230 SUPEROVULATORY RESPONSE OF BEEF COWS WITH OR WITHOUT A CORPUS LUTEUM AT THE TIME OF INSERTION OF A PROGESTERONE RELEASING DEVICE

Commercial embryo transfer programs require frequent superovulation of embryo donors. Although early reports suggested that donor cows require 60 to 90 days to recover from superovulation, recent information suggests that this interval could be reduced to 25 to 30 days. Because donor cows reovulate at variable intervals after embryo collection, some donors do not have an ultrasonically detectable corpus luteum (CL) when frequent superovulation programs are initiated. A retrospective study was performed to evaluate the influence of the presence of a CL at the time of initiating treatments on superovulatory response of beef donors that had been previously collected once and then were collected every 28 to 35 days 2 or 3 times. The data were from 190 collections performed in 48 Angus, 36 in 10 Brangus and 74 in 20 Bonsmara donors. On Day 0, all cows were ultrasonically examined for the presence of a CL (Falco 100 Vet, 8-MHz transducer, Pie Medical, the Netherlands) and were treated with 5 mg of oestradiol-17β and 50 mg of progesterone IM and a progesterone-releasing intravaginal device (Cue-Mate, Bioniche Animal Health, Belleville, Ontario, Canada). On Day 4, donors were superstimulated with Folltropin-V (Bioniche Animal Health), in twice-daily injections over 4 days or diluted in 20 mg mL–1 hyaluronan and given by a single IM injection. Folltropin-V dosages used were 300 or 400 mg (Angus), 260 or 300 mg (Brangus), or 200 or 300 mg (Bonsmara). On Day 6, all cows received 2 doses of PGF2α 12 h apart and Cue-Mates were removed in the p.m. In the a.m. of Day 8, cows received 12.5 mg pLH (Lutropin-V; Bioniche Animal Health) and were inseminated 12 and 24 h later. Ova/embryos were collected nonsurgically on Day 15 and evaluated following IETS guidelines. For each breed, superovulatory response (i.e. mean number of CL) and embryo data were evaluated by ANOVA for mixed models, using CL, FSH dose and treatment as fixed variables and cow identification as a random variable. Forty-six (24.2%) Angus donors, 4 (11.1%) Brangus donors and 5 (6.8%) Bonsmara donors did not have a CL at the time of initiating FSH treatment. There was no significant effect of FSH dose or treatment protocol on superovulatory response and the presence or absence of a CL did not influenced embryo production (P > 0.31). Mean (± SEM) number of CL, ova/embryos and transferable embryos were 13.2 ± 0.5, 12.4 ± 0.7 and 6.1 ± 0.4 in Angus donors with a CL vs 13.0 ± 0.7, 11.5 ± 0.9 and 5.6 ± 0.7 for those without a CL (P > 0.37); 14.8 ± 1.2, 14.2 ± 1.6 and 8.4 ± 1.1 for Brangus donors with a CL vs 15.2 ± 3.1; 11.2 ± 3.3 and 5.7 ± 2.8 for those without a CL (P > 0.34); and 13.2 ± 0.8, 11.2 ± 1.0 and 7.4 ± 0.5 for Bonsmara donors with a CL vs 17.4 ± 3.7, 13.6 ± 6.5 and 9.2 ± 4.3 for those without a CL (P > 0.16). In summary, the presence or absence of a CL did not affect embryo production in donor cows superstimulated every 28 to 35 days using a progesterone-releasing device and FSH. Study was supported by Bioniche Animal Health, Belleville, Ontario, Canada.