Processing grain to improve or shift the site of starch digestion.

Abstract

36A Processing grain to improve or shift the site of starch digestion A.F. Channon and J.B. Rowe Animal Science, University of New England, Armidale NSW 2351 achanno2@metz.une.edu.au Grain is processed to increase the digestibility and/or to manipulate the site of digestion in feedlot animals. Black (1971) suggested shifting the site of starch digestion from the rumen to the small intestine in order to minimise energy losses. In vitro assays simulating rumen fermentation and intestinal enzyme digestion (Bird et al. 1999) were used to evaluate the digestibility of the starch in rolled wheat and barley, and the effect of two levels of steam flaking. Grains were either finely/well flaked (46.5 kg/hl, 36.8 kg/hl) or coarsely/poorly flaked (56.9 kg/hl, 49.8 kg/hl). Grains were used in these processed states for the rumen fermentation assay, and were finely ground for the enzyme assay. Total acid accumulation provides the best estimate of in vitro grain fermentation (Bird et al. 1999). The well flaked grains were fermented the most extensively; these flakes were very thin and flat, providing a large surface area for microbial attachment. Despite the effects of steam flaking, the smaller surface area of the poorly flaked grains appeared to slow down microbial fermentation and these were less digested than the rolled grains. In the enzyme assay, however, digestibility of the starch was substantially greater in both the poorly and well flaked grains than in the corresponding rolled grains. Digestibilities with the enzymes of both the well flaked wheat and barley were approximately twice the digestibilities of the rolled equivalents. The fact that this assay uses a finely ground grain sample indicates that it is the starch gelatinisation and/or disruption of the protein matrix and cell structure caused by steam flaking that is more critical than available surface area in improving intestinal starch digestibility. Moderate steam flaking of grain appears to offer a means for the delivery of readily digestible starch to the small intestine with minimization of inefficient utilization in the hindgut. We acknowledge the support of Rangers Valley Feedlot, Glen Innes NSW 2370, in providing us with the milled grain samples. Bird, S.H., Rowe, J.B., Choct, M., Stachiw, S., Tyler, P., and Thompson, R.D. (1999). In vitro fermentation of grain and enzymatic digestion of cereal starch. Recent Advances in Animal Nutrition in Australia 12, 53_61. Black, J.L. (1971). A theoretical consideration of the effect of preventing rumen fermentation on the efficiency of utilization of dietary energy and protein in lambs. British Journal of Nutrition 25, 31_55. Table 1 In vitro fer mentation and enzyme digestion characteristics of processed wheat and barley. Acid (mmol) Grain Treatment Starch (% DM) Lactate Total acid pH Enzyme starch digestion (% of original)* 43.34 76.93 85.67 39.04 66.68 83.66 Wheat rolled poorly flaked well flaked 69.27 67.34 66.48 59.27 59.57 59.75 1.45 1.86 4.58 1.12 0.34 2.98 16.53 13.74 24.30 17.62 11.20 20.34 6.92 6.93 6.85 6.93 7.04 6.84 Barley rolled poorly flaked well flaked * All samples milled through a 0.5 mm sieve for assay Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)