Melatonin levels in ewes and lambs under suckled and non-suckled regimens during the first eight weeks postpartum

Abstract

A study was conducted to establish a 24 h serum melatonin profile in neonatal lambs and to correlate this profile with the maternal 24 h profile. Twin female crossbred lambs were separated, at birth, into 2 groups (suckled vs. non-suckled, n = 5). Daytime and nocturnal blood samples were collected from ewes and lambs from birth through 8 weeks postpartum. Daytime serum melatonin levels were less (P < .002) than nocturnal levels in all ewes (n = 5) studied. Melatonin patterns were characterized by low day time (51.3 to 66.8 pg/ml) and high nocturnal (113.8 to 246.6 pg/ml) concentrations. Frequent blood collection revealed obvious fluctuations in melatonin within ewes suggesting that melatonin is released in a pulsatile pattern. Significant differences (P < .03) in day time melatonin levels were observed in 2 of the 5 pairs of lambs. Day time melatonin levels ranged from 0.0 to 91.61 pg/ml and 0.0 to 179.47 pg/ml for non-suckled and suckled lambs, respectively. Differences (P < .03) in nocturnal melatonin levels were observed in only 1 lamb pair. Nocturnal melatonin levels ranged from 0.0 to 115.41 pg/ml and 15.90 to 249.46 pg/ml for non-suckled and suckled lambs, respectively. Differences (P < .05) in day and night serum melatonin levels were seen in 7 of 10 lambs studied. Analysis of co-variance revealed no significant relationship between ewe and suckled lamb 24 h serum melatonin profiles. Data from this study demonstrate that detectable levels of melatonin are present in the neonatal lamb. It is also concluded that the endogenous melatonin rhythm of the ewe did not directly influence the postnatal melatonin rhythm of the suckled lamb, as evidenced by the similarity between suckled and non-suckled melatonin levels. The data further suggest that, in the adult, melatonin is released in a pulsatile manner.