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.

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Food intake is a key biological process in animals, as it determines the energy and nutrients available for the physiological and behavioural processes. In herbivores, the abundance, structure and quality of plant resources are known to influence intake strongly. In ruminants, as the forage quality declines, digestibility and total intake decline. Equids are believed to be adapted to consume high-fibre low-quality forages. As hindgut fermenters, it has been suggested that their response to a reduction in food quality is to increase intake to maintain rates of energy and nutrient absorption. All reviews of horse nutrition show that digestibility declines with forage quality; for intake, however, most studies have found no significant relationship with forage quality, and it has even been suggested that horses may eat less with declining forage quality similarly to ruminants. A weakness of these reviews is to combine data from different studies in meta-analyses without allowing the differences between animals and diets to be controlled for. In this study, we analysed a set of 45 trials where intake and digestibility were measured in 21 saddle horses. The dataset was analysed both at the group (to allow comparisons with the literature) and at the individual levels (to control for individual variability). As expected, dry matter digestibility declined with forage quality in both analyses. Intake declined slightly with increasing fibre contents at the group level, and there were no effects of crude protein or dry matter digestibility on intake. Overall, the analysis for individual horses showed a different pattern: intake increased as digestibility and crude protein declined, and increased with increasing fibre. Our analysis at the group level confirms previous reviews and shows that forage quality explains little of the variance in food intake in horses. For the first time, using mixed models, we show that the variable 'individual' clarifies the picture, as the horses showed different responses to a decrease in forage quality: some compensated for the low nutritional value of the forages by increasing intake, few others responded by decreasing intake with declining forage quality, but not enough to cause any deficit in their energy and protein supplies. On the whole, all the animals managed to meet their maintenance requirements. The individual variability may be a by-product of artificial selection for performance in competition in saddle horses.

The horse industry has soared in Europe in the last decades. This article analyses the existing and possibleinteractions between horses and rangelands, by taking horse feeding as well as environmental and socio-economic issues into consideration. Due to the amount of recent data available for France, this country serves asa case study for the EU. Even though rangeland-based feeding is common in traditional horse-farming systemsand still exists today on some pastoral farms, most horses are fed on conserved forage and concentrates,especially when the economic value of the horse is high. Scientific literature and recent field data suggest that rangelands can be used as the main feed source for mares and growing horses, providing not only nutrition but also a suitable environment for training and welfare. Horses can contribute to the sustainable development of rangelands, if they are well integrated into the local agricultural context and if horse grazing is carefully managed. To achieve this, a better integration of horses in the agricultural sector (from the field to research activities) is needed. Anissue of utmost importance is the access of horse owners to land and technical support, taking into accountthat horses are herbivores similar to ruminants, as well as the peculiarities of the horse industry