Water, electrolyte and acid-base balance in transported Bos indicus steers
Parker, Anthony Joseph (2004) Water, electrolyte and acid-base balance in transported Bos indicus steers. PhD thesis, James Cook University.
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The objective of these studies was to investigate the physiological mechanisms involved in maintaining water, electrolyte and acid-base balance in Bos indicus steers placed under stress. These studies also sought to provide a novel approach to minimize the effects of stress on the physiology of Bos indicus steers during long haul transportation in the seasonally dry tropics.
Merino sheep provided a simulated stress response model, to evaluate the effects of the principle stress hormone cortisol on indices of water and electrolyte balance. This study indicated that stressed sheep suffer from a loss of body water in excess of that associated with a loss of electrolytes to support the hypothesis that elevated physiological levels of cortisol induce a diuresis in ruminants that contributes to dehydration.A second pen study was performed to investigate the effects of excess cortisol on physiological mechanisms that resist dehydration in Bos indicus steers. The presence of excess cortisol suppressed the RAA axis but did not markedly affect plasma AVP concentrations. This reflected the complexity of endocrine interactions associated with water balance in Bos indicus steers that enabled homeostasis to be maintained. A quantitative analysis of acid base balance in Bos indicus steers demonstrated long haul transportation or extended periods of feed and water deprivation to have no effect on blood pH. The primary challenge to a transported or feed and water deprived animal is a mild metabolic acidosis induced by elevated plasma proteins which may be the result of a loss of body water. The loss of electrolytes has little effect on the acid-base balance of the animals.
The treatment of Bos indicus steers prior to long haul transportation with the osmolyte glycerol provided a novel approach to conserving body water, decreasing the energy deficit and preserving muscle quality.
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