Dietary preference of dairy cows grazing ryegrass and white clover.

The dietary preference of lactating dairy cows grazing perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) was studied. Twelve groups of 2 lactating, Holstein-Friesian dairy cows grazed 1.2-ha plots containing conterminal monocultures of clover and grass. Half of the groups grazed a plot containing 75% clover and 25% grass (by ground area), with the remaining groups grazing a plot containing 25% clover and 75% grass. The intake rates of clover were higher than those of grass, and intake rates were higher in the evening than in the morning. During daylight hours, clover formed 63.2% of the diet of the groups offered 25% clover, which was higher than the 25% offered but lower than preference for 100% clover. This indicated that cows showed a partial preference for clover, with an overall value (i.e., the mean of the 75% and 25% clover groups) of 73.8%. There was a diurnal pattern to preference, with a stronger preference for clover in the morning and with the preference for grass increasing during the day. The basis for partial preference remains unclear and warrants further research.