Experimental design for grazing trials

Animal production in grazing experiments depends both on treatment and on stocking rate. Production at optimum stocking rate is the only valid measure of treatment effect and treatment comparisons should be based on this criterion. Since optimum stocking rates are unknown these comparisons cannot be made directly, instead they must be in-ferred from the results obtained with the stocking rates actually used. This requires that some form of production stocking rate relationship be postulated. This paper sug-gests a form for this relationship and considers its implications on experimental design and particularly on the number of stocking rates per treatment. The evaluation of treatment effects on animal production from grazed pasture is complicated by the interaction of treatments with stocking rate. It is now widely recognized that comparing treat-ments at a single common stocking rate does not give a true measure of treatment differences. A fair assessment of treatments requires that they be com