Premilking Stimulation Effects on Milking Performance and Oxytocin and Prolactin Release in Cows

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Abstract
For effects on milking performance, 12 Holstein cows were subjected to 4 stimulation routines: no stimulation, manual stimulation, manual stimulation with delayed milking and i.v. infusion of 0.75 IU of oxytocin [OT]. In an added experiment, effects of the first 2 treatments on milking performance and release of OT and prolactin [PRL] were measured. Milk yield, fat and protein content were not affected by any treatment. Machine-on times were shorter and peak and average milk flow rates higher for manually stimulated and OT-infused cows. Concentrations of OT and PRL in sera at resting were 5.25 .mu.U[units]/ml and 16.5 ng/ml. Differences between mean peak concentrations of OT (16.6 and 16.0 .mu.U/ml) and PRL (28.1 and 27.5 ng/ml) for stimulated and unstimulated cows were small. Mean OT concentration in stimulated cows peaked at 2 min compared with 5 min for unstimulated cows. No difference in time of PRL release was detected. The timing of OT release, rather than maximal concentration, could be the most important factor affecting milking.