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Effect of Particle Size and Steam Treatment of Feedstuffs on Rate and Extent of Digestion (In Vitro and In Situ)¹

Auburn University, Auburn, AL 36849

Abstract

One in vitro ruminal fermentation and two in situ experiments were conducted to evaluate processing methods and the effect of particle size on rate and extent of nutrient disappearance from selected feeds. In Exp. 1, in vitro dry matter disappearance (DMD) was measured with corn, milo and wheat at hourly intervals for 10 h. In Exp. 2, the effect of steam treatment (2, 10 or 20 min) and particle size (2 mm and 6 mm) on DMD of corn, milo and soybean meal (SBM) at 1, 2, 4, 6, 8, 10 and 24 h was determined in situ. In Exp. 3, sized corn particles and SBM were used to determined dry matter (DM), N and starch disappearance in situ at 1, 2, 4, 6, 8, 10 and 24 h from dacron bags suspended in the rumen. In Exp. 1, DMD rates of corn and milo were not different (P<.05) and were 36% slower (P<.05) than DMD rates of wheat. In Exp. 2, 2-mm milo disappeared 19% slower (P<.05) than 2-mm corn. Steam treatment after grinding of corn did not alter DMD rate (P>.05), but it reduced (P<.05) that of 20-min-treated SBM by 25%. In exp. 3, 1-mm cracked corn disappeared faster (P<.05) than all other corn treatments. Steam treatment of 4-mm corn increased (P<.05) rate of DMD by 61%. Rates of N and starch disappearance exceeded (P< .05) those of all types of corn. Within corn, starch disappearance rate of 4-mm particles was increased (P<.05) by steam treatment but did not affect rates for smaller particles. Rate of nutrient disappearance from the dacron bags was influenced by particle size and method of processing.

¹ Journal Paper No. 4-871186 of the Alabama Agric. Exp. Sta.

² Dept. of Anim. and Dairy Sci. and Alabama Agric. Exp. Sta.

³ Current address: International Minerals and Chemical Corp., 2621 East Camelback, Suite 135, Phoenix, AZ 85016.