Premilking stimulation effects on milking performance and oxytocin and prolactin release in cows.

For effects on milking performance, 12 Holstein cows were subjected to four stimulation routines: a) no stimulation, b) manual stimulation, c) manual stimulation with delayed milking, and d) intravenous infusion of .75 IU of oxytocin. In an added experiment, effects of the first two treatments on milking performance and release of oxytocin and prolactin 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 oxytocin and prolactin in sera at resting were 5.25 microU/ml and 16.5 ng/ml. Differences between mean peak concentrations of oxytocin (16.6 and 16.0 microU/ml) and prolactin (28.1 and 27.5 ng/ml) for stimulated and unstimulated cows were small. Mean oxytocin concentration in stimulated cows peaked at 2 min compared with 5 min for unstimulated cows. No difference in time of prolactin release was detected. The timing of oxytocin release, rather than maximal concentration, could be the most important factor affecting milking.