by Amanda Smith, Associate Editor
Recombinant bovine somatotropin (rBST) has a long history of both use and disuse in the U.S. "Since commercial sales began in 1994, rBST has been given to approximately 35 million cows," noted Dale Bauman, Cornell University, at the American Dairy Science Association's annual meeting in Kansas City, Mo.
Yet, a 1998 meta-analysis conducted by the Canadian Veterinary Medical Association painted rBST in a negative light. The group found that, while its use improved milk yield and components, it resulted in adverse cow health effects.
In response to continued questions, Bauman, in conjunction with researchers from six universities, conducted another meta-analysis recently to re-evaluate the efficiency and safety of rBST when used according to label directions.
A total of 26 peer-reviewed studies with 14,000 cows were analyzed. Researchers found that the administration of rBST significantly improved milk yield by 9 pounds per cow per day. Fat, protein and 3.5 percent fat-corrected milk yields were also bolstered. Milkfat, protein and lactose concentrations were unaltered.
While the above results agreed with the CVMA's production-based conclusion, a much different result was seen in regards to health and welfare.
When comparing cows that received rBST to control cows, no significant differences were seen for somatic cell count or mastitis. While not significant, administration did reduce body condition scores by 0.06 point (equivalent to 7 pounds of body weight).
In terms of reproduction, there was a 5.4 percent improvement in pregnancy rate for rBST cows in the first two breeding cycles after the voluntary waiting period. Bauman did note, though, that there was a 5.5 percent reduction in pregnancy rate over the length of the trials, likely due to reduced estrous behavior. Between the groups, there were no differences in pregnancy loss, twinning or cystic ovaries.
Furthermore, no discrepancies were seen for clinical lameness, lameness lesions, traumatic lesions or culling between the two groups.
Differences from the CVMA study, Bauman noted, could be attributed to the additional studies conducted since 1998 and strict criteria requiring that all analyzed studies tested rBST under label directions only.
