The effects of conditioning to suckling, milking and of calf presence on the release of oxytocin in dairy cows

The aim of the study was to record the oxytocin (OT) release during milking (M) without or with calf presence, suckling (S) and finally calf removal j ust before the next milking in cows during postpartum or early lactation pe riods. Furthermore, the release of OT was examined during S and M in unknow n surroundings (parlour). A total of 20 Brown Swiss cows kept under loose h ousing environment were used in our experiment. In both periods, the cows w ere milked twice daily at 07.00 and 18.00 h and suckled three times daily a t 09.00, 14.00 and 20.00 h in the stall (tie housing). In the postpartum pe riod, 13 cows were suckled and milked in the presence of their calves in th e stall for the first 5 days of postpartum. Five from seven primiparous cow s were additionally suckled by their own calves in the parlour on day 5 at 20.00 h. On day 6, calves were separated and moved from mothers to the calf barn 10 min before morning M. After evening milking cows were relocated to the herd within the same stable and milked in the parlour for a period of 4 weeks without contact to their calf. For control, additional seven primip arous cows without calf presence (not suckled) were also milked in the tie housing. In the early lactation period, suckled cows were moved back to the tie housing 2 days before the start of two consecutive days of S by their own calves and milking. Afterwards, 10 min before M calves were separated a gain. Before S, two consecutive M were considered as controls. Results: The S stimulus during postpartum resulted in a higher OT release as compared w ith M in the calf presence and M after calf separation but not during M of not suckled cows. S in parlour reduced OT release. However, when not suckle d primiparous cows were first milked in parlour, OT release was more reduce d and in some cows total inhibition was observed. In early lactation during the first S, release of OT was lower than during control M, but, increased gradually with repeated S and reached a maximum already on the second day. After two S, during evening M, the M related OT release was reduced as com pared with controls. Calf removal 10 min before M reduced OT release as com pared with central M or M in calf presence. Tn conclusion, the calf presenc e and its removal can negatively influence OT secretion during M. Condition ing to machine milking caused a short-term reduction of OT release during f irst suckling, which normalised within 1 day. (C) 2001 Elsevier Science B.V . All rights reserved.