Effect of Thyroxine and Triiodothyronine on the Amount and Constituents of Milk in the Sarabi Dairy Cows Treated with Growth Hormone

The goal of this study was to determine whether thyroxine (T4) and triiodothyronine (T3) injections increase the amount and constituents of milk in the bovine growth hormone (bGH) treated dairy cows. Each group of 4 Sarabi received daily injections of either saline, 5μg T3/kg BW, 50μg T4, /kg BW, 25μg bGH/kg BW, 5μg T3/kg BW plus 25μg bGH/kg or 50μg T4/kg BW plus 25μg bGH/kg. Blood samples were collected every other day on day 7 till day 15. Plasma T3, T4 and bGH concentrations were measured by double-antibody RIA. Milk samples were daily collected from day 1 till day 20. Injections of T3, T4 and bGH significantly increased the plasma T3, T4 and bGH level and the amount of milk by 7%, 18% and 24% respectively. Injections of bGH plus T4 significantly increased the amount of milk 34%. Protein, fat and lactose concentrations of milk were not changed among all animals in the different groups. The results indicated that T4 increased the amount and constituents of milk in the bGH treated dairy cows.