Effect of administration of recombinant bovine somatotropin on health and performance of lactating dairy cows diagnosed with hyperketonemia

The effect of administering recombinant bovine somatotropin (rbST) to cows with hyperketonemia during the early postpartum period on health, metabolic parameters, milk production, and early reproductive performance was evaluated in a double-blinded clinical trial. Cows from 8 dairy herds in New York State were tested weekly between 3 and 16 d in milk for elevated serum β-hydroxybutyrate. Cows were enrolled in the study when blood β-hydroxybutyrate was ≥1.3 mmol/L for the first time. Enrolled cows were randomly assigned to a treatment (n = 273) or placebo control (n = 270) group. Treated cows were given 325 mg of rbST subcutaneously on the day of enrollment and again 14 d later. Control cows received the same regimen except the syringe contained only the carrier without somatotropin. After enrollment, blood samples were collected weekly for 4 wk and submitted to the laboratory to be analyzed for selected metabolites. Risk ratios for clinical diseases subsequent to treatment were calculated using Poisson regression. Continuous data were analyzed using linear mixed models. Time to first insemination was assessed with survival analysis. In the 42 d following the first administration of rbST, incidence risks of displaced abomasum, clinical ketosis, metritis, clinical mastitis, and lameness were not different between treatment groups. Cows treated with rbST had a slightly lower body condition score 28 d after enrollment compared with control cows. In the 4 wk following enrollment, serum nonesterified fatty acids and aspartate amino-transferase were slightly higher for treated than control cows, respectively. Serum glucose, calcium, haptoglobin, and β-hydroxybutyrate were similar between groups. Treatment had no effect on resolution of hyperketonemia in any of the 4 wk after enrollment. Milk production in either of the 2-wk periods after each treatment was not different between treated and control cows. Furthermore, milk production was not different between groups from enrollment to 98 d in milk (42.6 ± 0.6 and 42.1 ± 0.7 kg/d for treatment and control groups, respectively). Treatment had no effect on time to first insemination (83 and 74 d in milk for treatment and control groups, respectively; hazard ratio = 0.72) or first insemination pregnancy risk (27 and 29% for treatment and control groups, respectively; risk ratio = 0.92). Based on the current results, it is not recommended to use a low dose of rbST as therapy for cows with hyperketonemia.