The effect of a mixed-management system on the release of oxytocin, prolactin, and cortisol in ewes during suckling and machine milking

Abstract

-Milk yield and plasma oxytocin (OT), prolactin (PRL), and cortisol (CORT) during suckling and machine milking were measured in multiparous ewes subjected to a mixed management system of 3 sucklings and two daily milkings. Peak hormones were significantly increased and were similar during suckling and milking for PRL (181 vs. 163.3 ng·mL -1 ) and CORT (12.5 vs. 11.5 ng·mL -1 ). During the period of exclusive suckling, OT was always significantly released (90.3 pg . mL -1 ); however, during the period of mixed management, OT concentrations only increased during suckling compared to milking (91.7 vs. 13.1 pg·mL -1 ). The mean volume of milk obtained during suckling (632 mL) was significantly higher than during milking (255 mL). Thus, during a mixed management system, oxytocin and prolactin releases are not under similar central regulation. A mixed system, without OT release during milking, does not contribute to accelerate the conditioning of ewes for machine milking.

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

“…A similar kind of CORT profile has been reported following stress imposed by weaning. However, CORT levels generally return to normal values three or four days after weaning [7,8]. This type of adaptation was not observed in the present study because CORT levels of the Gir group remained high in response to milking throughout the experiment.…”

“…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].…”

“…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].…”

“…Obviously, this mixed management increases the labour of milkers and thus many farmers wean calves at birth and submit both Gir and Gir × Holstein cows to exclusive machine milking, except for a short colostral period during suckling, as is done with dairy Bos taurus cows [7,12,13]. Indeed, the immediate separation of the cow and calf overlooks the fact that weaning inhibits OT and PRL release [8], and is accompanied by a significant decrease in milk production [7,8]. This contributes to the belief that Gir cows and their crossbred offspring can not adapt easily to machine milking.…”