Exogenous melatonin after a treatment of artificial long days is able to increase LH secretion during seasonal anoestrus in Payoya goats

Abstract

One experiment was conducted to determine whether the treatment with artificial long days and exogenous melatonin can increase, by itself, luteinizing hormone (LH) secretion during spring (seasonal anoestrus) in Payoya goats and whether this treatment causes a variation in the reactivation of the LH secretion in the normal breeding season. The experiment started on 4 November and finished on 27 October. A total of 22 ovariectomised-oestradiol treated goats were used. Ten goats were exposed to long days (16 h of light/day) from 14 November to 20 February. On 20 February, they received one s.c. melatonin implant and were exposed to natural photoperiodic changes in an open shed. The control group was located in another open shed with any treatment during the whole experiment. For both groups, plasma samples were obtained twice a week for LH assay. The photoperiodic treatment induced an earlier fall of the LH secretion. However, after the melatonin treatment, a clear increase of LH secretion during the natural seasonal anoestrus in the treated group was observed, and no difference in the onset of the LH secretion at the normal breeding season was observed. We can conclude that, in Payoya goats, the photoperiodic–melatonin treatment is by itself able to induce a clear LH increase during the seasonal anoestrus and does not modify the reactivation of the LH secretion at the normal breeding season.