Relationships between the diet selected by grazing sheep and the herbage on offer

Abstract

Oesophageal extrusa samples were collected from sheep grazing monospecific swards of four temperate perennial grasses. The in vitro digestibility and the proportion of green plant material in the extrusa samples were related exponentially to the yield of herbage on offer. The digestibility of ingesta was highly correlated with the yield of green herbage. When the yield of green herbage exceeded c. 550 kg/ha the sheep selected a diet more digestible than the mean of the green plant material on offer, and when there were low amounts of green herbage available the ingesta was less digestible than the green plant material on offer because of the low proportion of green plant material eaten. A relationship between the proportion of green plant material in extrusa samples and the green herbage yield was determined for each species, and no significant difference in regressions between species was found. It is suggested that the pooled relationship obtained in this study may be used to predict the proportion of green plant material in the ingesta of sheep over a range of grass species and yields.