The Influence of Oxytocin-Induced Udder Evacuation on Milk and Butterfat Production in a Complete Lactation

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Abstract
One set of identical twin cows, T63 and T64, was observed through 2 complete lacta-tions and the 1st 10 wks. of their 3d lactation. In the 1st lacta-tion both animals were milked as regular herd animals to ascertain the genetic potentiality in regard to production. T63 produced 183.3 lbs. of milk containing 4.68 lbs. fat and T64 produced 316.5 lbs. of milk and 9.35 lbs. of fat. In the 2d lactation T63 was again milked and managed as a regular herd animal while T64 was designated as the exptl. animal. The only deviation from regular barn procedures to which T64 was subjected was the oxytocin treat- ment. Following each normal milking 3 I.''U. of oxytocin were injd. intraven. and the animal was remilked to obtain the residual milk. T63 produced 1,071.0 lbs. of milk and 38-61 lbs. fat and T64 produced 6,054.3 lbs. of milk containing 214.7 lbs. fat. Thus, T64 produced 5.7 times as much milk and 5.6 times as much fat as T63. In the 3d lactation T63 received the oxytocin treatment and T64 was milked normally and was used as the control. The record for the 1st 10 wks. showed that the exptl. animal was out-producing the control in approx. the same manner as in the 2d lactation. The results indicate that the removal of residual milk greatly increased milk and butterfat production. The response of mammary gland to 1.5-30 I.U. of oxytocin per injection was also studied.