PLANT-ANIMAL INTERFACE

The grazing system, consisting of soil, plants, and animals, is a dynamic system. The plant-animal interface describes the continuum of interactions of the grazed with the sward. The plant grows and produces its tissues, ultimately for reproduction and persistence. The grazer harvests parts of the plant which provide nutrients for maintenance and production. Conventional research approaches have included studying one of the components while either ignoring the others or attempting to hold them static. These conventional approaches also tend to measure responses over long periods, seldom less than a grazing season of 3 to 4 months, and the responses measured are net production, usually weight gain or net herbage accumulation. Gain is influenced by many factors, including characteristics and stage of growth of both the plant and the animal. Measurements of grazing behavior, which include grazing time, rate of biting, and bite size, lend themselves to short-term assessment of responses and compensations, which the animal often makes when foraging is restricted for some reason. For instance, when forage is limited in a predominantly grass system, the size of individual bites is reduced. The grazer may compensate by increasing rate of biting or time spent grazing or both, but the compensation is limited to about 15%. These measures are often responsive to differences in sward structure and availability. Short-term intake can be calculated from measures of grazing behavior and inferences can be made concerning the grazing strategy of various kinds of grazers. These measures may be an aid in the development of ecological and production models of the grazing system.