OVARIAN STEROIDS SECRETION, IN BEEF CROSSBREED EWES, AT DISTINCT MOMENTS OF YEAR, IN SÃO PAULO STATE

Abstract

To define possible seasonality reprodutive in ovarian steroidogenesis at latitude 22°53’S and longitude 46°29’W, evaluated oestradiol (E2) and progesterone (P4) plasma concentrations, during the estrus cycle, at seasons considerate reproductive and non breeding, adult ewes were induced and/or synchronized with progesterone intra-vaginal dispenser (CIDR®/13 days) and 500 IU of eCG (IM) injected upon device removal, at two periods throughout the year (experiment 1 – non breeding season, September and October; experiment 3 – breeding season, February and March), and natural estrus (experiment 2 – breeding season, January). In all experiments, blood samples were collected daily, in the morning, via jugular vein puncture during the estrous cycle to determine ovarian steroids plasma concentrations. The mean E2 (20.05 ± 11.12 pg/mL) and P4 (3.58 ± 2.38 ng/mL) concentrations evidenced differences between days of estrous cycle (p<0.0001), experiments (p<0.0001) and animals (p<0.0001). The mean oestradiol plasma levels have higher concentrations during synchronized estrus on September and October (non breeding season) than at the breeding season (February and March) or during the natural estrus period (January). These patterns of hormone concentrations revealed that follicular growth and development remained constant, compatible with ovulation, throughout reproductive cycle on different periods during either the synchronized or natural estrus. The mean progesterone plasma concentrations were higher during synchronized estrus at the breeding season, followed by the non breeding season, and lower during natural estrus period. In conclusion, normal steroidogenic function, follicular and luteal, was observed throughout the year, which revealed an ausence of seasonal influence within the related latitude, without anestrous season.

KEY WORDS: Oestradiol, progesterone, reproductive seasonality, sheep.