The Effect of Feeding Thyroprotein to Dairy Cows during the Decline Of Lactation in Successive Lactations

Abstract

Summary Five cows were fed 15 g. thyroprotein daily during the declining phase of two successive lactations, and two other cows were fed thyroprotein in single lactations. Each of the cows fed thyroprotein was paired with a suitable control cow. Thyroprotein produced an increase in milk yield and heart rate and slight to insignificant changes in respiration, body temperature and milk fat test, as well as a loss of body weight. Body weight gains were resumed in 2 mo. following introduction of the thyroprotein and, at the same time, the average milk production and other physiological characteristics indicated that the treated cows again were functioning similarly to the controls. The histology of the thyroid gland of the treated cows indicated that it was almost inactive at this time. Following removal of thyroprotein when the cows were dried off, the cows continued to regain weight during 60-day dry periods and freshened apparently in normal condition. No harmful effect could be attributed to this moderate thyroprotein feeding either because of stimulation or of depression.