Relationships between metabolic endocrine systems and voluntary feed intake in Merino sheep fed a high salt diet
Dominique Blache A D , Micaela J. Grandison A , David G. Masters B C , Robyn A. Dynes B C , Margaret A. Blackberry A C and Graeme B. Martin A CA School of Animal Biology M085, Faculty of Natural & Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
B CSIRO Livestock Industries, Centre for Environment and Life Sciences, Private Bag 5, Wembley, WA 6913, Australia.
C Cooperative Research Centre for Plant-based Management of Dryland Salinity M081, Faculty of Natural & Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
D Corresponding author. Email: dbla@animals.uwa.edu.au
Australian Journal of Experimental Agriculture 47(5) 544-550 https://doi.org/10.1071/EA06112
Submitted: 1 April 2006 Accepted: 19 October 2006 Published: 13 April 2007
Abstract
Grazing saltbush reduces productivity in sheep mostly because the high salt intake decreases feed intake and challenges the metabolism of the animal. However, little is known of the effect of salt load on the endocrine control systems that regulate voluntary feed intake and metabolism. Plasma concentrations of leptin, insulin and cortisol and blood glucose were monitored in wethers fed for 2 weeks with either a control diet (adequate salt) fed ad libitum, a high salt diet (20% of dry matter) fed ad libitum or a group fed the control diet with an intake restricted to that of the high salt ad libitum group (control pair-fed). High salt intakes reduced voluntary feed intake within 1 day and circulating concentrations of insulin and glucose within 2 weeks. Liveweight and leptin concentrations were not specifically affected by the high intake of salt but decreased in response to the decrease in intake. Cortisol secretion was not affected. Although salt intake had a specific effect on insulin and glucose (over and above the effect of reduced feed intake alone), the reduction in insulin would be expected to increase rather than decrease appetite and feed intake. Therefore, insulin, leptin and cortisol do not appear to play major roles in the control of feed intake in sheep consuming high levels of salt.
Additional keyword: salinity.
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