Induction of milk ejection and milk removal in different production systems1

Abstract

Milk ejection is important during milking or suckling to obtain the alveolar milk fraction, which can represent more than 80% of the milk stored in the udder of dairy cows. In response to tactile teat stimulation, either manually or by the milking machine, milk ejection is induced by the release of oxytocin and resultant myoepithelial contraction. The time from the start of tactile stimulation until the occurrence of milk ejection spans 40 s to > 2 min and increases with a decreasing degree of udder filling. Therefore, cows need a longer prestimulation in the late stages of lactation or if the milking is performed shortly after the previous milking, whereas in full udders prestimulation is less important. Milk ejection is disturbed under several conditions, such as during milking in unfamiliar surroundings (i.e., a novel milking environment) or for several weeks immediately after parturition in primiparous cows. Disturbed milk ejection is due to a reduction of or absence of oxytocin release from the pituitary. The severity of disturbed milk ejection and the coping capacity toward a novel milking environment is related to cortisol release in response to ACTH (i.e., adrenal cortex activity). Therefore, susceptibility of individual cows to the inhibition of oxytocin release and milk ejection can be predicted by an ACTH challenge test. Comfortable surroundings, such as feeding in and lighting of the milking parlor, can increase the secretion of oxytocin. Overcoming the lack of oxytocin release by injection of exogenous oxytocin for an extended time results in a reduction of the mammary response to endogenous oxytocin. In different production systems, it has to be verified that udder stimulation is sufficient to prevent disturbed milk ejection. Different brands of automatic milking systems induce a sufficient prestimulation of the udder, even if a few minutes are needed for a successful onset of the teat clusters. Specific breeds used for less intense milk production may need the presence of their calves for sufficient oxytocin release during milking. In conclusion, in all milk production systems, the maximal possible reduction of stress has to be targeted and proper udder prestimulation must be performed for an optimal milking of the cow by the farmer.

Relationship between cortisol and acute phase protein concentrations in female rabbits

“…Such an increase could be related to the requirement for prolactin (in association with insulin and cortisol) for initiation of milk secretion in the periparturient period (Tucker, 2000). Moreover, frequent and intensive suckling play a role in maintaining lactation, primarily via stimulation of oxytocin release, but also provoking secretion of prolactin, vasopressin, ACTH and cortisol (Bruckmaier and Wellnitz, 2008;Olsson and Högberg, 2009). This is consistent with the observation of elevated cortisol concentrations in lactating primiparous females at early lactation (group 2) compared with nulliparous females (group 1) in the present study.…”

Effect of restricted suckling on milk yield, composition and flow, udder health, and postpartum anoestrus in grazing Holstein cows

“…It has been suggested that emotional stress may stimulate endogenous opioids release which in Table 3 Effect of suckling management on milk flow characteristics, udder health, BCS, and interval from calving to first postpartum ovulation of cows. turn may block oxytocin secretion and milk ejection (Bruckmaier and Wellnitz, 2008). Indeed, administration of the opioid morphine inhibited oxytocin release in dairy cows, while administration of an opioid antagonist restored normal secretion (Tanĉin et al, 2000), but how endogenous opioids mediate these effects is still unclear.…”

A comparison between the equine and bovine hypothalamus-pituitary-adrenocortical axis

“…However, no differences existed in cortisol response to an ACTH stimulation test between competition index categories (by dividing the number of times the cow displaced another at the feed bunk by the total number of displacements the cow was involved in, either as an actor or reactor) in Holstein dairy cattle [113]. Of interest, susceptibility of individual cows to the inhibition of oxytocin release and milk ejection can be predicted by an ACTH challenge test [114,115]. Cortisol concentrations did not differ in dairy cows between animals in social isolation compared with animals deprived of lying down both in the baseline series and after ACTH administration [116].…”