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Restoration of Normal Lactation in Hypothyroid Cows

Department of Animal Science, University of Tennessee, Knoxville 37901
and UT-AEC Agricultural Research Laboratory, Oak Ridge 37830¹

ABSTRACT

Seven dairy heifers treated with ¹³¹I to damage thyroid glands before first gestation were compared with their normal identical twins. Thyroid secretion rates and protein-bound iodine of treated cows averaged 33 and 38% of normal in the first lactation. Complete first lactations of the former were 50.6% of normal. Second lactations started at 55% of normal. Thyroxine feeding (8 g/day Prota-mone), started at 6 to 8 weeks of the second lactation, stimulated milk yields to 70% of normal for 9 weeks, after which they declined gradually to about 50%. Thyroxine feeding was continued through the dry period and next lactation in five paired lactations, which averaged 3,868 kg for the treated group and 3,737 kg for controls. Stopping thyroxine before the next calving resulted in a decrease to 23.5% of normal lactation. Thyroid deficiency must be corrected before the beginning of lactation to produce normal milk yields.

¹ Operated by the Tennessee Agricultural Experiment Station under Contract AT-40-1-GEN-242.