Abstract
The objectives of this controlled study were to compare the effects of 2 different formulations of recombinant bovine somatotropin (rbST) on milk yield, milk composition (fat and protein), milk somatic cell count, and body condition score (BCS) among dairy cattle in 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 per the manufacturers' recommendations every 14 d over 17 injection cycles starting at 57 to 70 d of lactation (90 cows per rbST group). Control cows (n = 60) received no rbST. Somatotropin-treated animals (VEL-rbST and ZSO-rbST combined) had increased average milk yield and protein percentage and lower average BCS compared with control cows. For primiparous cows, average milk yield was 37.75 kg/d with the ZSO-rbST treatment and 35.72 kg/d with the VEL-rbST treatment. For multiparous cows, average milk yield was 40.13 kg/d with the ZSO-rbST treatment and 38.81 kg/d with the VEL-rbST treatment. There were no differences in milk fat percentage between VEL-rbST and ZSO-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 both rbST treatment groups. The differential increase in milk yield between cows treated with ZSO-rbST and VEL-rbST was driven by rbST response differences both within the 14-d cycle and throughout the 17 injection cycles. The cows treated with VEL-rbST demonstrated a more variable 14-d milk yield response curve, with more pronounced valleys between injections compared with the ZSO-rbST formulation. In addition, only the ZSO-rbST treatment was effective in modifying the lactation persistency compared with control cows. Compared with the VEL-rbST formulation, the ZSO-rbST formulation yielded more kilograms of milk, fat, and protein with less milk variation throughout the seventeen 14-d lactation cycles for both primiparous and multiparous cows.
Highlights
Bovine growth hormone is a naturally occurring hormone in cattle that is responsible for growth regulation and milk production (Bauman, 1999)
Prior to the treatment period we found no significant differences among control, VEL-Recombinant bST (rbST), and ZSO-rbST cows for milk yield (P = 0.99), milk fat content (P = 0.37), milk fat yield (P = 0.32), milk protein content (P = 0.51), milk protein yield (P = 0.69), or the logSCC (P = 0.61)
Both VELrbST and ZSO-rbST had no effect on logSCC (P = 0.946), and both treatments reduced the average body condition score (BCS) compared with control cows (P < 0.001; Table 1)
Summary
Bovine growth hormone is a naturally occurring hormone in cattle that is responsible for growth regulation and milk production (Bauman, 1999). Recombinant bST (rbST) is a synthetically derived formulation of this hormone that has been developed to increase milk production efficiency in dairy cows and profitability in dairy herds. Recombinant bST increases lactation milk yield by altering the lactation curve. Does milk yield increase immediately upon rbST administration, but milk yield is maintained at a higher persistency throughout the lactation cycle compared with cows not supplemented with rbST (van Amburgh et al, 1997). A large body of scientific evidence demonstrates that rbST treatment of dairy cattle results in increased milk production (Downer et al, 1993; Huber et al, 1997). A 2014 meta-analysis review of the effects of rbST reported that it increases milk production by 4 kg/ cow per day over the course of a lactation (St-Pierre et al, 2014). More importantly for dairy producers, rbST increases profitability. A recently published study estimates an average cost savings from the use of rbST among New York dairy farms of 5.5%/kg of milk produced, or $2.67/100 kg of milk produced in 2013 (Tauer, 2016)
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