Effects of varying particle size of forage on digestion and chewing behavior of dairy heifers.

Eighteen Holstein heifers were fed long and chopped coarse and fine alfalfa hay ad libitum to evaluate effects of physical form on digestion and chemical composition of feed and fecal particles and to examine the applicability of a sinusoidal model to chewing behavior. Recordings of jaw movement were divided into 1-h segments for analysis. Least square mean size of fecal particles from coarse and finely chopped diets were 290 and 297 micrometers as compared to 227 micrometers on long hay. Intakes of dry matter were greater an digestibilities lower for chopped as compared to long hay. Crude protein content of separated feed and fecal particles increased as particle size decreased. Neural and acid detergent fiber concentrations decreased in feed and feces with decreasing particle size. Lignin content of feed particles decreased as particle size decreased, whereas for fecal particles lignin as a percent of cell wall followed a "U" shaped pattern of declining then increasing as size decreased. Patterns were sinusoidal for eating and ruminating long and chopped hays and total chewing (eating and ruminating) of long hay. Our results suggest a gradual effect on chemical degradation and physical detrition of digesta particles and chewing behavior as forage particle size decreased.