Influence of concentration, duration and route of administration of melatonin on reproductive performance of spring-mated polypay and polypay-cross ewes

The effects of exogenous melatonin on reproductive performance of 737 Polypay and Polypay-cross ewes were evaluated during a late March and April breeding period. Different concentrations (2 or 10 mg) routes of administration (fed vs implanted) and durations of administration (20 or 40 d before breeding) were studied. Estrus was synchronized in all ewes using 60 mg medroxyprogesterone acetate (MAP) in a vaginal pessary. Number of mature ewes lambing/ewe present at lambing was increased (P less than .05) nearly 20% by implanting for 40 d with melatonin (75%) or by feeding either 2 (72%) or 10 mg (73%) melatonin for 40 d before spring breeding compared with untreated control ewes (54%) or ewes implanted for only 20 d before breeding (58%). Date of lambing, number of lambs born/ewes lambing and number of lambs born alive/ewe lambing were not altered significantly by treatments. Number of yearling ewes (n = 166 for ewes 1.5 yr old at lambing time) lambing/ewe present at lambing was lower (P less than .01; 26%) than that of mature ewes (n = 381, greater than or equal to 2.0 yr; 68%). We concluded that feeding 2 or 10 mg melatonin or implanting melatonin for 40 d enhanced reproductive performance and effectively overcame the restrictions of seasonality of breeding in mature ewes. In yearling ewes, 10 mg melatonin increased the number of ewes lambing.     

Analysis of ovine peripheral blood lymphocyte subsets following Ficoll-Hypaque separation or erythrocyte lysis

Peripheral blood lymphocyte subsets were analysed with the aid of monoclonal antibodies and flow microfluorometry following separation by either the Ficoll-Hypaque method or erythrocyte lysis of the buffy coat. The percentage of lymphocytes labelled by the monoclonal antibodies SBU-T1, SBU-T4 and SBU-T8 were significantly greater (P less than 0.05) in samples obtained by erythrocyte lysis. In contrast, a lower percentage of lymphocytes was labelled by SBU-T6 following erythrocyte lysis (P less than 0.02). These data suggest caution when choosing a method for separation of peripheral blood lymphocytes.