Follicular dynamics and dominance in Booroola x Finnish Landrace and Booroola x Suffolk ewes heterozygous for the F gene

Abstract

Summary. To Group 3, the proportion of marked follicles that ovulated was higher for S ewes than in those of the prolific genotypes. The number of follicles not marked at Day 0 but ovulating (compared to the total number of ovulations) was higher in BFL, BS and FL (8/11, 9/13 and 9/13) than S (3/10) ewes. In Exp. 2, prolific (BFL + BS) and non-prolific (S) ewes were compared following destruction of follicles \m=ge\3mmwith the F1 left intact (Treatment 1) or destroyed (Treatment 2), 12 days after sponge insertion. At 4 days after treatment (at sponge removal), the numbers of 3\p=n-\4mm follicles were not different between the 2 treatments and a very high proportion of the F1 follicles left intact at Day 0 had regressed at Day 4 in both genotypes. From these results, it can be concluded that the higher ovulation rate in Booroola-crossed ewes is not associated with a higher number of recruitable follicles but involves late follicular-phase recruitment and selection combined with smaller preovulatory follicle diameters. Dominance by the largest follicle is not present in ewes of prolific or non-prolific genotypes. In contrast, it is likely that small sized follicles exert a negative effect on growth of large follicles.

Ultrasonographic study of ovarian follicular dynamics in ewes during the oestrous cycle

“…The growth of the ovulatory follicle was slower in the second period, which is similar to the observation in the study reported here of a static phase of growth in some but not all follicles. Follicle growth rates ranging from 0.9 mm day~x to 1.7mm day""1, have been observed in different breeds of sheep (Driancourt et al, 1986;Castonguay et al, 1990). Follicle regression rates observed in the study reported here appeared to be slightly lower than those in an earlier report (1.6 ± 0.6 mm day~1; Driancourt and Cahill, 1984) for follicles in a follicular phase induced by PGF2tl, with observations made at laparotomy.…”

“…The fact that dominance is weak or absent in sheep may be logical, since sheep are multiple ovulators and so more than one follicle should retain the potential to ovulate until late in the oestrous cycle. From a recent study (Castonguay et al, 1990), it was concluded that dominance by the largest follicle was not present in ewes of prolific genotypes; this was based on the finding that there was no difference in oestrus and ovulation rates between control ewes and ewes in which the largest follicle was destroyed, following withdrawal of progesterone-impregnated sponges.…”

Respostas endócrinas e ovarianas associadas com o folículo dominante da primeira onda folicular em ovelhas sincronizadas com CIDR ou PGF2alfa

“…grandes em ovelhas Suffolk, administrando respectivamente, CIDR + 750 UI de eCG ou 40 mg de FGA + 800 UI de eCG. Entretanto, uma pesquisa desenvolvida por Castonguay et al (1990) destacou que, possivelmente, um número significativo de folículos apresentando diâmetro de 1 -3 mm, pode induzir a atresia dos folículos grandes em fêmeas ovinas.…”

“…Quando da administração de P 4 exógena ou seus análogos (como o acetato de melengestrol-MAP) por 12 ou 14 dias, ocorreu a regressão do corpo lúteo, mas o estro e a ovulação apenas manifestaram-se quando a P 4 exógena foi removida (Castonguay et al, 1990). Os mesmos autores, utilizando esponjas impregnadas com MAP por 14 dias para sincronização de estro em ovelhas mestiças Boorola com Finnish (BFL), mestiças Boorola com Suffolk (BS), Finnish Landrace (FINN) e Suffolk (S) determinaram, por intermédio de laparotomia no dia da retirada do pessário, mudanças na população folicular.…”

Uso de protocolos reprodutivos em ovelhas da raça Santa Inês sobre a sincronização e tempo médio para aparecimento do estro, a taxa de prenhez na IATF e no repasse

“…(ROCHE et al, 1999). No período de administração da progesterona e seus análogos por 12 a 14 dias, ocorre a regressão do corpo lúteo, contudo o estro e a ovulação apenas manifestam-se quando a progesterona exógena for removida (CASTONGUAY et al, 1990). Estudos realizados em ovelhas demonstram que a principal atuação da progesterona ocorre no hipotálamo, decrescendo a freqüência dos pulsos de LH, e aumentando sua amplitude.…”