Abstract
Eighteen young growing pigs of the Large White breed were housed in individual pens or metabolism stands and habituated to drinking their water from a bowl. Those housed in the metabolism stands were surgically fitted with a catheter placed in he jugular vein to allow collection of blood samples. The voluntary intake of water after periods of progressively increasing water deprivation was measured. The measurements were made by allowing the pigs to drink to satiety after either a 2, 4, 8, 12 or 18 h period of water deprivation. Voluntary water intake was a function of the duration of water withdrawal and the rate of intake increased with progressive deprivation. Changes in plasma concentration of sodium and protein, haematocrit and osmolality could be detected after 12 and 18 h of dehydration. The progressive changes in plasma sodium concentration ([Na+]), osmolality, protein concentration and haematocrit during adaptation to dehydration when water was withheld for 72 h were examined in six pigs. Using a technique of continuous blood sampling, the rapid changes in the same blood parameters during rehydration, when water was made freely available at the end of the 72 h period, were also monitored. The [Na+] and osmolality dropped precipitously following the onset of drinking. From the 15 min stage to the 4 h stage with water available ad libitum, the values of both parameters remained below their control levels. However, the plasma protein concentration and the haematocrit values remained significantly above their pre-dehydration control levels up to the 4 h stage, even with water freely available, thus showing that drinking stopped even though the extracellular fluid phase remained dehydrated. Only with food available did the blood measures return to normal. It is concluded that the cellular fluid phase forms an integral part of the mechanisms involved in the termination of drinking in the pig.
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