Can nitrogen-fertilised ryegrass substitute for white clover?

Abstract

Sheep and cattle have difficulty satisfying their preference for white clover when it's proportion in pastures is low. We tested the hypothesis that they prefer clover because it has a higher concentration of nitrogen (N), and expected that they would reduce their preference for clover (increase their preference for grass) when grass had a higher concentration of N. In two experiments, mature sheep and growing cattle were offered choices between grass, having either a high or a low concentration of N, and white clover, growing as adjacent pure swards. To test the specific role of N in preference they were also offered each grass alone (sheep only) and a choice between the high and low N grass. Sheep and cattle preferred clover (75% of time grazing on clover and 25% on grass), but this preference was not affected by the concentration of N in the grass. They preferred the grass with a high concentration of N to that with a low concentration. Sheep and cattle detect differences in the N concentration of food items, but alter their grazing behaviour (express a preference) only when it does not affect dry matter intake or the proportion of clover in their diet. We conclude that N is not the reason why animals prefer white clover. Manipulating the N concentration in grass will not cause the switch in preference required for animals to easily satisfy their preference from typical mixed species pastures that are grass-dominant and have a low proportion of clover. Keywords: cattle, diet selection, food preference, grazing behaviour, nitrogen, sheep