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In Situ Particle Size Reduction and the Effect of Particle Size on Degradation of Crude Protein and Dry Matter in the Rumen of Dairy Steers¹

Department of Dairy Science, University of Illinois, Urbana 61801

ABSTRACT

The contribution of rumen microbes to particle size reduction was examined and the influence of particle size on in situ degradation rates of crude protein and dry matter in the rumen of dairy steers fed ad libitum was determined. In addition to rumination and mastication, microbial action is of major importance in particle size reduction of some feed-stuffs in ruminants. Rates of crude protein degradation differed among feed-stuffs but were not significantly affected by particle size within feed samples. Primary and secondary rates of dry matter degradation were observed for wheat bran, linseed meal, and cottonseed meal. Soybean meal and formaldehyde-treated soybean meal data displayed only primary degradation rates for dry matter. Differences in primary rates of dry matter degradation among various particle sizes were significant only for linseed meal. Absence of a consistent pattern to the influence of particle size on rates of dry matter and crude protein degradation within a feed indicates the importance of other factors.

¹ Supported in part by the Illinois Agricultural Experiment Station and HEW PHS FD 00849.

² Department of Animal Science, University of Minnesota, St. Paul, MN 55108.