Circulating Levels of Melatonin following Its Oral Administration or Subcutaneous Injection in Sheep and Goats

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Abstract
The effect of differing doses and routes of administration of melatonin on plasma melatonin levels in sheep and goats was examined. Melatonin injected s.c. in a saline or oil vehicle caused high transitory peaks in plasma melatonin; oral administration, in either saline solution or adsorbed onto pelleted foodstuff, resulted in sustained elevated blood levels for periods exceeding 7 h. Oral dosages of .apprx. 2 mg were adequate to raise the normal daytime plasma levels in both sheep and goats to levels within the normal nighttime range. Apparently, with ruminants the oral route of administration provides a convenient and practical way of administering melatonin for physiological study.