Inhibitory effect of continuous infusion of oxytocin on lactation in cows.

Sixteen Holstein cows in varying stages of lactation were randomly assigned to four groups of four cows each. Indwelling polyethylene catheters were placed in the jugular vein, and solutions were administered with infusion pumps. Group 1 (control) received 500 milliliters of saline solution (.9~ sodium chloride) per day. Group 2 received 50 United States Pharmacopeia Units (USPU) of oxytocin per day; group 3, 100 per day; and group 4, 200 per day during a 5-day treatment. During pretreatment and post-treatment of 4 days all cows were infused with 500 milliliters of saline solution. Oxytocin was diluted with saline solution to a concentration permitting amounts infused of 500 milliliters of solution per day. Yield of milk, fat, proteins, and total solids were determined daily. In the control group no differences between means of the three periods were significant; infusion of saline solution had no effect. Milk yields were lower during treatment and post-treatment than pre-treatment. Yields of protein and total solids during treatment were reduced compared to the pre-treatment. Fat yield was adversely affected by oxytocin treatments.