Forage Intake and Grazing Performance by Dairy Cows

A S early as the late eighteenth century stockmen were concerned with the relationship between pasture forages and the behavior of animals grazing them. James Anderson (1797), who farmed in Scotland, described grazing habits of animals and outlined certain procedures which he felt would give greater production from pastures. One hundred and forty years elapsed before any further large-scale studies were reported in which an effort was made to relate the effects of forage characteristics to the grazing and milk production of dairy cows. Hancock (1950)) working under New Zealand conditions, reported the conclusions drawn from four years’ work during which nearly 2,000 cow-days of grazing were recorded. While the data from which the observations were made were not reported, several of the conclusions are of great interest to workers in the field of grassland management. Of particular interest is the observation that the time spent grazing and the subsequent time required for ruminating are interdependent. Either of the periods may be limited or prolonged by the other and, in the case of prolonged ruminating time, total forage intake may be limited by insufficient time for grazing. To enable this relationship to be depicted, the use of the formula ( ruminating time grazing time = rt/gt ratio > was suggested and used in this paper. The relationship between grazing behavior and the quantity and quality of forage available per cow is perhaps the newer and more interesting of the reported findings. Waite, et al. (1951) reported on two years’ work in Scotland during which an effort was made to relate the forage conditions, grazing behavior, and other factors to the forage intake of the animals under study. He explained the difference in intake between forages characterized as long stemmy material of low moisture content and its opposite on the basis that the rumen is less densely packed when the animal receives the feeling of repletion, thus, giving shorter grazing periods and less dry matter intake. On the short materials of high moisture content, the forage tends to pack in the rumen and the animal grazes longer and takes a greater quantity of forage into the rumen before the state of fullness is reached. The workers found no apparent relationship between the time spent grazing and stage of lactation, individual milk yield, or live weight. It is the purpose of this paper to describe the techniques being used at the Georgia Experiment Station and some of the preliminary data obtained during the first phases of a long-time study of pasture utilization by dairy cows.