Follicular recruitment and ovulatory response to FSH treatment initiated on Day 0 or Day 3 postovulation in goats

Abstract

The present study evaluates the effect of the presence of a large growing follicle at the onset of superovulatory treatment on follicular recruitment and ovulatory response in dairy goats. The treatment consisted of six equal doses of pFSH given every 12h (total dose: 200mg NIH-FSH-P1) which was initiated at Day 0 (Group D0) or Day 3 (Group D3) postovulation. Two half-doses of an analogue of prostaglandin F2α (delprostenate, 80μg each) were administered together with the last two FSH doses to ensure luteolysis. A dose of a GnRH analogue (busereline acetate, 10.5μg) was administered at the onset of estrus. Ovarian changes were evaluated twice a day by transrectal ultrasonography. Follicles were classified according to follicular diameter as small (3 to <4mm), medium (4 to <5mm) and large follicles (≥5mm). The number of corpora lutea (CL) was recorded after laparotomy performed 6 days after estrus. The work was conducted in replicates. In the first trial, the does were assigned to either the D0 (n=4) or D3 group (n=4) and in the second replicate, each goat was assigned to the alternate group. No large follicles were recorded and the diameter of the largest follicle was 3.3±0.1mm (mean±S.E.M.) at the initiation of the treatment in D0-treated goats. In contrast, a growing large follicle was present (6.7±0.4mm, P<0.01) when the treatment was initiated in D3-treated goats. In these goats, the number of small follicles increased 24h after ovulation but then declined 48h later, temporally correlated with the growth of the largest follicle of the first follicular wave. The number of small follicles recruited by the FSH treatment was significantly higher and occurred earlier in D0- than in D3-treated goats (9.0±1.3 versus 5.6±1.1 follicles; P<0.05; and 24h versus 48h from the onset of the treatment, respectively). The number of large follicles at the onset of estrus was higher in D0- than in D3-treated goats (14.4±1.9 versus 10.3±1.3; P<0.05). Consequently, the number of CL recorded 6 days after estrus were higher in D0- than in D3-treated goats (13.6±1.9 versus 10.4±1.9; P<0.05, respectively). These results demonstrate that the presence of a dominant follicle at the time of initiation of super-stimulatory treatment is detrimental to ovulatory response. This study supports the advantages of the so-called Day 0 protocol, e.g. treatment starting soon after ovulation, when the emergence of the first follicular wave takes place and there are no dominant follicles.