Effect of Melatonin on fertility, age and weight at puberty in sheep

Abstract

Puberty is the biological process that leads to a sexual mature state and its major feature is the acquisition of reproductive competence. Melatonin implants have been successfully used in adult ewes to forestall breeding season and also they have improved fertility and prolificacy. The aim of this work was to determine the influence of melatonin implants on weight, age and fertility on puberty. 141 Corriedale x Texel spring born ewe lambs were used. Date and weight at birth were registered, and animals were weighed every 15 days and also at first oestrus. Ewe lambs were randomly distributed in 3 groups: Group M (n=45) with melatonin subcutaneous implants and control groups S (n=48) injected with saline and C (n=48) without treatment. A fertility tested ram was used for oestrus detection. Heat was detected in 22.2%, 22.9% and 14.5% of lambs in each group respectively. A tendency in repeating oestrus after matting was observed for control groups. The percentage of ewe lambs showing oestrus was signiticantly lower than those reported by other authors and in our previous work. Group M lambs reached first oestrus with a higher weight (2Kg) than Group S, in spite of being 10 days younger. The first oestrus cycles showed abnormally long lenghts but turned to normal lenghts as breeding season advanced. Only 2 lambs, which belongs to Group S, were detected as pregnant by ultrasonographic diagnosis. It is concluded that melatonin do not modify age and weight at first oestrus, lenght if first oestrus cycles and fertility.