Effect of Chlorpromazine on the Performance of Lactating Dairy Cows

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Abstract
Studies were conducted to determine the oral dosage of chlorpromazine required to produce tranquilization in lactating Holstein cows and to evaluate the effects of feeding low levels of the tranquilizer on milk production during a 24-wk. period. In a series of trials involving 6 cows, no tranquilization was observed when as much as 5 g of chlorpromazine per day was divided into 2 equal portions and fed with the grain ration at morning and evening feedings. On the other hand, 2 cows showed a marked degree of tranquility after receiving single doses of 4.5 and 9.0 g of the tranquilizer, respectively. Thus, approximately 5 mg of chlorpromazine per pound of body weight was effective in producing tranquilization in the cows used. No chlorpromazine was detected in milk from cows at any level of administration. Twenty-four additional cows were used to evaluate the effects of feeding 3 different levels of chlorpromazine, i.e., 0, 250, and 500 mg per day, on milk production under different enviornmental conditions. No appreciable differences were observed among treatment groups with respect to milk production or body weight changes during the 24-wk. experiment. Total production of 4% fat-corrected milk for the 3 respective groups was 4524, 4752, and 4244 lb. per cow for the 24-wk. period.