Melatonin and light treatment of ewes for autumn lambing

Forty spring lambing adult, and 24 unbred yearling, Suffolk crossbred ewes were allocated to 3 groups. Group I and II were maintained on 18L: 6D and Group III on Local light (51 degrees 42' N) during 24 Feb-13 April. During 13 April-11 July Group I changed to 9L: 15D and Groups II and III were group fed a diet containing melatonin and providing 3 mg/ewe at 16.00 hrs daily. A further 20 adult ewes, Group IV and V were maintained on Local light during 24 Feb-13 April; Group IV was transferred to 9L: 15D and Group V remained on Local light during 13 April-11 July. The ewes were exposed to vasectomised rams from the time of weaning on 3 June. All ewes were housed until 11 July and then remained at pasture thereafter. The performance of the yearling ewes was as follows - % Keel-marked during 11-28 follows: Group I - 90.0; Group II - 100.0: Group III 92.3; Group IV - 50.0; Group V - 10.0. There were no significant differences between Groups I, II and III. The following percentage of adult ewes lambed during 3-23 December - 66.7; 85.7; 69.2; 20.0 and 0.0 for Groups I - V respectively. Groups I, II and III were significantly higher than Group V. The performance of the yearling ewes was as follows - % keel-marked during 11-28 July: Group I - 100.0; Group II - 66.7; Group III - 22.2. The following percentage of yearling ewes lambed during 3-23 December - 50.0; 44.4 and 11.1 for Group I - III respectively. An assessment of these data in relation to autumn lambing is presented in the paper.