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

Abstract

Adult Finn-cross ewes, pregnant from September matings, were kept under natural photoperiod (control, 30 animals) or with an additional exposure to a I h long. 300 lux light pulse, 16-17 h after an artificial dawn (light-pulse treatment, 32 ewes) for 2-5 months. After lambing, the supplementary light was discontinued and half of the ewes from each group were injected daily with 2 mg melatonin for an additional 2-5 months.The light-pulse ewes produced heavier lambs and more milk, as can be deduced from the higher rate of growth of their lambs during the first 10 days of life, than the control animals. The light-pulse and/or melatonin treatments delayed the occurrence of the first post-partum ovulation and oestrus (which occurred in the untreated animals about 4 and 6 weeks, respectively, after lambing), by 1-3 weeks. However, more ewes exhibited oestrus and cyclic activity in the light-treated than in the other groups. The fertility in the lighttreated group was, consequently, superior to that in the group kept under natural photoperiod, in spite of the similar lambing rate of the mated ewes of the different groups.It is concluded that the light-pulse, but not the melatonin treatment, had a beneficial effect on the reproductive performance of the ewes, as measured by the weight of the newborn lambs, the milk production of the dams during the first 10 days post-partum, and the cyclic activity of the ewes after February lambing in Israel.opened the way to the administration of exogenous TNTK.ODUCTION melatonin to induce the stimulatory effect of short days. In order to increase the reproductive efficiency of T h e exposure of ewes to increasing daylength is sheep it is necessary, among other ways, to increase apparently necessary before the stimulatory effect of the lambing frequency of the ewes, i.e., to obtain s h o r t d a y s ( E n g i i s h el aL i 9 8 6 ) Karsch el al. (1986), fertile matings during the anoestrous season. Since however, stated that the 'reproductive onset' in the the photoperiod was identified as the cue to the e w e s w a s l i n k e d t o cessa tion of the long day signal annual reproductive cycle of the animals (Marshall, a n d d i d n o t r e q u j r e exposure to short-day cues. In 1932), many attempts have been made to induce t h e pre sent study the possibility of inducing cyclic cyclic activity in ewes during the sexually quiescent activity in ewes after February lambings was period by exposing them to artificial light changes examined by exposing the animals to a light pulse which mimic those of the natural photoperiod a n d/or melatonin administration. In view of preprevailing before and during the breeding season v i o u s r e p o r t s o n t h e p o s s i b | e act ion of the photo-(review: Hansen, 1985). This strategy, however, p e r i o d t o w h i c h t h e d a m s a r e exposed before and necessitates light-proof buildings, which are imprac-a f t e r partU rition on their milk production and on the tical under field conditions. The existence of a g r o w t h of the litter (Pet...