Adult Finn-cross ewes, pregnant from September matings, were kept under natural photoperiod (control, 30 animals) or with an additional exposure to a 1 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 light-treated 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.