Effect of Thyroprotein Feeding on Dairy Cows

Sixty-three cows fed no thyroprotein averaged 7,265 kg milk (308-day, mature equivalent compared to 7,237 kg averaged by 63 cows fed 10 g thyroprotein daily after 50 days postpartum. The maximum increase in milk production from thyroprotein feeding occurred during the first two weeks of feeding and amounted to a 7.0% increase over the control cows. From the 22nd to 42nd weeks of lactation milk production of thyroprotein-fed cows was less than that of controls. Milk fat tests were raised 0.41% (P < .10) for two weeks. Differences in lactation milk yield, fat test, and milk protein were not statistically significant. Fifteen cows fed thyroprotein from parturition averaged 6,516 kg milk (308-day, mature equivalent) compared to 6,703 kg for 18 control cows. Both control and thyroprotein-fed cows increased mature equivalent lactation yields for two or three successive years.