The influence of length day on melatonin and prolactin secretion during lactation in asesonal sheep

The study demonstrated that during the period of milking, the duration of the daylight had a significant effect on the lactation parameters in ewes lambed in January and June. Marked differences were noted in the levels of milk production in sheep, during the period of shortening daylight, i.e. in autumn, as the sheep lambed in June produced 50% less milk than ewes lambed in January. The dwindling milk production at the time of a shortening photoperiod resulted from the different course of melatonin and prolactin secretion. In the period of shortening daylight, the concentration of melatonin increased, while the secretion of prolactin decreased, thereby contributing to a lower milk synthesis.