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Update on animal health concerns of recombinant bovine somatotropin (rbST): Meta-analysis of use in dairy cows
The commercial form of recombinant bovine somatotropin, sometribove zinc formulation (rbST-Zn), was approved by FDA as safe and has been successfully used by the U.S. dairy industry since 1994. However, a meta-analysis by an expert panel assembled at the request of Health Canada concluded that the commercial use of rbST would cause serious health and welfare problems. The present investigation utilized a series of meta-analyses to re-evaluate the efficiency and safety of rbST-Zn when used according to label. A total of 26 studies met the criteria which, were: 1) published in peer-reviewed journals or reviewed by regulatory agencies, 2) used the rbST-Zn formulation (Posilac) available to US producers, and 3) use was according to label for dose (biweekly), treatment initiation (57-70 d postpartum), and administration method (subcutaneous injection). Meta analysis results indicated that milk, fat, protein, and 3.5% fat-corrected milk yields were all increased (P < 0.001) by rbST-Zn ( average of 4.00, 0.144, 0.137, and 4.04 kg/d, respectively) whereas milk concentrations of fat, protein and lactose were unaltered (P < 0.09, 0.07, and 0.26, respectively). A 5.4% improvement in pregnancy proportion from rbST-Zn was detected for the first two breeding cycles after the voluntary wait period (P < 0.01). However, a 5.5% decrease (P < 0.05) in pregnancy proportion during the length of the trials was likely due to reduced estrous behavior. There was no effect of rbST-Zn on fetal loss, days open, services per conception, twinning, or cystic ovaries (P < 0.65, 0.96, 0.12, 0.68, and 0.43, respectively); on the odds of clinical mastitis or milk somatic cell count (P < 0.12 and 0.54, respectively); nor on rates of clinical lameness, lameness lesions, or traumatic lesions of the integumentary system (all P < 0.99). The rbST-Zn reduced body condition scores by 0.06 point (1 to 5 scale), a difference in body weight of about 3 kg (P < 0.03). No change to culling rate was associated with rbST-Zn (P < 0.63). Overall, the present meta-analysis demonstrates that rbST-Zn is effective and presents no unmanageable effects on health or welfare.
Keywords: bovine somatotropin, animal health, meta-analysis