The importance of increased levels of oxytocin induced by naloxone to milk removal in dairy cows

The aim of this study was to test whether a more pronounced oxytocin release induced by naloxone during milking causes higher efficiency of milk removal. Eight pregnant multiparous Holstein cows from second to fifth lactation were used for this experiment. The experiment was carried out during three consecutive days, i.e. six milkings (three morning and three evening milkings). During first and third evening milking in cross over design (four and four animals) 250 mg of naloxone or 10 ml saline was injected 5 min before the start of udder preparation. During these milkings 2 IU of oxytocin was injected i.v. after stripping and the amount of milk obtained in response to oxytocin injection was measured. Pre-milking naloxone treatment increased the milking-related release of oxytocin, however, only in six of eight cows. The stimulatory effect of naloxone on oxytocin release in the mentioned six cows differed individually from 4 ng/l to 132 ng/l. Naloxone treatment did not influence milk yield before stripping and stripping milk yield. However, naloxone treatment significantly reduced the amount of milk obtained in response to oxytocin injection. Peak flow rate tended to be higher after naloxone treatment. In conclusion, oxytocin release seems to be very important for the evaluation of different milking routines and milk removal environment with respect to the welfare of dairy cows.