Effect of bovine somatotropin on blood serum minerals, thyroid hormones and reproductive performance of lactating crossbred cows

Abstract

Apparently healthy multiparous lactating crossbred cows (24), on the basis of milk pmduction and parity were randomly allocated to 4 'treatment groups. These were control and 3 dose rates of 250 mg, 350 mg and 500 mg sometribove zinc suspension in a sustained release preparation. Cows in control group received placebo injections of normal saline. Treatments were initiated at 55 to 92 days postpartum and continued for 140 days. The injections were given subcutaneously on left or right side, at every 14 days for 10 injection cycles. Blood samples were collected on second day of sometribove injection. Blood samples were collected from all the cows in separate test-tubes, via jugular venipuncture during each injection cycle. Administration of bovine somatotropin did not affect the blood serum calcium, phosphorus, magnesium, sodium, potassium and chloride concentrations and remained within the normal range expected in lactating dairy cows. The serum triiodothyronine and thyroxine concentrations did not differ and remained almost similar in treated and control cows. The percentages' of cows remaining pregnant and calving rate were almost comparable in bovine somatotropin treated and control cows. Services per conception were lower in 250 and 500 mg groups when compared with controls, suggesting that services per conception were not affected due to bST treatment. Bovine somatotropin treatment had no discernible effect on gestation length.