Abstract
This study was conducted to investigate the effect of ovulation numbers on the progesterone and luteal volume in nonpregnant and pregnant Lori-Bakhtiari ewes. In the spring season 48 reproductive tracts of nonpregnant ewes (treatments included single ovulation, unilateral double ovulations, and bilateral double ovulations) and in the autumn season 144 reproductive tracts of nonpregnant and pregnant ewes (single ovulation, unilateral double ovulations, bilateral double ovulations, single ovulation with 1 foetus, single ovulation with 2 foetuses, unilateral double ovulations with 1 foetus, unilateral double ovulations with 2 foetuses, bilateral double ovulations with 1 foetus, bilateral double ovulations with 2 foetuses) were collected. The results indicated that the mean volume of the individual corpus luteum (CL) and the total volume of CL in the autumn season were significantly higher than the spring season. However, there were no significant differences in the progesterone concentration between unilateral and bilateral double ovulations. The results also indicated that in ewes with double ovulations and 1 foetus, the total volume of CL and the progesterone concentration were higher than those of the ewes with single ovulation and 1 or 2 foetuses. It was concluded that increasing the incidence of twinning rate does not appear to be a prerequisite for the presence of 2 CLs in the ewes.
Highlights
Changes in the volume and function of the corpus luteum (CL) secreting progesterone, which is responsible for the continuation of pregnancy in many species, are related to pregnancy with multiple foetuses [1,2]
The results showed that the mean volumes of individual CL and the total volumes of CLs during the autumn season were significantly higher (P < 0.05) than in spring season
The results showed that in nonpregnant ewes during the spring and autumn seasons, the serum progesterone concentration in single-ovulated ewes was significantly lower (P < 0.05) than the double-ovulated ewes
Summary
Changes in the volume and function of the corpus luteum (CL) secreting progesterone, which is responsible for the continuation of pregnancy in many species, are related to pregnancy with multiple foetuses [1,2]. The adequate secretion of progesterone has a significant effect on the achievement of a successful pregnancy and oestrous cycle regulation in females [3]. The vast majority of domesticated breeds of sheep show 1 or 2 ovulations in a single oestrus cycle [4]. Evidence shows that the highest ovulation rate occurs in the late summer and early autumn, the beginning of the natural breeding season, and decreases gradually in the late autumn and winter, which are out of breeding season for ewes [5]. Double ovulations are more common in sheep breeds and can lead to the desirable occurrence of twinning. It was found that the numbers of large follicles in ewes were 2–3 times more than the ovulation rate [6].
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