OVARIAN FOLLICULAR DEVELOPMENT AND ENDOCRINE RESPONSES IN FOLLICULAR-FLUID-TREATED AND HEMI-OVARIECTOMIZED HEIFERS

The effects of charcoal-extracted bovine follicular fluid (BFF) on end ocrine profiles and follicular development in intact and hemiovariecto mized postpubertal heifers were examined. Oestrus-synchronized heifers received Norgestomet implants on day 1 and 7 of treatment and were th en injected s.c. with 11 ml saline (control) or 11 ml BFF twice a day for 12 days. The ovary bearing the largest follicle (OV1) was removed on day 7 and the remaining ovary (OV2) was collected on day 13. Follic les were observed by daily ultrasonography and were classified accordi ng to diameter (size 1: 2-3 mm; size 2: 4-6 mm; size 3: 7-10 mm; size 4: > 10 mm). After ovariectomy they were classified by diameter and hi stologically as normal or atretic. Intact control heifers had increase d numbers of size 4 follicles on OV1 on days 6 and 7; no increase was observed in BFF-treated heifers (P < 0.03). In BFF-treated heifers, th e mean basal LH concentration was higher (P < 0.05) and that of FSH wa s lower (P < 0.04) than in controls. FSH concentrations in BFF-treated heifers decreased from 0.60 +/- 0.08 ng ml(-1) (day 1) to 0.22 +/- 0. 05 ng ml(-1) (day 7; P < 0.04). The concentration of oestradiol increa sed in control heifers, but not in BFF-treated heifers (P < 0.001). Af ter hemicastration, OV2 underwent compensatory hypertrophy in control heifers, with an increase in the number of size 2, 3 and 4 follicles ( P < 0.05), whereas BFF-treated heifers did not. Thus, total follicular volume was much lower in BFF-treated than in control heifers on day 1 3 (92.2 +/- 15.4 versus 1393.8 +/- 276.6 mm(3); P < 0.0002). A transie nt increase in FSH (P < 0.006) and oestradiol (P < 0.01) concentration s occurred after hemiovariectomy in control but not in BFF-treated ani mals. In control heifers, an analysis of temporal relationships showed negative correlations between the volume of size 3 and size 4 follicl es, and between FSH concentrations and the volume of size 3 and 4 foll icles. A positive correlation was found between the mean diameter of t he largest follicle and the concentration of oestradiol, whereas negat ive relationships were found between the concentrations of FSH and oes tradiol, and between FSH and the mean diameter of the largest follicle . Analysis of the histological data showed that the number and volume of follicles > 8.57 mm was lower in the BFF-treated OV1 ovary, whereas no differences were found for follicles less than or equal to 8.57 mm . An absence of or a lower number and volume of follicles greater than or equal to 3.68 mm was observed in BFF-treated OV2 compared with con trols. We showed that: (i) compensatory hypertrophy in the remaining o vary occurs in heifers when the ovary bearing the largest follicle is removed; (ii) treatment with BFF decreases the FSH concentration and f ollicular development in intact postpubertal heifers, and prevents com pensatory FSH increase and follicular growth after unilateral ovariect omy; and (iii) the histological population of follicles < 3.68 mm in d iameter are not altered following 12 days of BFF treatment. Our result s suggest that follicular development beyond 3-4 mm in cattle depends on an adequate circulating concentration of FSH.