The effect on the health of lactating cows of treatment with galactopoietic doses of thyroxine or iodinated casein

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Abstract
1. The effect on cow health of galactopoietic stimulation with thyroactive materials was determined from a statistical study of the results of a large field experiment involving 2000 cows over a 3-year period.2. The same experimental procedure was followed on thirty-seven farms scattered over England, Scotland and Wales. This procedure was planned to ensure that half the cows in each herd would receive a course of treatment with iodinated casein or thyroxine, and that the other half would constitute a suitable set of controls. Cows that remained in the herds received second and third treatments in successive lactations.3. The galactopoietic stimulation was started at a fixed interval after calving, irrespective of the season of the year.4. The use of the thyroactive materials in successive lactations did not have any serious adverse effects on the health of cows. The effect on productivity was less than had been expected, since the increase in milk yield resulting during the period of hormonal treatment was often largely or completely negatived by a shortening of the lactation period.5. The incidence of disease was somewhat greater in the treated than the control group, the principal contribution to this difference being from the diseases described as digestive disorders. There were some other differences of lesser significance.6. The rate of disposal of treated and control groups was almost identical.7. There were no adverse effects on the reproductive life of treated cows; factors studied were the efficiency of coitus, interval between parturitions, length of gestation and incidence of abnormalities at parturition.