A dynamic model representing growth and senescence of forage and its intake assimilation, and utilization by the grazing ruminant is presented. Forage growth is estimated from soil moisture and fertility, solar radiation, maximal potential growth of the forage, and leaf area of green material. Forage is represented by green and dry age classes whose potential digestibility of organic matter and nitrogen decline with age at a rate characteristic of the pasture species. Animal intake is determined by the availability of forage, the animal's body weight and physiological status, and undigested food in the rumen. Food leaves the rumen by digestion and passage. Rumen digestion rate is a function of amounts of microbes and potentially digestible material in the rumen. Rumen microbial growth is determined from amount of organic matter digested and available nitrogen. Passed food and microbes are subjected to digestion in the small intestine. Digested energy and protein are summated and sequentially allocated to maintenance, pregnancy, lactation, and growth. These functions can be supported for a period by catabolism of body tissues. Outputs of the animal subsystem and the whole model show good agreement with experimental results for grazing sheep and cattle. The model has applications in research, teaching, and management.
|Original language||English (US)|
|Number of pages||8|
|State||Published - Jan 1 1974|
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