Changes in postprandial plasma and extracellular and ruminal fluid volumes in wethers fed or unfed for 72 hours

Postprandial shifts in body water compartments might limit feed intake by ruminants, especially when an animal becomes partially dehydrated during transportation or other periods of water deprivation. This experiment was conducted to determine the effects of feed and water deprivation on postprandial changes in body water compartments in wethers. Hampshire wethers (n = 8; average BW 42 +/- 2 kg) were used in a crossover design. During each period, four wethers were limit-fed (540 g DM/d: FED) and four were deprived of feed and water for 72 h (DEPRIVED). Wethers were infused i.v. with Evans blue and sodium thiosulfate and intraruminally with Cr- or Co-EDTA, after which blood and ruminal samples were collected for the next 4 h. All wethers were then fed 540 g of feed DM, and infusions were repeated 30 min after feeding. Body water compartment volumes were determined with linear regression using plasma concentrations of Evans blue (plasma volume), and sodium thiosulfate (extracellular volume), and using ruminal fluid concentrations of Cr or Co. Feed and water deprivation decreased (P < .01) extracellular water space but did not affect plasma or ruminal water space. After feeding, extracellular water space decreased (P < .01) and ruminal volume increased (P < .05) in the FED and DEPRIVED wethers. Plasma pools of Na, K, and Mg were not affected by feeding in FED wethers but decreased (P < .05) in DEPRIVED wethers. The increase in ruminal fluid pools of Na, K, and Mg were greater (P < .05) in FED than in DEPRIVED wethers. These results indicate that abnormal water and electrolyte shifts may be factors partially responsible for the decreased feed intake by ruminants subjected to transportation or feed and water deprivation stress.