Thyroprotein for Lactating Cows in Mid-Summer

Abstract

Summary Thyroprotein was fed in midsummer to four cows on a 15-wk. double reversal study at a rate of 1.5 g. per 100 lb. of body weight, and at levels of 1.33 g. and 2.0 g. to six cows on 8-wk. continuous study, using two controls. 1. F.C.M. production increases noted were 32 per cent on reversal and 12 and 22 per cent on continuous as compared to preliminary period with an 8 per cent loss for controls on the latter study. 2. Efficiencies of T.D.N. utilization, using formula table 1 were 69 per cent for thyroprotein feeding periods compared to 104 per cent on basal ration for reversal trial; and 71 and 69 per cent respectively for continuous study, with 99 per cent efficiency for control pair. 3. Several cows receiving thyroprotein improved in efficiency of T.D.N. utilization as the period of thyroprotein feeding proceeded. Rapid body weight losses occurred in both trials when thyroprotein was fed, even when additional T.D.N. was provided. When thyroprotein was withdrawn from the ration of two cows on continuous trial they suffered heavy losses in milk yield and made unusually rapid and efficient weight gains over a 21-day period during cooler weather. These rapid gains and losses raise questions concerning the type of tissue involved. 4. Accelerated respiratory rates and pulse rates, as well as increased body temperatures, offered partial explanation for the reduced efficiency of energy utilization by the thyroprotein-fed cows during this summer trial.