Comparative study of ovarian follicular dynamics and plasma concentrations of FSH and LH in lactating and non-lactating mares / Estudo comparativo da dinâmica folicular ovariana e concentrações plasmáticas de FSH e LH em éguas lactantes e não-lactantes

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The objective of the present study was to evaluate the folliculogenesis in lactating mares and to compare the follicular dynamics and the FSH (follicle stimulating hormone) and LH (luteinizing hormone) profiles of lactating and non-lactating mares. In addition, the effects of season and body condition, as well as changes in the uterine echotexture and corpus luteum diameter, were also evaluated. Lactating mares (n=24) were selected at the day of parturition. Non-lactating cyclic mares (n=15) were randomized and selected in replicate for each lactating mare. The ovaries and uterus were evaluated daily by ultrasonography. Weight and body condition score were recorded at the day of parturition on the Lactating Group and at the day of randomization on the Non-lactating Group, and weekly, afterwards for both groups. The follicular emergence occurred before or very close to the day of parturition in lactating mares that ovulated in the foal heat. The future dominant follicle, at the day of emergence, had a size advantage in diameter when compared to the second largest follicle. Moreover, during the puerperium and the first interovulatory interval, the two largest follicles from the ovulatory wave had similar growth rates between the day of emergence and deviation. The growth rates of the two largest follicles were not affected by the season. The intervals from emergence of the dominant follicle to deviation and to ovulation were not different between the Lactating and Non-Lactating Groups. The emergence of the ovulatory wave occurred under elevated and/or increasing concentrations of FSH in both groups of mares. During the puerperium, the follicular emergence and deviation occurred earlier, when compared to the non-lactating cyclic mares. The mechanism of "follicular selection" (deviation) in lactating mares seems to be similar to non-lactating mares, due to the similarity of the follicular diameters and plasma concentrations of FSH and LH around the time of deviation. The maximum diameter of the dominant follicle and its diameter at Day -1 were larger in the Lactating than in the Non-Lactating Group. Using a mathematical method was possible to identify greater number of minor waves in the Lactating Group. The peak of endometrial echotexture score occurred earlier in lactating mares when compared to the non-lactating mares. The luteolysis, apparently, did not differ between the two groups of mares. Longer intervals from parturition to the first ovulation were associated with lower body condition score at 22 days postpartum, greater weight loss and occurrence of parturition in the Spring. Four distinct reproductive statuses were characterized in the Lactating Group: a) Continuous reproductive cyclicity after parturition; b) Prolonged interval from parturition to ovulation; c) Postpartum ovulation followed by anestrous; and d) Postpartum anestrous. Therefore, the present study shows that the folliculogenesis in postpartum mares is influenced by the parturition, but it is very similar to the folliculogenesis of non-lactating mares, mainly after the time of follicle selection.

ASSUNTO(S)

Égua pós-parto mares follicular dynamics hormônios dinâmica folicular reproducao animal hormones

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