Resumen de Meta-analysis of the effects of sometribove zinc suspension on the production and health of lactating dairy cows
Objective—To provide an updated evaluation of the efficacy and safety of sometribove zinc suspension (rbST-Zn), a form of recombinant bovine somatotropin, in lactating dairy cows.
Design—Meta-analysis.
Sample—26 studies published in peer-reviewed journals or reviewed by a regulatory agency.
Procedures—To be included, a study had to involve the use of the rbST-Zn formulation available to US producers in accordance with the label instructions for treatment initiation (57 to 70 days postpartum), dose (500 mg, q 14 d), and route (SC).
Results—For cows treated with rbST-Zn, mean milk, 3.5% fat-corrected milk, fat, and protein yields were increased by 4.00, 4.04, 0.144, and 0.137 kg/d (8.8, 8.89, 0.32, and 0.30 lb/d), respectively; however, the concentration of milk components did not change. Pregnancy proportion for the first 2 breeding cycles was increased by 5.4%, and pregnancy proportion for the duration of the trial was reduced by 5.5% for rbST-Zn–treated cows, compared with proportions for untreated cows. Mean body condition score (1 to 5 scale) was reduced by 0.06 points during the period of rbST-Zn use for treated cows. Administration of rbST-Zn had no effect on milk somatic cell count, the number of days to pregnancy, or inseminations per pregnancy; rates of fetal loss, twins, cystic ovaries, clinical lameness, lameness lesions, or traumatic lesions of the integumentary system; and odds of clinical mastitis or culling.
Conclusions and Clinical Relevance—Results indicated that rbST-Zn administration to dairy cows effectively increases milk production with no adverse effects on cow health and well-being.
Recombinant bovine somatotropin is a production-enhancing technology that allows the dairy industry to produce milk more efficiently, which means that each liter of milk produced by cows treated with rbST requires fewer feed nutrients, results in less animal waste, and has a reduced carbon footprint, compared with each liter of milk produced by cows that are not treated with rbST.1 Sometribove zinc formulation is the only form of rbST commercially available in the United States. After a thorough review of well-controlled studies, the FDA concluded that rbST-Zn could be used safely and effectively on US dairy farms, and commercial use of rbST-Zn by US dairy producers began in 1994. Although some researchers2,3 suggested that commercial use of rbST would cause catastrophic health problems in dairy cows, the conclusions of investigators of numerous scientific reviews4–9 of the effect of rbST-Zn on the efficiency, health, and welfare of dairy cows were similar to those of the FDA.
In contrast to the conclusions reached by the FDA and investigators of those scientific reviews,4–9 an expert panel assembled by the CVMA concluded that health management practices on Canadian dairy farms were inadequate to address risks associated with rbST use.10 Formed at the request of Health Canada, the mandate for the CVMA expert panel was to determine whether the use of rbST in accordance with its label directions would increase milk production without resulting in serious health problems that could not be adequately controlled by cattle management practices implemented at that time.10 The CVMA expert panel's evaluation involved a series of meta-analyses of studies involving rbST administration to dairy cows. The results of those meta-analyses10 indicated that administration of rbST to dairy cows increases milk production; however, it also had a negative impact on cow health and welfare, especially in the areas of udder health, lameness, body energy, and lifespan.
The CVMA expert panel meta-analysis10 (CVMA meta-analysis) was subsequently published as 2 peer-reviewed articles,11,12 and results of those articles11,12 are often quoted when the animal health and welfare aspects of rbST are discussed. However, the FDA and other experts13 have expressed concerns about the findings of the CVMA meta-analysis because it evaluated data from studies that used different formulations of rbST with varying doses and dosing frequencies and in which rbST administration was initiated at varying times during the lactation cycle.
Since the publication of the CVMA meta-analysis,10–12 several large-scale studies14–19 have been conducted to investigate the effects of rbST-Zn on commercial dairy farms, and rbST-Zn has been administered to > 35 million US dairy cows, with few reports of adverse health effects.20 Results of those studies14–19 and anecdotal experiences on commercial dairy operations provide no evidence to support the serious risks to cow health predicted by the CVMA meta-analysis.10–12 Consequently, there was a perceived need for an updated evaluation of the safety and efficacy of rbST-Zn in lactating dairy cows, which led to the formation of another expert panel that consisted of a data manager and project coordinator, a professional statistician, and 6 domain (milk production and composition, udder health, reproduction, body condition, lameness, and culling) experts. The purpose of the study reported here was to describe the findings of that expert panel and provide dairy producers and veterinary practitioners with an updated review of the efficacy and safety of rbST-Zn. This evaluation was a meta-analysis of studies published in peer-reviewed scientific journals or reviewed by a regulatory agency in which rbST-Zn was administered to dairy cows in accordance with the FDA-approved label directions.
