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I. Comparisons were made between castrated male Scottish Blackface sheep and red deer (Cervus eluphus) of voluntary forage intake (VFI), digestibility and the mean retention time (MRT) of a particulatephase markel ('OSRu-phenanthro1ine) in the alimentary tract, when a range of forages: dried-grass pellets, chopped dried grass, fIesh-frozen Agrosris-Festucu spp. and heather (Cullunu vulgaris, L. Hull) were given at different times of the year.2. On both the dried-grass-pellet and chopped dried-grass diets the red deer and sheep ate similar quantities. Both species had a higher VFI of dried-grass pellets in July than in November. The sheep digested the dried-grass-pellet diet better than the red deer and this was associated with a longer MRT of the particulate-phase marker in the alimentary tract.3. The VFI of Agrosfis-Festuca spp. and heather by the red deer was twice that of the sheep. The VFI of heather by the sheep increased by 32 % between January and April, and the VFI of both the AgrostisFestuco spp. and heather diets by the red deer increased by 65-70 %. The sheep digested the Agrostis-Fesfucu spp. better than the red deer but the red deer digested the heather slightly better than the sheep. MRT of the particulate-phase marker was greater for the sheep than for the red deer on both diets.The digestibility and MRT of both diets in the red deer did not decrease with the seasonal increase in VFI, suggesting a possible hypertrophy of the alimentary tract.Domesticated sheep and feral red deer (Cervus elaphus) are the principal producers of food for human consumption from a large proportion of the rough grazings of Scotland.In any study of land use or resource management it is necessary to know whether there are differences between the two species in the biological efficiency with which they use the resource. These can be brought about by differences between the species in their grazing behaviour, ability to consume more of a diet and digest it better, in their efficiency of utilization of the end-products of digestion and in their nutrient requirements. It is the second aspect which is examined in this paper. Sheep and red deer eat many similar plant species which range from highly digestible grasses in summer to poorly digested grasses and heather (Calluna vulgaris, L. Hull) in winter (Hobson, 1969), but seasonal fluctuations in voluntary intake by red deer (Simpson, 1976) and other Cervidae (Long, Cowan, Strawn, Wetzel & Miller, 1966;McEwan & Whitehead, 1970) would appear to be greater than those found with sheep (Gordon, 1964). Preliminary results of Kay & Goodall (1976) have indicated that with good-quality roughage diets there were only small differences between sheep and red deer in voluntary intake (VFI), digestibility and mean retention time of undigested residues in the gut. However, comparisons using poor quality roughages have not been made.The present experiments were designed to examine the differences between the sheep and the red deer in VFI, digestibility and mean retention time of a particulate...

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A series of twenty-four swards containing different proportions of white clover (OOO-O55) and perennial ryegrass were created by using different seed mixtures, herbicide applications and previous cutting frequencies. These swards were used to study the diet of oesophagcally-fistulated wether sheep which grazed the various swards for a 30-min period after 1. 2 and 3 weeks of regrowth.The proporiion of white clover In the diet was generally greater than that in the sward. Fiftyseven percent ofthe variation in the proportion of white clover in the diet could be attributed to the proportion ofwhite clover in the sward. White clover and perennial ryegrass leaf and stem were grazed to the same height and the proportion of white clover in the grazed horizon of the sward explained 83% ofthe variation in the proportion of white clover in the diet. The proportion of white clover in the diet was greater than the proportion in the grazed horizon of the sward in week 3 of regrowth, but not in weeks 1 and 2. and greater when the proportion of white clover in the grazed horizon was lower than 0-40. Both these observations were interpreted as indicating selec-tion for white clover by the sheep within the grazed horizon.There was a positive and linear relationship between ,the depth of the grazed horizon and sward height which, together with the relationship between the proportion of white clover in the grazed horizon and in the diet, would allow the prediction ofthe proportion of white clover of the diet from the height and the white clover content of the grazed horizon of the sward.