A grazing trial was condueted at the Miller Pordue Memorial Farm, Upland, Indiana, USA. during the growing seasons of 1960 and 1%1. The pastures used were 1 year old leys planted to a mixture of alfalfa and bromegrass and were stocked with a uniform group of yearling Hereford under the "put and take" system. The experimental design was a randomized complete block with 3 treatments and 4 replications.
The first treatment, where the pastures where stocked to their carrying capacities was used to determine the other two. In one of them, 30% less animals were used, the pastures being undergrazed and in the other 40% in 1960 and 30% in 1961 more animals were used, the pastures being overgrazed.
Since only subjective estimates were used to determinethe forage availability, the grazing preassure each of the treatments were receiving was not known. This implies that the treatment were not fixed throuhout the season but they varied according to the visual estimates of their carrying capacities, therefore statistical treatment of the data was not possible.
The average daily gain, as an indicator of forage quality shows that there is a decrease in forage quality as the experiment progressed into the season. This may be due to herbage maturation or other physiological aspects.
The output per hectarea, considered as an indicator of quantity of forage produced, shows that as the season progressed there was a decrease in the availability of herbage, wich can be associated with seasonality of pasture production.
The optimum stocking rate produces the higher output per hectare. The average daily gain decreases if the stocking rate is increased but at low leveIs this is compensated by the higher animal numbers. However, if grazing selectivity is strongly limited and the animal herbage consumption is restricted by increasing the animals in the pasture, the output per hectare is decreased when a stocking rate of approximately double the one at carrying capac

1 Ing. Agr., Ph. D. Coordinador de Investigaciones Ganaderas, Instituto de Investigaciones Agropecuarias, Casilla 5427, Santiago, Chile.
2 Professor of Agronomy, Department of Agronomy, Purdue University, Lafayette, Indiana. Dirección acutal: Department of Agronomy, University of Florida. Gainesville, Florida, U.S.A.