The Effect upon Milk Production and Body Weight of Varying Withdrawal Periods after Thyroactive Supplement Feeding

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Abstract
Withdrawal of 3 lb. of thyroactive feed supplement containing 15 g protamone daily from the ration of cows so fed for 10-14 weeks was compared over periods of 10, 15, 18, 25, and 30 days. Withdrawal in 10 days was accompanied by a sharp drop in milk yield and a temporary period of subnormal production. Less rapid decline was noted in the 15-, 18-, or 25-day withdrawal periods, with little difference in yield decline rates noted between the last 2 periods. Yields did not drop below estimated normal production after withdrawal periods of 15 days or more. Extending the withdrawal period to 30 days did not prevent a terminal drop from a partially stimulated yield to the estimated normal level. Rapid gains in body weight occurred after thyroactive feeding ceased. These were accompanied by increases in paunch girth large enough to account for nearly all of the weight increase as gastrointestinal fill. The total body water contents during and after treatment were essentially the same in control and treated groups, indicating very minor changes in water balance due to thyroactive feeding.