Selective grazing by sheep of two forage species at different stages of growth

Abstract

In a series of experiments where the rate of stocking was such that consumption exceeded growth, sheep continuously grazing pastures of lucerne or Phalaris tuberosa exhibited distinct preferences. On both forages sheep continuously selected leaf in preference to stem where this was physically possible. Within both leaf and stem fractions of the plants selection was for material of the highest available nitrogen content. This resulted in the sheep presenting themselves each day with material of a lower nitrogen content than that of the previous day. Evidence is presented to show that these selection preferences were exhibited more strongly the greater the amount of material present per unit area, i.e. the more mature the plant. The process of grazing in a horizontal plane, together with selection in a vertical one, is also described.