The effect of artificial light, hormones, and rams on the reproductive performance of Finn-cross ewes during the seasonal anoestrus in Israel

Abstract

SUMMARYAdult Finn-cross ewes, pregnant from September matings, were kept under natural (control) or artificial photoperiod (experimental). The artificial photoperiod consisted of an abrupt increase in daylength to 18 h for 30 days in November, followed by a step wise decrease of 30 min every 10 days until May.The ewes of the two groups were either exposed daily to rams after lambing in January-February or after weaning in March, or were kept isolated from the males until mating in April. Time of mating in the latter animals was determined by measuring the intra-vaginal electrical impedance. Hormone treatment for oestrus induction was given after weaning to a portion of the control and experimental ewes. The ovarian activity of the animals was determined by examining their plasma progesterone changes.Daily teasing of the ewes from lambing to weaning and/or treatment with artificially decreasing daylength did not influence the ovarian activity during this period. All the ewes which were examined for ovulation, from both the control and experimental groups, ovulated 40–60 days after lambing, and 96% of the animals of the two groups which were not treated with hormones for oestrus induction exhibited spontaneous oestrus in March–May.The lambing–first ovulation and the lambing–first spontaneous oestrus intervals were longer in the light-treated than in the control ewes, and in the animals kept isolated from the rams until mating than in those exposed to the males after lambing or weaning.A conception rate of 70–100% and a high rate of cycle activity were obtained during the two consecutive years of the experiment in both control and experimental animals, treated or not with hormones and exposed or not to rams. In view of these results, no conclusions could be drawn about the effectiveness of the artificial photoperiod, ram effect and hormone treatment, alone or in combination, in inducing cycling activity and to increase the fertility of Finn-cross ewes during the seasonal anoestrus in Israel.

The effect of a light pulse and melatonin, alone or in combination, on the reproductive performance of Finn-cross ewes in spring in Israel

“…In the present study the mean intervals from lambing to first ovulation and oestrus were longer, although not always significantly, in the light-treated than in the control ewes. A similar delaying effect on the appearance of sexual activity after February lambing of Finn-cross ewes was reported under artificially decreasing daylight from an initial daylength of 18 h (Amir & Gacitua, 1985).…”

“…All the ewes of the present work ovulated and the majority of them came into oestrus after lambing. The mean intervals from lambing to first ovulation and oestrus were very similar to those found in ewes of the same breed after October lambing (Amir, Rosenberg & Schindler, 1984), but shorter than the intervals reported after January lambing (Amir & Gacitua, 1985), and do not conform with the absence of oestrous ewes and the occurrence of occasional ovulations only, during this period of the year (Amir et al 1984). It appears, therefore, that in the present study the ewes did not enter seasonal anoestrus after lambing in January-February.…”