Ovarian activity and PRL plasma levels in ewes subjected to an artificial photoperiod followed by melatonin treatment
1992
Grasselli, F. | Tamanini, C. (Parma Univ. (Italy). Istituto di Fisiologia Veterinaria) | Prandi, A. (Udine Univ. (Italy))
This experiment was undertaken to study the effect of artificial extended light and exogenous melatonin on the onset of ovarian activity and PRL plasma levels in anestrous ewes. From March 19th, till April 23rd, twenty-two pluriparous ewes were exposed to an artificial photoperiod of 20 L: 4 D and then subjected to the natural photoperiod; beginning from April 24th, till the end of June, these animals were fed daily with 2.5 mg melatonin. Progesterone and PRL plasma concentrations were determined by validated radioimmunoassay on samples collected weekly from March 5th, till the end of June. The treatment was effective in advancing the resumption of ovarian activity (P0.05): by the end of June the percentage of cyclic ewes was higher in treated than in control animals (63 vs 40%); the artificial photoperiod did not induce any variation of PRL plasma concentrations, while melatonin was effective in dramatically and significantly (P0.01) reducing PRL plasma levels. Our results confirm the effectiveness of melatonin in advancing the breeding season in anestrous ewes and an inhibitory role of melatonin on PRL secretion
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