SENSORY AND BEHAVIORAL-CONTROL OF GONADOTROPIN-SECRETION DURING SUCKLING-MEDIATED ANOVULATION IN COWS

A major limiting factor in the resumption of postpartum ovarian cycles in cattle is the inhibitory influence of the suckling calf on central regulatory elements controlling the release of GnRH from the median e minence. This inhibitory influence occurs only as a consequence of spe cifically defined behavioural interactions between the cow and calf in the presence of a maternal bond, cannot be simulated experimentally u sing thermal, electrical or mechanical stimuli, and is not dependent u pon sensory ennervation within the udder. Indeed, the identity of the calf, either own or unrelated, appears to define the neuroendocrine ev ents that attend the maintenance of the anovulatory state under contro lled experimental conditions. Hence, new hypotheses that focus upon th e relationship between physiological correlates of maternal behaviour and hypothalamic regulation of LH secretion are currently being tested . Specific aspects of these relationships remain conjectural, but are postulated to include the regulation of opioid tone, intracerebral oxy tocin, and modulation of synthetic or excitatory activity of GnRH secr etory neurones. Defining the role of the special senses in transductio n of signals from calves that influence these neuronal processes may p rovide insight for developing practical intervention strategies of the future.