Summary 1.Equids are generalist herbivores that co-exist with bovids of similar body size in many ecosystems. There are two major hypotheses to explain their co-existence, but few comparative data are available to test them. The first postulates that the very different functioning of their digestive tracts leads to fundamentally different patterns of use of grasses of different fibre contents. The second postulates resource partitioning through the use of different plant species. As domestic horses and cattle are used widely in Europe for the management of conservation areas, particularly in wetlands, a good knowledge of their foraging behaviour and comparative nutrition is necessary. 2. In this paper we describe resource-use by horses and cattle in complementary studies in two French wetlands. Horses used marshes intensively during the warmer seasons; both species used grasslands intensively throughout the year; cattle used forbs and shrubs much more than horses. Niche breadth was similar and overlap was high (Kulczinski's index 0·58-0·77). Horses spent much more time feeding on short grass than cattle. These results from the two sites indicate strong potential for competition. 3. Comparative daily food intake, measured in the field during this study for the first time, was 63% higher in horses (144 g DM kg W -0·75 day -1 ) than in cattle (88 g DM kg W -0·75 day -1 ). Digestibility of the cattle diets was a little higher, but daily intake of digestible dry matter (i.e. nutrient extraction) in all seasons was considerably higher in horses (78 g DM kg W -0·75 day -1 ) than in cattle (51 g DM kg W -0·75 day -1 ). When food is limiting, horses should outcompete cattle in habitats dominated by grasses because their functional response is steeper; under these circumstances cattle will require an ecological refuge for survival during winter, woodland or shrubland with abundant dicotyledons. 4. Horses are a good tool for plant management because they remove more vegetation per unit body weight than cattle, and use the most productive plant communities and plant species (especially graminoids) to a greater extent. They feed closer to the ground, and maintain a mosaic of patches of short and tall grass that contributes to structural diversity at this scale. Cattle use broadleaved plants to a greater extent than horses, and can reduce the rate of encroachment by certain woody species.

With 2 figures in the text)We describe food selection by roe deer (Cuprealus capreolus) in relation to the food quality of the plants available (the concentrations of fibres, sugars, crude protein, and of phenolics and terpenes). Seven tame roe deer feeding in an oak-beech woodland edge used the majority (SO-94%) of the plant species available: they were therefore generalist feeders. However, they preferred only a small number of plant species in the different seasons: ivy (Hederu helix) in winter and autumn, dogwood (Cornus spp.) in summer, hornbeam (Curpinus befulus), hawthorn (Crutuegus spp.) and bluebells (Hyacinthoides non-scriptu) in spring. No preference or avoidance could be demonstrated for 74-85% of the available species, but 7-12 species were avoided according to the season. Though the avoided species were sometimes common, they never comprised an important part of the diet. In contrast, the preferred species made up only 4-13% of the available green matter but composed a large part of the diet (22-49%). Although generalists, the roe deer were therefore also highly selective feeders. The use of the different plant species was influenced by their availability, but to a different extent in the different seasons. Use of the plant species correlated negatively with the fibre content, as predicted from the digestive morphology of this concentrate selector. Preference/avoidance was related to the concentrations of soluble sugars, but not the crude protein content. Contrary to expectation, the roe deer preferred plants with a high concentration of protein-binding phenolics, suggesting that this deer has specific mechanisms for de-activating these compounds. Among the nutritional consequences of the feeding strategy of roe were a 17-35% higher soluble sugar content of the diet compared with the available green plant tissues, and an even greater increase in the phenolics. The crude protein contents and the dry matter digestibility of the diets tended to be slightly higher, and the fibre contents were lower, than those of the available green plant tissues.

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Summary — The composition and digestibility by sheep of 15 commercial maize varieties and 1 brown mid-rib experimental hybrid was measured over 2 yr in 7 locations, according to earliness as fresh-cut forage from the milky stage of the grain to the glazed stage. This study determined the effect of the main factors causing variations in plant composition and digestibility. Under satisfactory growing conditions, the digestibility of a given maize hybrid increases significantly with growth stage, whereas it changes very little under poor conditions (low temperatures, drought, etc). For a given dry matter content, genotype effects were significant in only 2 locations and were of similar importance to those of environment (location and year) on a given genotype. As for other forage crops, maize digestibility is closely linked (R = 0.98) to its undigestible cell wall content. In contrast, the digestibility of maize cell walls is not only independent of their content in the plant but also lower than that of other forage crops (-10

Summary — Stalks of several normal maize hybrids, displaying a broad range in cell-wall digestibility, were examined for lignin content