Control of seasonal reproduction in sheep and goats by light and hormones

Seasonal variations of reproductive ability have been demonstrated in male and female sheep and goats. For the female, there is a distinct breeding season. Whilst there are large breed differences in the duration of the sexual season, oestrous cycles generally start when daylength is decreasing and end when daylength is increasing. In some breeds, ovulation without oestrus occurs during the non-breeding season. Although males are able to mate all the year round, seasonal variations occur in the weight of the testis and seminal vesicles and in the fructose concentration of the seminal vesicles. Sexual behaviour and semen characteristics also show seasonal variations.