ABSTRACT
The forage-animal interface terminology was introduced by scientists to describe component relationships and interactions between plants and the grazing animal. The interface pertains to physiological, morphological, and chemical aspects of forage in response to defoliation, treading, and behavioral aspects of the grazing animal, and to modifications in grazing behavior in response to changes in the forage. Livestock managers and scientists investigating principals of cause-and-effect have sought understanding of the dynamics of the grazing and digestive processes[1,2] as a means of optimizing livestock production. Developments in forage-livestock systems research progressed from observation and inductive reasoning to statistical computational methodology to simulation modeling by the 1960s.[3] Grazing behavior and nutrient intake are interrelated to the extent that those components of grazing behavior that reduce intake or change diet selectivity also affect the rate and composition of nutrient intake.[4] We illustrate some interactive components of the plant-animal interface (Fig. 1), and include results of short-term research of grazing behavior, intake, and forage traits.[5,6]
DIURNAL PATTERNS AND TIME SPENT GRAZING
The diurnal pattern of grazing, rumination, rest, and drinking affects the daily routine of the ruminant. In both hemispheres, major grazing periods begin about dawn and late afternoon, and terminate near dark.[7] As day length
shortens, grazing periods lengthen until mid-winter, and in latitudes of 20° or more, grazing is nearly continuous during the daylight period. In tropical environments with high temperature and humidity, and with similar length of day during the year, cattle graze primarily at night. When daily maximum temperatures were <15°C, limited night-time grazing occurred, but when temperatures were >25°C, night-time grazing increased to as much as 70% of the total time spent grazing.[7] Time spent grazing during a 24-hr period is influenced by plant structure, nutritive value and availability of vegetation, dry matter and nutrient requirements of the animal, and intake and passage rates. When forage mass is restricted or in short supply, cattle usually spend more time grazing, and increase the number of bites per minute; however, intake per hour of grazing will usually decrease. Cattle ruminate for 5-9 hr per day, and 60-80% of rumination is done while the animal is lying down at rest. Resting occurs between periods of grazing, and during about 70% of their resting time, cattle are lying down.[7] In hot, humid conditions, cattle stand during much more of their resting time. Breeds of animal also differ in grazing behavior as affected by increasing temperature and humidity with temperate breeds terminating grazing earlier in the day than tropically adapted types.
