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

Abstract

The influence of Buserelin injection and Deslorelin (a GnRH analogue) implants administered on Day 5 of the estrous cycle on plasma concentrations of LH and progesterone (P 4), accessory CL formation, and follicle and CL dynamics was examined in nonlactating Holstein cows. On Day 5 (Day 1=ovulation) following a synchronized estrus, 24 cows were assigned randomly (n=4 per group) to receive 2 mL saline, im (control), 8 μg, im Buserelin or a subcutaneous Deslorelin (DES) implant in concentrations of 75 μg, 150 μg, 700 μg or 2100 μg. Blood samples were collected (for LH assay) at 30-min intervals for 2 h before and 12 h after GnRH-treatment from cows assigned to Buserelin, DES-700 μg and DES-2100 μg 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 until a spontaneous ovulation before Day 45. A greater release of LH occurred in response to Deslorelin implants than to Buserelin injection (P<0.01). Basal levels of LH between 12 and 48 h were higher in DES-700 μg group than in DES-2100 μg and Buserelin (P<0.05). The first wave dominant follicle ovulated 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 μg group. All GnRH treatments elevated plasma P 4 concentrations, and the highest P 4 responses were observed in the DES-700 μg and DES-2100 μg groups. The second follicular wave emerged earlier in GnRH-treated than in control cows (9.9 vs 12.8 d; P<0.01). However, emergence of the third dominant follicle was delayed in cows of DES-2100 μg treatment (37.0 d) compared with DES-700 μg (22.2 d), Buserelin (17.8 d) or control (19.0 d). In conclusion, Deslorelin implants of 700 μg increased plasma P 4 and LH concentrations and slightly delayed the emergence of the third dominant follicle. On the contrary, Deslorelin implants of 2100 μg drastically altered the P 4 profiles and follicle dynamics.