SUPEROVULATORY RESPONSE FOLLOWING ABLATION-INDUCED FOLLICULAR WAVE EMERGENCE AT RANDOM STAGES OF THE ESTROUS-CYCLE IN CATTLE

Based on the premise that superovulation in cattle is optimal when sup erstimulation is initiated at the time of follicular wave emergence, t he present study was done in beef heifers to determine if the superavu latory response following a single bolus of gonadotrophin treatment af ter follicle ablation (induced wave) at random stages of the oestrous cycle is comparable to the same gonadotrophin treatment at mid-dioestr us (spontaneous wave). In Experiment 1, heifers were assigned to nonab lation (n = 18) and ablation (n = 20) groups. In nonablated heifers, s uperstimulatory treatment was given as a single subcutaneous injection (Folltropin-V, 400 mg) at mid-dioestrus to coincide with emergence of the spontaneous follicular wave 8 to 12 days after oestrus. In ablate d heifers, the same superstimulatory treatment was given 1 day after a blation of all follicles greater than or equal to 5 mm at random stage s of the oestrous cycle to coincide with emergence of the ablation-ind uced wave. Tn both the nonablation and ablation groups, PGF(2 alpha) ( Estrumate, 500 mu g) was given 48 h after the superstimulatory treatme nt and artificial insemination was done 60 and 72 h later. Reproductiv e tracts were collected at the time of slaughter 6 or 7 days after ins emination. Observations made in Experiment 1, indicated that some abla ted heifers had only partial luteal regression at the time of insemina tion, while some others exhibited behavioral oestrus as early as 24 h after PGF(2 alpha) treatment. The design was amended in Experiment 2 t o address these problems. Heifers were assigned to nonablation (n = 17 ), ablation-alone (n = 20) or ablation plus progestogen (n = 20) group s. Follicle ablation, superstimulatory treatment, artificial inseminat ion and collection of reproductive tracts were done as in Experiment 1 . However, all heifers were given two doses of PGF(2 alpha) (500 mu g/ dose) 48 and 60 h after superstimulatory treatment to ensure complete luteal regression, and heifers in the ablation plus progestogen group received a norgestomet ear implant at the time of follicle ablation to prevent early ovulations. The implant was removed at the time of the second PGF(2 alpha) treatment. In Experiments 1 and 2, the means for t he ovarian and superovulatory responses were not significantly differe nt between groups. Averaged over the nonablation and all ablation grou ps for Experiments 1 and 2, the mean number of corpora lutea, fertiliz ed ova and transferable embryos were 22.9 Vg 18.6, 7.3 vs 7.8 and 5.4 vs 5.6, respectively. In summary, follicle ablation at random stages o f the oestrous cycle followed by a single bolus of gonadotrophin treat ment 1 day later resulted in a superovulatory response that was compar able to the same superstimulatory treatment administered around the ti me of spontaneous wave emergence at mid-dioestrus. The ablation/supers timulation method described herein offers the advantage of initiating superstimulatory treatment forthwith and assuring that treatment is co ncomitant with wave emergence to achieve an optimal superovulatory res ponse. Moreover, the full extent of the oestrous cycle is available fo r superstimulation and the need for detecting oestrus or ovulation and waiting 8 to 12 days to initiate treatment is eliminated. (C) 1997 El sevier Science B.V.