Effect of Dietary Concentrate on In Situ Dry Matter and Nitrogen Disappearance of a Variety of Feedstuffs

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Abstract
Two ruminally cannulated steers were fed 80 or 40% concentrate diets at 1.7% of body weight (dry matter) in a crossover design. Eighteen feedstuffs (eight protein supplements, six energy feeds, and four roughages) were incubated ruminally for 4, 12, and 24 h and dry matter and nitrogen disappearance were measured. For protein supplements, correlations between soluble nitrogen (.15 N sodium chloride) and nitrogen disappearance at 4, 12, and 24 h were .82, .94, and .87. Dry matter disappearance and nitrogen disappearance for all substrates were related at 4, 12, and 24 h (correlation coefficients of .59, .80, and .57). Generally, disappearance of dry matter and nitrogen were greater for the 40 than for the 80% concentrate diet for soybean meal, cottonseed meal, and linseed meal at 12 and 24 h of incubation. Nitrogen residues at 24 h agreed reasonably well with in vivo estimates of ruminal protein escape, except for feeds such as meat meal and corn gluten meal. Predictions of ruminal protein escape were calculated based on in situ nitrogen disappearance by two equations that illustrate potential effects of feed intake and dietary concentrate.