Effects of melatonin implants in ram lambs

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Abstract
Sixteen pinealectomized and 19 unoperated ewes were exposed to constant light for .apprx. 4 wk before and 4 wk after lambing; 6 ram lambs born to unoperated ewes were implanted s.c. with melatonin sachets while 8 ram lambs were implanted with empry sachets. The 8 ram lambs born to pinealectomized dams also received empty implants. Ewes and lambs were then returned to the field. Analysis of weekly blood samples indicated that prolactin secretion was significantly decreased in the ram lambs with empty implants between 44-51 wk of age; lambs treated with melatonin failed to show a significant change during development. All 3 groups of rams had elevated LH [luteinizing hormone] levels between 7 and 17 wk of age and a 2nd period of high LH between 27 and 40 wk. There were no significant differences between groups in the patterns of FSH secretion; FSH was highest between 7-17 wk of age, and again between 27-40 wk of age. Plasma testosterone levels in all groups increased gradually between 4 and 35 wk. Between 38 and 48 wk of age testosterone concentrations were markedly elevated in all groups. Growth was not affected by melatonin treatment. Neonatal melatonin treatment evidently has subtle endocrine effects; whether these effects are sufficient to compromise fertility in the ram remains to be established.