Studies on the nutritive value of the diet selected by grazing sheep. I. Differences in composition between herbage consumed and material collected from oesophageal fistulae

Abstract

Freshly-cut forages and lucerne chaff were given to penned sheep fistulated at the oesophagus. The feed given and the samples obtained through the fistula were analysed for in vitro digestibility, nitrogen, ash, phosphorus, sodium, potassium and calcium. Organic matter digestibility was predicted from the in vitro determination. Three regression equations were calculated relating predicted organic matter digestibility of the feed to the digestibility of the extrusa sample. The most precise of these equations had a residual standard deviation of ±3·4 units. The relationship between the nitrogen contents of the feed and sample was calculated. The equation did not pass through the origin but the differences in nitrogen content between feed and extrusa were small over the range 4·69 to 1·28% N included in this study. The nitrogen and calcium contents of the feed could be estimated from the sample with errors of ±7·5 and 9% respectively. The sodium, potassium and ash contents of the diet could not be reliably estimated from an oesophageal sample.