To develop sustainable grazing systems based on mixtures of plant species and animal species, it is important to understand how much, and from which plant species animals eat. A prerequisite in the development of this understanding is a knowledge of dietary preference. Sheep have been shown to have a preference for about 70% clover in their diet (Parsons et al., 1994), but similar information is not available for cattle. It has been observed that grass/clover swards grazed by cattle often contain more clover than those grazed by sheep. This has been interpreted to imply that cattle have a lower preference for clover than do sheep. However, cattle are alleged to graze less selectively than sheep (Phillips, 1993) because of their mouth size and structure and so, the greater proportion of clover observed in swards grazed by cattle, may not reflect dietary preference but their relative inability to select. The preference for clover by cattle was tested by offering a choice of grazing from adjacent monocultures of grass and clover. It was anticipated that diets containing high proportions of clover might predispose cattle to bloat, and so half the animals received an anti-bloat prophylactic, to test whether this prevented bloat and modified preference.