The effect of thyroxine on the metabolism of lactating cows. 1. General results and nitrogen metabolism

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Abstract
The effect of injecting 10 mg. thyroxine per day for 4 weeks into cows at 3 levels of food intake was investigated. The resultant increase in milk yield was accompanied by an increase in pulse rate, by loss of wt., by markedly negative N balance and by an increase in the excretion of water and creatine in the urine. The % fat in the milk was increased and small but statistically significant increases were observed in the % solids and N in the fat-free milk. Thyroxine appeared to stimulate lactation by increasing the cows'' cata-bolism, and this resulted in negative N balances. The negative N balances could be inhibited by increasing the intake of food.