Abstract
The effect of recombinant somatotropin (rbST) application in cattle has been demonstrated in temperate climate but very limited studies are available in tropical regions. The objective of this study was to compare the effect of the application of two different formulations of rbST on the milk yield and body condition of dairy cattle in a commercial herd under intensive production in Peru. We evaluated the application of 500 mg of active rbST in a zinc sesame oil (ZSO-rbST; n = 44) or vitamin E lecithin (VEL-rbST; n = 45) vehicle while control cows (n = 42) did not receive any application. The application of rbST was performed by every 14 days for 12 cycles, for a total of 168 days. The application of rbST increased the milk production of primiparous and multiparous cows by 3 and 3.2 kg/day for the VEL-rbST formulation respectively when compared with control cows (p < 0.01) and no difference in milk production was observed between the ZSO-rbST formulation and the control group (p > 0.05). However, no significant difference on milk production was observed between the rbST formulations evaluated. The effect of rbST per injection cycle indicated differences in milk production and economic return for the 12 cycles between rbST and control in primiparous group, while in multiparous, no differences were found between ZSO-rbST and control (p > 0.05), but differences were observed between VEL-rbST and control in 41% of the cycles (p < 0.05). No differences in body condition were found between the two rbST formulations and the control group during the evaluation. In conclusion, the application of rbST promoted higher milk production of cattle which had a positive impact on the economic income of the farmer.
Highlights
Bovine somatotropin, known as bovine growth hormone, is a natural protein secreted by the anterior pituitary gland (Estrada and Shirley, 1989) and the circulating concentration is positively correlated with milk production and mammary gland development (Fesseha et al 2019)
No differences in milk production were found between the ZSO-recombinant somatotropin (rbST) and control groups or between the two rbST formulations evaluated
When the effect of rbST per injection cycle of 14 days was analyzed, in primiparous cows, differences in milk production were found in the 12 cycles between the two rbST formulations in comparison with control cows, while in multiparous cows, differences were found between VELrbST and the control in 41% of the cycles but not between ZSO-rbST and the control for both primiparous and multiparous cows
Summary
Bovine somatotropin (bST), known as bovine growth hormone, is a natural protein secreted by the anterior pituitary gland (Estrada and Shirley, 1989) and the circulating concentration is positively correlated with milk production and mammary gland development (Fesseha et al 2019). BST regulates the partitioning of nutrients and its application increases milk production due to improvements in the availability and use of nutrients for. Using a meta-analysis of 26 studies of the effect of rbST, the administration of rbST to dairy cows increased milk production by 4.0 kg/day without adverse effects on the health of the cows (St-Pierre et al 2014). Mellado et al 2011; De Morais et al 2017) This can be attributed to the fact that primiparous cows are still growing and they have higher levels of endogenous bST than multiparous (McBride et al 1988), the nutrients are still being distributed to cover growth requirements in addition to the requirements for milk synthesis (Wathes et al 2007). Loss of body condition or body weight of lactating cows could have negative effect on their milk production (Roche et al 2007)
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