PLANT-RESPONSE TO GRAZING - A REVIEW

Knowledge of the potential responses of forage plants to grazing by different classes of livestock has application in grassland research and management. Cattle (Bos taurus) are less adapted to graze individual plant parts (leaves vs. stems) selectively than are sheep (Ovis aries), goats (Capra hircus), or horses (Equis caballus). Diet preference differs among animal types and this may influence botanical composition and productivity of the sward. An example reported from grazing white clover (Trifolium repens L.)-ryegrass (Lolium spp.) pastures showed that lambs consumed greater portions of white clover and smaller portions of grass and dead material than calves. The diet selected by goat kids was intermediate between that selected by calves and lambs. Different grazing intensities may change the morphology of plant growth. Animals may affect pasture composition and growth from treading and through their deposits of dung and urine. Generally, legumes are less resistant to treading than grasses. On P-deficient soils, cattle dung tends to promote legume growth and N in the urine promotes grass growth. Thiamine from herbivore saliva deposited during grazing may promote subsequent regrowth of grasses. Incorporation of animal defoliation in the early phases of forage evaluation is recommended for characterizing plant responses to grazing livestock.