The effects of oxytocin and bovine somatotropin (BST) on production of cows milked once a day (OAD) were assessed in late lactation. Seventy four cows were milked OAD for 28 days including 7 days adaptation, 14 days treatment, and 7 days post-treatment. Treatments were OAD controls, OAD plus 5 i.u. oxytocin injected intravenously each day or OAD plus 20 mg BST injected subcutaneously each day. An additional 20 cows were milked twice a day (TAD) throughout the trial. Production of OAD cows averaged 11% less than that of the TAD controls during the first week of OAD milking. Milk yield was significantly increased by 13% in BST treated cows but was not affected by oytocin. Cessation of both treatments resulted in a reduction in yield compared to the OAD and TAD control groups. The failure of oxytocin to increase yield was not in agreement with previous results, possibly due to a lower dose rate of oxytocin in the present trial. Increased yields in BST treated cows suggested that udder capacity was not constraining yield and that BST may override the inhibition of milk secretion which occurs with extended milking intervals.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 153-158, 1991
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