Factors affecting milk ejection and removal during milking and suckling of dairy cows

The release of oxytocin and milk ejection occurrence in response to teat stimulation are crucial for fast and complete milk removal during milking or suckling. The milk ejection reflex can be disturbed at central or peripheral level under different experimental and practical conditions. The central disturbance results in the lack or insufficient ejection of the alveolar milk into the cistern due to inhibited oxytocin release from pituitary into the blood circulation. The important role in the pathophysiological regulation of the inhibited release of oxytocin is played by an opioid system. Endogenous opioids have suppressive effects on oxytocin release under the normal conditions of milk removal. However under the conditions of disturbed milk ejection their role in dairy cows was not confirmed. Other possible mechanisms involved in the central inhibition of oxytocin release are discussed. In dairy cows as compared with rats the mechanisms involved in the regulation of oxytocin release at the central level remain unclear. The central inhibition of oxytocin release has often been observed in dairy practice during milking of primiparous cows after parturition, suckling by alien calf, calf removal before milking, milking of cows in the presence of own calf, relocation and milking in an unknown milking place. If sufficient released oxytocin cannot induce the transfer of milk from alveoli to cistern, peripheral mechanisms are involved. Peripheral mechanisms are related to the increased levels of catecholamines and/or activation sympathetic nervous system at the udder level. In conclusion, the release of oxytocin and milk ejection efficiency can be very easily suppressed by many factors. The effect of milking conditions on regulation of milk ejection has to be considered. Thus the physiological requirements of dairy cows have to be respected.