Submitted to: Grassland International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/5/2001
Publication Date: N/A
Interpretive Summary: Intake of the grazing animal is the most important determinant of animal performance. The identification of sward characteristics that favor high intake would be useful in understanding how pastures might be managed to maximize intake of the grazing animal. The herbage on-offer has characteristics as leaf bulk density, tiller numbers and weight and a degree of vertical variation in bulk density as well as in nutritive value As animals ingest forage the rate and amount consumed can vary causing differences in bite volume, bite weight and bite rate. Also associated with how the pasture canopy is presented to the animal is the time the animal will spend grazing. The animal selects green leaf in possible. In cases where a lot of dead tissue is present or if the stem and leaf are not easily separated the animal will either spend a lot of time trying to select the green leaf, or will decide to eat leaf and stem. This can reduce intake as animals only spend a certain amount of time grazing or it may limit the nutritive value of the diet selected. Either of these will reduce animal performance. The degree to which these differences among pasture species are understood have important application to the grazing management strategy that needs to be implemented to maximize animal daily performance.
Technical Abstract: Compared to temperate systems, there have been few detailed assessments of canopy characteristics and associated grazing behavior in planted tropical grasslands. Reasons include the large number of forage species used in warm climates, the diversity of their morphology, research priorities emphasizing germplasm evaluation and management, and limited resources. This review describes canopy attributes of C4 grass pastures, highlights the most important relationships between grazing behavior and these canopy characteristics, and discusses the implications of canopy characteristics and grazing behavior for long-term intake and animal performance. It is suggested that the largest differences in canopy characteristics between tropical and temperate swards are not total canopy measures but those of the upper canopy strata including leaf proportion and bulk density. This occurs because tropical swards, unlike many temperate ones, have large vertical heterogeneity in density, plant-part proportion and nutritive value. In temperate swards, bite weight is primarily a function of sward height, but leaf percentage, leaf mass, or green herbage mass of the upper strata of the canopy usually are more important with C4 grasses. The manner in which leaf is presented to the animal and the degree to which it can be prehended separate from stem and dead material of low digestibility are also of great significance in pastures based on C4 grasses.