Interactions of Circulating Metabolic Hormones and Metabolites of Crossbred Holstein Cattle in Response to Supplemental Recombinant Bovine Somatotropin (rbST) and Cooling Management with Misters and Fans at Different Stages of Lactation in the Tropics

摘要

The low milk production of both exotic and crossbred cattle is still the main problem in dairy farming in the tropics. A shorter persistency of lactation of crossbred cattle has been shown to relate to a rapid decrease in the plasma bovine somatotropin as lactation progressed to mid and late lactation. However, the mechanisms relating to high environmental temperature and the role of endocrine system in regulating milk production remain to be investigated. The purpose of this study focused on interactions of metabolic hormones, feed intake and other variables relevant to milk synthesis during exogenous rbST in crossbred 87.5% Holstein Friesian (HF) cattle housed under cooling management with Misters and Fans (MFC). Ten primiparous cattle were divided into two groups of five cows each housing in Normal Shaded (NS) as a non-cooled group and in shaded with MFC as a cooled group. Each cow was administered of recombinant bovine somatotropin (rbST) with three consecutive treatment with 500 mg of rbST in every 14 days in early, mid and late stages of lactation. Ambient temperatures and THI at MFC barn were significantly lower. Both MFC and rbST treatment had significantly effect on rectal temperature and respiratory rate. The cooled cows significantly increased in DMI and milk yields and more responses to the effect of rbST administration. The positive energy balances were seen throughout experimental periods. Both plasma concentrations of Free Fatty Acids (FFA) and milk fat were significantly elevated by rbST administrations in both groups. Plasma thyroxin (T4), cortisol and insulin levels remained unchanged. Cooled cows showed significant low in the concentration of plasma leptin while plasma IGF-1 were significantly elevated and plasma leptin were significantly decreased during administrations of rbST. These findings demonstrate that both IGF-1 and leptin responses were the prominent mediators of rbST in stimulating the galactopoiesis in both groups but were regulated differently. A significant response to rbST with the high concentrations of plasma IGF-1 would share a role in stimulating milk production direct to the mammary gland function. The appearances of low plasma leptin levels due to the effect of cooling management and the lipolytic effect of rbST administration in either group, resulting subsequently increased DMI in the supply of nutrients to the mammary gland for facilitating milk synthesis.