Aetiology of disturbed milk ejection in parturient primiparous cows

Abstract

SUMMARY. Milk flow in nine primiparous cows with disturbed milk ejection (D) and in six corresponding control animals (C) with normal milk removal was recorded during machine milking and blood samples were taken before and during milking to determine plasma oxytocin, vasopressin, prolactin, cortisol, oestradiol-17/?, luteinizing hormone, progesterone and /?-endorphin concentrations. Manual teat stimulation before milking lasted for 1 min. After milk flow had stopped, air was blown into the vagina for 2 min. When milk flow had stopped again, 1 i.u. oxytocin and finally 10 i.u. oxytocin were injected to remove residual milk. During and after teat stimulation, oxytocin remained basal in D, but increased in C, whereas prolactin increased in both groups. While 94% of total milk was obtained in C during this period, only 9% could be removed from D, indicating lack of alveolar milk ejection. During vaginal stimulation, oxytocin increased transiently in D and more than by teat stimulation in C. This allowed the removal of 75% of milk in D, whereas almost no more milk was available in C. After oxytocin injections, 3 and 16% of residual milk were obtained in C and D respectively. Basal oestradiol-17/? concentration was higher in D than in C (11-6 and 2-0 ng/1 respectively), whereas /?-endorphin level was lower (24-1 and 86-6 /*g/l respectively). Basal concentration of luteinizing hormone and progesterone, and concentration of cortisol and vasopressin before and during milking were comparable in C and D. We conclude that in cows with disturbed milk ejection afferent nervous pathways to the hypothalamus were intact, because prolactin was released by teat stimulation. However, oxytocin was only released by vaginal stimulation, i.e. milk ejection was centrally inhibited during teat stimulation.

Milk yield, residual milk, oxytocin and cortisol release during machine milking in Gir, Gir × Holstein and Holstein cows

“…Additionally, all experimental groups produced milk at levels comparable with those described by other authors [7,20], and the Gir and GirHol groups did not exhibit a high percentage of residual milk as described for other zebu breeds [15] or for dairy cows submitted to different situations of stress [7,32] or during first milkings after parturition [6,16]. This confirms that CORT levels alone are often poor predictors of stress in lactating animals as reported by other research [33] and suggests that, if stress exists in Gir cows, it is not very acute and only concerns some animals in the group.…”

“…Moreover, some authors have reported that stress caused by first milkings following parturition or weaning is always accompanied by a lack of OT release and disturbed milk ejection [6][7][8], which was not recorded here.…”

“…Disturbance of milk ejection can be attributed to a selective inhibition of OT release from the hypophysis gland as described after weaning [8,16]; in this case, normal milk ejection can be established after OT administration [6]. Alternatively, it can be associated with milking stress and is characterised by high CORT and noradrenalin levels [16]; in this case, even OT administration did not restore complete milk ejection [6]. Recently, it was reported that Gir × Holstein cows exhibit a similar pattern of OT release during exclusive machine milking as during suckling/ milking management [11], which suggests that crossbred Gir × Holstein cows could be successfully submitted to exclusive machine milking.…”

“…Normally, machine milking provokes an oxytocin release and milk ejection via neuroendocrine reflex, but machine milking could sometimes cause stress and entail a significant reduction in milk yield [6][7][8]. As a result, some farmers allow crossbred cows to be suckled by their calves, because these cows produce more milk than those submitted to exclusive machine milkings [9][10][11].…”

Effect of rank, group size and number of group changes ante partum on the occurrence of milk ejection disorders in primiparous cows – a field study

“…Numerous studies were conducted to identify the physiological causes for MED (e.g. Kokorina 1956and 1959, Mielke & Brabandt 1963, Mielke 1992, Bruckmaier et al 1992, Kraetzl et al 1999and 2001a,b, Wellnitz et al 1999, Inderwies et al 2001, Macuhova et al 2002. However, the physiological interactions are not yet fully understood.…”