Superovulatory response of dairy cattle (Bos taurus) in a tropical environment

Dairy (Bos taurus) heifers and cows (n=40) in a tropical environment were treated during mid-luteal phase using either SUPER-OV(R) or OVAGEN to induce superovulatory response after synchronization of the superovulatory estrus with a synthetic progestagen and cloprostenol (PG). Estrous cattle were inseminated twice using frozen-thawed semen, and embryos were recovered nonsurgically, on-farm, 7 d later. Between initiation of gonadotrophin treatment and recovery of embryos, 4 blood samples per animal were collected from 26 animals for determination of plasma progesterone (P4) concentration. Two (5%), 28 (70%) and 10 (22%) of the animals were observed in estrus 1.5, 2 and 2.5 to 3 d after PG, respectively. There was no difference (P=0.7) in the number of palpable CL between animals treated with SUPER-OV(R) (7.6 +/- 1.0; n=18) and those treated with OVAGEN (7.9 +/- 1.1; n=22). There was also no significant difference (P>0.05) between Jersey vs Ayrshire breeds or heifers vs cows in the ovarian response as estimated by the number of palpable CL. However, a higher proportion of Ayrshire cattle and donors treated with OVAGEN yielded a higher total number and viable/transferable embryos than Jersey and SUPER-OV(R)-treated cattle. There was a significant (P<0.05) correlation between the number of CL and total number of embryos (r=0.65); the number of transferable embryos was also significantly related to the total number of embryos per recovery (r=0.85; P<0.05). For 15 animals with normal P4 profiles, the mean (+/- SEM) plasma P4 concentration was 14.4 +/- 0.8, 0.5 +/- 0.2, 5.4 +/- 1.1 and 39.4 +/- 3.0 nmol/L at initiation of gonadotrophin treatment, superovulatory estrus and Days 3 and 7, respectively. The mean (+/- SEM) interval between a PG injection given after embryo recovery and the induced estrus was 7.1 +/- 0.7 d (range 3 to 14 d) and the length of the superovulatory cycle was 24.1 +/- 3.2 d (range 12 to 35 d).