Effects of Oxytocin Administered During the Dry Period on the Succeeding Lactation

The possible role of oxytocin released at milking time in causing depressed lactation of cows lacking dry periods was investigated with 14 cows paired on the basis of lactation potential.Milking of all cows ceased at an average of 60 days prepartum.One of each pair was administered twice daily intravenous injections of 5 IU oxytocin throughout the dry period.Oxytocin treatment produced milk let-down and delayed the usual regression of udder size observed in dry cows.After parturition, milk yields of most of the treated cows were below those of their pair nmtes.The average 22-week production was 2,869 kg for the treated cows and 3,573 kg for the controls, a statistically significant difference (P < .01).The depression in lactation was similar to that which has been caused by short dry periods.Oxytocin treatment without milking simulated the effects of continued milking until near parturition.