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Impact of Dehydration on Production and Thermoregulation of Angus Steers at Thermoneutrality

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Livestock Environment VIII, 31 August – 4 September 2008, Iguassu Falls, Brazil  701P0408.(doi:10.13031/2013.25538)
Authors:   B Scharf, L E Wax, T J Evans, D E Spiers
Keywords:   Cattle, Water deprivation, Rehydration

It is known that ruminants undergo various physiological adaptations to cope with dehydration. Since the physiological mechanisms which enable ruminants to deal with water scarcity are only partly understood, a study was conducted to determine if dehydration would result in concentration of blood and urine to compromise thermoregulation. Eight Angus steers were acclimated for seven days at thermoneutrality (21C) in the Brody Environmental Center at the University of Missouri. This was followed by three days each of water restriction and rehydration. Rectal temperature and respiration rate were measured six times daily. Blood samples were taken prior to dehydration, and once daily during dehydration and rehydration. Body weight, food and water intakes, and cutaneous water loss at shaved sites were recorded during acclimation and daily during dehydration and rehydration. Steers lost 4 percent body weight during dehydration, but body weight returned to baseline within 24 hours of rehydration. Feed intake decreased (70 percent) within 24 hours of dehydration, and recovered after 24 hours of rehydration. Respiration rate and cutaneous water loss decreased with dehydration, which, combined with the reduction in feed intake, resulted in no physiological change in rectal temperature. Hematocrit was a variable indicator of dehydration, decreasing during the first 24 hours, before returning to baseline. Serum osmolarity increased within 24 hours without water and remained elevated until rehydration. Dehydration appeared more complex than rehydration, resulting in increases in some blood parameters and no change in others. In contrast, rehydration decreased in all blood parameters to suggest blood dilution.

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