Melatonin advances june breeding and fall lambing in range and farm-flock type ewes

Influence of melatonin on reproductive performance was evaluated by randomly allotting Polypay-type ewes to four treatments: controls in drylot, melatonin-treated ewes in drylot, controls on range, and melatonin-treated ewes on range. An additional group of Targhees and Rambouillets was randomized by breed as control ewes or melatonin-treated ewes to test effect of melatonin in range ewes. All ewes were supplemented with 0.34 kg/head alfalfa-barley (1:1) pellets from 1600 to 1630 h daily, from April 15 to June 30. Ewes maintained on range received no further supplementation, while ewes in drylot received alfalfa pellets for maintenance. Melatonin was fed at 10 mg hd(-1) d(-1) in the pellet to designated ewes in drylot or on range. Three rams were put with each group of ewes on June 1 and rotated among groups at 7-d intervals during the first 30 d of breeding to reduce sire differences. After the first 30 d, ewe groups were combined with all rams. Melatonin induced (P<0.01) an earlier onset of estrus (approximately 17 d) as indicated by earlier lambing dates in Polypay-type, Rambouillet, and Targhee ewes managed on spring range. Melatonin also increased (P<0.01) the number of ewes that conceived during the first 30 d of breeding (June) for both management treatments (drylot and range) and for all breeds.