Seasonal changes in ovulatory activity, plasma prolactin, and melatonin concentrations, in Mouflon (Ovis gmelini musimon) and Manchega (Ovis aries) ewes

Abstract

Seasonal changes in ovulatory activity, plasma prolactin and melatonin concentrations were monitored in a wild (Mouflon) and a domesticated (Manchega) breed of sheep, both originating and living under similar latitudes (40°N). Mouflons express ovarian cycles significantly later than Manchega ewes (October vs. July, P < 0.001); however, they ended cycling one month later than Manchegas (April vs. March, P < 0.05). While prolactin concentrations were high when Manchega ewes started to cycle, they were at their lowest concentrations when Mouflons started cycling. Overall, mean prolactin concentrations were higher (P < 0.001) in Mouflons than Manchegas throughout most of the year. Within the limits of sampling frequency, the duration of melatonin secretion was similar in both groups during the solstice and equinox periods; however, the amplitude was lower (P < 0.01) in Mouflons than Manchegas during the solstice periods. The significant breed differences in the seasonal hormonal changes may be attributed to a genetic influence in the endocrine responses to the same photoperiodic cues.