under the same conditions. All cows were i.m. injected with 3 ml PGF2α/cow (Estrumate) for estrous synchronization. Cows in the 1st protocol (P1) were i.m. injected with one dose of PMSG (2500 IU/cow) on day 10 of estrous cycle (control), while those in the 2nd and 3rd protocols were i.m. injected with two doses of PMSG (1250 IU/dose/cow) at 12 h interval on day 10 of estrous cycle (P2) and with four doses of PMSG (625 IU/dose/cow) at 12 h interval on day 10 and 11 of estrous cycle (P3), respectively. After 48 hours of the last PMSG dose in all protocols, all cows were i.m. injected with 2 ml PGF2α/cow. Both AI and GnRH (5 ml Receptal/animal) injections were done on day 14 in P1 and P2 and day 15 in P3. Embryos were un-surgically flushed 7 days post-AI. Number of total follicles (TFN), large follicles (LFN) and CLs (CLN), and diameter of follicles/cow on day of AI and flushing were determined. Ovulation rate (OR), embryo recovery rate (ERR) and quality of non-surgically recovered 7 days post-AI were determined. Results showed that on day of AI, FN, LFN and follicular diameter tended to be the highest in P3, moderate in P2 and the lowest in P1. On day of flushing, total and large follicles were the greatest and the widest in P2, followed by P1, and the least and the narrowest in P3. Ovulatory sites (CLN) was greater in P1 and P3 (2.00 and 2.07/ovary) than in P2 (1.57/ovary). The effect of protocol, ovarian side and their interaction on follicular number and diameter, and CLs number was not significant on AI and flushing days. The response to CLs formation on day of flushing on the right, left or both ovaries was 100% in each protocol. Showing CLs was higher on the right than on the left ovaries in P1 (85.7 vs. 71.4%), being the opposite (71.4 vs. 85.7%) in P2 and similar in P3 (85.7 on each side). OR was higher (P<0.05) in P1 than in P2 (69.9 vs. 52.3%), but did not differ in P3 (59.1%) from that in P1 and P2. Percentage of cows produced embryos was highest in P3 (71.4%), moderate in P1 (57.1%) and the lowest in P2 (14.2%) with average number of 1.71, 1.86 and 0.57 embryos/cow, respectively. ERR was higher in P1 and P3 (46.5 and 41.3%) than in P2 (18.1%). About 25% of cows in P1 produced 5 embryos, and 40% in P3 produced 2 embryos versus one cow in P2 (14.3%) produced 4 embryos. Distribution of embryos at morula stage was higher (50%) in P2 than in P1 (30.8%) and P3 (33.4%). Distribution of embryos at compact morula stage was the highest in P1 and P3 (53.8 and 41.7%) than in P2 (25%) versus 15.4 and 16.6% at blastocyst stage in P1 and P3. Distribution of transferable embryos was 95.3, 50.0 and 83.3% in P1, P2 and P3, respectively. Superovulation of Friesian cows with PMSG (2500 IU/cow) on day 10 of the estrous cycle, in term of 4 doses (625 IU) at 12-h interval, showed the best follicular response (number and diameter) on day of AI and the higher ovulatory response, in term of number of un-ovulated follicles and CLs as well as percentage of cows responded to produce embryos (71.4%) on day of flushing. The same PMSG as a single dose showed the highest response, in term of number of transferable embryos/cow (1.71/cow).