Respiratory hypocapnia at different stages of lactation during long-term exogenous bovine somatotropin in crossbred holstein cattle in the tropic

Abstract

The aim of this study was to investigate the influence of long-term administration of recombinant bovine somatotropin (rbST) on the acid-base homeostasis of lactating crossbred cows under hot and humid condition of Thailand. Two groups of five animals each of primiparous crossbred dairy cattle were supplemented either with rbST or with control vehicle every 14 days throughout the period of lactation. The blood gas parameters, milk yield and feed intake from both groups were recorded at each stage of lactation. Cows supplemented with rbST showed mild degree of acid-base imbalance during early to mid lactation. The lower partial pressure of carbon dioxide (p aCO 2) and plasma bicarbonate ([HCO 3-]a) from arterial blood were apparent at early stage of lactation as compared with those of the control cows. The present results can conclude that rbST supplementation influences acid-base homeostasis. The supplementation of rbST may cause the respiratory hypocapnia under prolonged moderate heat exposure and high milk production.