The effect of melatonin on the reproductive performance of three sheep breeds in Spain

In order to determine the efficacy of melatonin implants in initiating the lambing season and improving reproductive efficiency in sheep, ewes (n = 1932) from three breeds (Rasa Aragonesa, Assaf and Merino) received melatonin implants (Group M) every 45 days from the winter solstice (1 January and 15 February-winter; 1 April and 15 May-spring) on 12 commercial farms. The other group of ewes (n = 1715) served as control (Group C). Fertility (percentage of ewes lambed), litter size (number of lambs born per ewe lambed), and fecundity (number of lambs born per ewe in the group) were calculated. Rasa Aragonesa M ewes produced significantly more lambs than the C ewes on farms 3 and 4, after spring melatonin treatment: April (1.16 versus 0.83 lambs-fecundity; P < 0.01) and May (1.23 versus 0.97 lambs; P < 0.05) lambings, respectively. In the Assaf ewes, melatonin implants significantly improved fecundity on farms 5, 6 (winter): January (0.62 versus 0.42 lambs per ewe for M and C groups; P < 0.01) and February (0.64 versus 0.32 lambs; P < 0.01) lambings, respectively and on farm 8 (spring) for May (0.77 versus 0.54 lambs; P < 0.01). This improvement in fecundity is attributed exclusively to significantly higher fertility during these melatonin implantation periods. Concerning the Merino breed, the melatonin treatment increased fecundity only on farm 10, after winter treatment (February) (0.91 versus 0.61 lambs for M and C groups; P < 0.01). It can be concluded that melatonin could be a useful tool to improve lamb production in the three breeds under study, although its efficacy within each breed seems to vary according to the farm and season. (c) 2006 Elsevier B.V. All rights reserved.