Effects of bovine follicular fluid and luteinizing-hormone-releasing hormone antagonist on the dominant follicle maintained by a norgestomet ear implant in heifers

Abstract

The effects of BFF and LHRHa on the dominant follicle, maintained by 9-d synthetic progestin (norgestomet) ear implants inserted at proestrus, were studied in cattle. From day 4 of implant insertion, heifers (n = 18) were injected twice daily with saline (control, n = 6) or charcoal-extracted bovine follicular fluid, 10 mL i.v. for 4 d (BFF, n = 6) or LHRHa, 0.8 mg i.v. for 3 d (LHRHa, n = 6). Follicular changes were monitored daily by ultrasonography. Plasma estradiol-17β, serum LH and FSH were measured by radioimmunoassays. The dominant follicle was maintained during the treatment period, and it ovulated after implant removal in control heifers. In BFF group, the dominant follicle either ovulated after implant removal (two of six heifers) or gradually regressed until day 10 in the post-implant period (other four of six heifers). In the LHRHa group, the dominant follicle regressed during or after the implant period in 5 of 6 heifers. The dominant follicle ovulated in 1 of 6 heifers. Growth rate of the dominant follicle, until it reached its maximum diameter, was lower in BFF group than the control group (0.4 ± 0.1 vs 0.7 ± 0.1 mm d−1; P < 0.01). Both BFF and LHRHa groups showed high regression rates in those follicles that did regress (2.2 ± 0.1 (n = 4) and 1.9 ± 0.8 mm d−1 (n = 5) respectively; P < 0.01), compared with no regression in the control group. The BFF injections failed to suppress serum FSH levels consistently in all the heifers treated. LHRHa-treated heifers showed a significant decline (P < 0.01) in the mean serum LH concentration. In conclusion, deprivation of LH causes atresia of the dominant follicle. Key words: Follicular fluid, LHRH antagonist, follicular dynamics, gonadotropins, estradiol-17β, ultrasound, regression