The Fate and Behaviour of Imbibed Water in the Rumen of Cattle

The quantity of imbibed water that bypassed the rumen directly or rapidly effluxed from the rumen was investigated in four steers offered water marked with CrEDTA. Water was offered for short periods designed to simulate the drinking patterns that occur under extensive grazing conditions. Animals were fed either low quality pangola hay in the long form or a concentrate diet. Bypass of imbibed water was calculated by difference from marker imbibed and that present in the rumen on emptying after water had been imbibed. It thus represents the passage of marked water directly to the omasum/abomasum and that which rapidly effluxed from the rumen before emptying. Bypass of imbibed marked water was 19.0 and 25.3 % for animals consuming pangola and concentrate respectively (significantly different from zero but no significant diet effect). Imbibed water entering the rumen mixed rapidly so that liquid from a posterior site in the rumen had a similar concentration of Cr to that from an anterior site in the proximity of the reticulum and cranial sac by about 1 h after drinking. There was no effect of rumen sampling site on the fractional outflow rate of CrEDTA (from imbibed marked water) from the rumen. It was concluded that most water which is drunk after a period of water deprivation will enter the rumen, mix rapidly and have a fractional outflow rate similar to other fluid in the rumen. The values derived may be used to calculate the amounts of supplement needed in drinking water if the target site is the rumen or intestines of cattle with intermittent access to water under extensive grazing conditions