Lactation performance of Holstein cows treated with 2 formulations of recombinant bovine somatotropin in a large commercial dairy herd in Brazil.

Bovine growth hormone (bST) or somatotropin is a hormone in cattle that is responsible for growth regulation and milk production. Recombinant bST (rbST) is a synthetic derivation that has been developed to increase milk production efficiency in dairy cows and profitability in dairy herds. It increases milk yield immediately upon administration and also, milk yield is maintained at a higher persistency throughout lactation compared with cows not supplemented with rbST. In general, rbST increases milk production by 4 kg/cow per day over the course of the lactation and increases profitability. More than one commercial product has come on the market, but there are limited results for the more recent ones. Therefore, Dr J. P. G. de Morais and colleagues investigated, their results were published in the Journal of Dairy Science, Volume 100 of 2017, page 5945 to 5956. The title of their paper is:  Lactation performance of Holstein cows treated with 2 formulations of recombinant bovine somatotropin in a large commercial dairy herd in Brazil.

The objectives of the study were to compare the effects of two different rbST products on milk yield, milk composition (fat and protein), milk somatic cell count (SCC), and body condition score (BCS) in cows of a large commercial herd. Regulatory approved 500-mg zinc sesame oil base rbST (ZSO-rbST; Elanco Animal Health, Greenfield, IN) and vitamin E lecithin base rbST (VEL-rbST; LG Life Sciences, Seoul, South Korea) formulations were administered to 90 cows each per rbST group every 14 days over 17 injection cycles, starting at 57 to 70 days in milk. A Control group of cows received no rbST. 

Compared with Control cows, ZSO-rbST and VEL-rbST groups (combined) had increased milk yield and protein percentage, and lower BCS. For first-calf cows, the average milk yield was 37.8 kg per day for the ZSO-rbST treatment and 35.7 kg per day for the VEL-rbST treatment (difference 2.1 kg per day). For multi-lactation cows, the average milk yield was 40.1kg per day for the ZSO-rbST treatment and 38.8 kg per day for the VEL-rbST treatment (difference 1.3 kg per day). There were no differences in milk fat percentage between ZSO-rbST and VEL-rBST treatments, but milk protein content was greater with VEL-rbST treatment than with ZSO-rbST treatment. Nonetheless, cows treated with ZSO-rbST yielded more kilograms of fat and protein per day than cows treated with VEL-rbST. No significant differences in BCS were found between rbST treatment groups. The differential increase in milk yield between cows treated with ZSO-rbST and VEL-rbST was driven by the rbST response differences both within the 14-day cycle and throughout the 17 injection cycles. The cows treated with VEL-rbST demonstrated a more variable 14-day milk yield response curve, with more pronounced valleys between injections compared with the ZSO-rbST formulation. In addition, compared with Control cows only the ZSO-rbST treatment was effective in modifying lactation persistency. Compared with the VEL-rbST formulation, the ZSO-rbST formulation yielded more kilograms of milk, fat and protein with less variation throughout the seventeen 14-day lactation cycles for both first-calf and multi-lactation cows. The greater milk yield of the ZSO-rbST formulation over the VEL-rbST formulation was attributable to less variation within the 14-day cycles as well as a more consistent response throughout the 17 injection cycles.  

In conclusion, for dairy producers who have the choice of more than one rbST formulation, this study showed that the ZSO-rbST formulation performed better than the VEL-rbST formulation in increasing milk yield.