Alteration of seasonal reproductive patterns in mares following superior cervical ganglionectomy.

Oestrous behaviour, ovarian follicular development, ovulation and changes in hair coat were observed in Pony mares which were unoperated, sham-ganglionectomized control or bilaterally superior cervical ganglionectomized. Surgery was performed during the winter anoestrus (1975--1976). Reproductive patterns in all groups were similar during the first breeding season (1976) after operation but in ganglionectomized mares the onset of the next breeding season (date of first ovulation in 1977), the pattern of follicular development, date of first oestrus and pattern of hair coat changes were all significantly delayed relative to those of the non-operated and sham-operated mares in 1976 and 1977 and relative to their own patterns in 1976. These results indicate that the pineal-hypothalamo-pituitary axis may regulate or moderate annual reproductive rhythms in mares.