Sensory and behavioural control of gonadotrophin 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 eminence. This inhibitory influence occurs only as a consequence of specifically defined behavioural interactions between the cow and calf in the presence of a maternal bond, cannot be simulated experimentally using thermal, electrical or mechanical stimuli, and is not dependent upon sensory ennervation within the udder. Indeed, the identity of the calf, either own or unrelated, appears to define the neuroendocrine events that attend the maintenance of the anovulatory state under controlled experimental conditions. Hence, new hypotheses that focus upon the 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 oxytocin, and modulation of synthetic or excitatory activity of GnRH secretory neurones. Defining the role of the special senses in transduction of signals from calves that influence these neuronal processes may provide insight for developing practical intervention strategies of the future.