The use of the animal as a means of evaluating pasture is an obvious approach to the problem, since this is the form in which the practical man will ultimately measure the return from his grassland. If anything has to be sacrificed it is the sward and not the animal, a point too often overlooked in our grassland work generally. Though many grazing trials of an observational nature are to be found in the early agricultural literature, the earliest experimental work was most probably that of the late Sir William Somerville. When Professor of Agriculture at Newcastle in 1897, he commenced the world-famous experiment at Cockle Park Agricultural Experimental Station on pasture improvement. An effort was then made to measure the effect of various systems of manuring in terms of the live-weight increase of sheep grazing on the different plots. In this experiment on Tree Field the relative values of the different systems of manuring were measured by weighing the sheep before and after the experimental period. In the early years the plots were stocked with hoggs, but in order to get closer grazing lambs and ewes are now used and have shown greater increases per acre.