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Role of Particle Size and Forage Quality in Digestion and Passage by Cattle and Sheep^{1, 2,}

Missouri Cluster US Dairy-Forage Center USDA-ARS, Animal Physiology Research Unit University of Missouri, Columbia 65211

R. L. Belyea

Dairy Science Department, University of Missouri, Columbia 65211

ABSTRACT

Diminution of forage particles includes mastication, chewing, and digestion. In rumen of cattle and sheep fed all forage diets, particle size can range from 200 to over 1200 µm. Particle size reduction to about < 1200 µm must occur before passage. Dietary particle size may influence rumen particle size, but mastication and rumination minimizes differences among diets.

Ruminants expend considerable effort to move digests. Density, cell wall percentage, osmotic pressure, and pH may affect propulsion. Dense particles may sink to the bottom and resist escape. Cell wall may reduce digestion and passage. Osmotic pressure or pH may affect digestive efficiency and rhythm of intestinal tract muscles.

Chewing, exercise, physiological functions, and body size may also affect the reduction of forage particle size. More effort is necessary to chew high than low fiber diets. Young cattle (< 225 kg) lack rumination capability and body size to process forage particles efficiently. Exercised sheep (26,400 kg-m/d) ate less forage and ruminated less than controls. Other body functions, such as lactation, appear to influence chewing patterns and rumination. These relationships are poorly understood at best and need additional intensive examination.

¹ Contribution from US Department of Agriculture, Agricultural Research Service in cooperation with the University of Missouri Agricultural Experiment Station. Journal Series Number 9865.

² Mention of a trade name or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture or the University of Missouri Agriculture Experiment Station and does not imply its approval to the exclusion of other products that may also be suitable.