Effects of Buserelin injection and Deslorelin (GnRH-agonist) implants on plasma progesterone, LH, accessory CL formation, follicle and corpus luteum dynamics in Holstein cows

The influence of Buserelin injection and Deslorelin (a GnRH analogue) impla nts administered on Day 5 of the estrous cycle on plasma concentrations of LH and progesterone (P-4), accessory CL formation, and follicle and CL dyna mics was examined in nonlactating Holstein cows. On Day 5 (Day 1=ovulation) following a synchronized estrus, 24 cows were assigned randomly (n=4 per g roup) to receive 2 mL saline, im (control), 8 mu g, im Buserelin or a subcu taneous Deslorelin (DES) implant in concentrations of 75 mu g, 150 mu g, 70 0 mu g or 2100 mu g. Blood samples were collected (for LH assay) at 30-min intervals for 2 h before and 12 h after GnRH-treatment from cows assigned t o Buserelin, DES-700 mu g and DES-2100 mu g treatments and thereafter at 4- h intervals for 48 h. Beginning 24 h after treatment, ovaries were examined by ultrasound at 2-h intervals until ovulation was confirmed. Thereafter, ultrasonography and blood sampling (for P-4 assay) was performed daily unti l a spontaneous ovulation before Day 45. A greater release of LH occurred i n response to Deslorelin implants than to Buserelin injection (P<0.01). Bas al levels of LH between 12 and 48 h were higher in DES-700 mu g group than in DES-2100 mu g and Buserelin (P<0.05). The first wave dominant follicle o vulated in all cows following GnRH treatment. Days to CL regression did not differ between treatments, but return to estrus was delayed (44.2 vs 27.2 d; P<0.01) in cows of DES-2100 mu g group. All GnRH treatments elevated pla sma P-4 concentrations, and the highest P-4 responses were observed in the DES-700 mu g and DES-2100 mu g groups. The second follicular wave emerged e arlier in GnRH-treated than in control cows (9.9 vs 12.8 d; P<0.01). Howeve r, emergence of the third dominant follicle was delayed in cows of DES-2100 mu g treatment (37.0 d) compared with DES-700 mu g (22.2 d), Buserelin (17 .8 d) or control (19.0 d). In conclusion, Deslorelin implants of 700 mu g i ncreased plasma P-4 and LH concentrations and slightly delayed the emergenc e of the third dominant follicle. On the contrary, Deslorelin implants of 2 100 mu g drastically altered the P-4 profiles and follicle dynamics. (C) 19 98 by Elsevier Science Inc.