The use of polyethylene glycol as a marker for measuring rumen water volume and the rate of flow of water from the rumen of grazing sheep

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Abstract
The use of polyethylene glycol as a marker for measuring rumen water volume and the flow of water out of the reticulo-omasal orifice has been examined in grazing sheep. With grazing sheep the semi-logarithmic plot of marker concentration against time was curvilinear and so quadratic instead of linear regressions were fitted to the data. This procedure increased the statistical precision of estimating initial marker concentration. The error involved in estimating rumen water volume and flow rate in grazing sheep was greater than that of Hyden (1961a), whose animals were fed chaffed hay and kept under constant environmental conditions. Examples of rumen water volumes, total rumen DM contents, and flows of water out of the reticulo-omasal orifice have been presented for sheep grazing three different pasture types.