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High intakes of NaCl by sheep especially in the arid and semi-arid grazing areas of Australia contribute to deaths and reduced production. The performance of sheep exposed to high intakes of NaCl is well documented but the basis of the tolerances shown are not well understood especially in young sheep. Homeostasis is maintained by integration of body systems that is determined by an animal's genotype. Studies presented were undertaken to evaluate the productive performance of young sheep exposed to high intakes of NaCl from an early age. Information to aid in the understanding of the complex homeostatic mechanisms was obtained. Young sheep were given a fixed daily oral dose of NaCl to standardize the challenge and a number of variables measured over a period of several months. ... Detrimental effects on growth and wool production were observed when young sheep received chronic high intake of NaCl from an early age. Body water, Na+ and Cl- pools and fluxes were changed and this affected food intake-water intake relationships. Renal responses were efficient when lambs were subjected to NaCl challenges. No permanent modifications of function appeared to occur. Changes of rates of function of the renal and gastrointestinal system and body water, Na+ and Cl- pools and fluxes appear to be the mechanisms that sheep utilise to tolerate NaCl loads. An integration of body systems and functions occur to enable sheep to tolerate a high intake of NaCl. Other factors such as behavioural responses, circadian rhythms, climate and weather conditions also affect the tolerance to NaCl. Genotype-phenotype interactions determine the levels of tolerance that enable maintenance of homeostasis. Research in areas where knowledge is lacking would provide a better understanding of osmoregulation during stresses such as a NaCl load. |
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