The Thai Journal of Veterinary Medicine


The aim of this study was to investigate the influence of long-term administration of recombinant bovinesomatotropin (rbST) on the acid-base homeostasis of lactating crossbred cows under hot and humid condition ofThailand. Two groups of five animals each of primiparous crossbred dairy cattle were supplemented either with rbSTor with control vehicle every 14 days throughout the period of lactation. The blood gas parameters, milk yield andfeed intake from both groups were recorded at each stage of lactation. Cows supplemented with rbST showed milddegree of acid-base imbalance during early to mid lactation. The lower partial pressure of carbon dioxide (paCO2) andplasma bicarbonate ([HCO3-]a) from arterial blood were apparent at early stage of lactation as compared with thoseof 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 andhigh milk production.

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