Repeated administration of hCG on follicular and luteal characteristics and serum progesterone concentrations in eCG-superovulated does

Abstract

The objective of this study was to evaluate the effect of repeated administration of hCG on the follicular and luteal charactristics and serum progesterone concentrations in eCG-superovulated Merghoz does. The estrous cycles of 40 adult does were synchronized following a 12-day treatment with intravaginal sponges (Chronogest ®), with 1000 IU eCG injected 2 days prior to sponge removal. On the day of sponge removal (day 0), the females were randomly assigned to 4 treatments. The first group (h1; n = 10), received an i.m. hCG injection (500 IU; Pregnyl ®) on the day 0. The second group (h2; n = 10), received an i.m. hCG (500 IU) injection on days 0 and 1, while the third group (h3; n = 10) received i.m. hCG (500 IU) on days 0–2. Does in the control group ( n = 10) did not receive any hCG treatment. Blood samples were taken on days 0, 1, 2, 5 and 8 and analysed for serum progesterone (P4) concentrations. Premature luteal regression was considered to have occurred if the P4 concentrations declined to less than 1 ng/mL by day 8 following sponge removal. On day 8 goats were slaughtered and ovaries recovered for evaluation. In each case the CL's were counted and classified according to their appearance – as normal or as regressing. According to the serum P4 concentration on day 8, 42.8% (3/7), 0% (0/8), 0% (0/7) and 0% (0/6) of the goats underwent premature luteal regression in the control, h1, h2 and h3 groups, respectively. The control group was the only group in which there was a significant increase in the number of regressing CL's on day 8 (5.1 ± 1.5; P < 0.05). The characteristics of the CL's, including the mean diameter and weight was greater ( P < 0.05) in the h2 and h3 groups, compared to the control group (10.9 ± 0.7, 11.0 ± 0.9 vs. 7.9 ± 1.1 mm and 640.0 ± 101.4, 691.7 ± 111.7 vs. 294.3 ± 143.7 mg, respectively). No differences ( P < 0.05) in the number of large follicles present on the ovaries were recorded on day 8 between the groups. However, the diameter of the large follicles present on the ovaries on day 8 was greater ( P < 0.05) in goats in the h2 and the h3 groups, compared to the control (15.3 ± 0.6 and 12.9 ± 0.3 vs. 8.6 ± 1.7 mm, respectively; P < 0.05). The serum P4 concentrations were higher in the h2 and the h3 groups than in the control group on days 2 and 8. The serum P4 concentrations on day 8 also recorded a positive correlation with the normal CL's, CL diameter and CL weight ( P < 0.001). These results indicate that the repeated administration of hCG post-sponge removal presumably prevents premature luteal regression and improves luteal function in goats after eCG-superovulatory treatment. However, neither the number of persistent follicles nor the diameter of the persistent follicles was reduced.