The suckling interaction between a cow
and her calf is one of the factors that maintains
a cow in postpartum anestrus (the
period between calving and the beginning of
first estrous cycle). Anestrus continues if the
cow perceives that her calf is attempting to
nurse, even when the mammary glands have
been denervated or removed. Cross-fostering
of an alien calf to a cow fails to maintain
postpartum anestrus, indicating that cow-calf
recognition is also a factor. We restricted
calves so they could nuzzle the cow's head
and neck but could not suckle. Compared
with weaning calves 1 wk postpartum,
restriction lengthened the interval to first
postpartum ovulation but less than with
normal suckling. These results suggest that
maintaining cow-calf recognition in the absence
of the suckling stimulus is an essential
part of the nursing mechanism that prolongs
anovulation. Thus, blocking the cow's recognition
of her calf might further decrease the
postpartum interval to first ovulation.
