Starch utilization by ruminants: from basics to the bunk.

Abstract

Starch is the major energy component of grains. Wheat contains 77% of DM as starch, corn and sorghum contain 72%, and barley and oats contain 57 to 58%. In vitro systems have provided valuable data on kinetic aspects of starch digestion. Molecular biological techniques have provided a clearer picture of the ruminal microbial milieu. Proportions of starch fermented in the rumen can be predicted satisfactorily for a variety of grains and processing methods. Compared with dry rolling, steam processing (flaking or rolling) increases ruminal digestibility of starch (percentage of intake) from 52 to 78% for sorghum, from 75 to 85% for corn, and six percentage units or less for other grains. Recent research provides new insight into pancreatic function and intestinal glucose transport systems. The capacity to digest starch in the intestine ranges from 45 to 85% of starch entering the duodenum, with that capacity apparently limited by the supply of pancreatic amylase. There is evidence that amylase secretion may be enhanced by increasing duodenal entry of protein. Capacity for active transport of glucose across of gut wall does not seem to limit the amount of starch digested that is absorbed as glucose. For ruminants eating medium- to high-concentrate diets, about 30% of their total glucose need comes from glucose absorption, 50% from organic acid absorption (substrates for hepatic gluconeogenesis), and 20% from other sources. When glucose absorption from the gut increases, ruminants generally adjust (decrease) gluconeogenesis to meet their need; that need is directly linked to DE intake. In terms of overall ME yield, grain starch is best used when it is fermented in the rumen. However, close coordination of protein and starch supply to the duodenum may improve capture of starch in the form of glucose.

Colostrum production in ewes: a review of regulation mechanisms and of energy supply

“…The amount of starch that is digested in the rumen, or that escapes the rumen and passes to the lower gastrointestinal tract, will vary with the physiological state of the animal, as well as the type of grain and the physical and chemical processing of the grain (Nocek and Tamminga, 1991;Huntington, 1997). Within a grain type, physical processing generally increases the rate of starch digestion in the rumen by breaking down the outer coat of the kernel, giving the enzymes secreted by rumen microbes access to the starch.…”

“…The starch in similarly processed wheat, oats and barley is generally more fermentable in the rumen than the starch in corn (Nocek and Tamminga, 1991). In fact, 20% of starch is delivered post-ruminally in dry-rolled corn and sorghum, compared with 14% for barley and 5% for oats (Huntington, 1997). Thus, when Knowlton et al (1998) fed cows with dryground corn, starch digestibility increased, as did milk production, but much of the increase in starch digestion was due to an increased disappearance of starch from the large intestine rather than an increase in digestion in the rumen or the small intestine.…”

“…Thus, Taniguchi et al, (1993) reported an increase in the digestibility of starch in the small intestine of sheep in direct response to an increased supply of protein to this organ. With more protein available for digestion in the small intestine there is probably greater secretion of pancreatic enzymes, including those responsible for starch digestion (Huntington, 1997). Therefore, when a large amount of starch is used for supplementation, we recommend the use of 20% to 25% more protein than the National Research Council (1985) recommendation (Banchero et al, 2004a).…”

Effect of grain type and processing method on rumen fermentation and milk rumenic acid production

“…It is well established that barley starch is more rapidly and completely degraded in the rumen compared with corn starch (Ørskov, 1986;Huntington, 1997). Furthermore, rumen availability and degradability of grain starch can be increased by processing grain (Hale, 1973;Theurer, 1986).…”

“…It was hypothesized that a rapidly fermentable starch source (barley) would inhibit the reduction of t11-18:1 to 18:0 to a greater extent resulting in greater concentrations of t11-18:1 in rumen and milk RA compared with a less fermentable starch source (corn) (Ørskov, 1986;Huntington, 1997). A reduction in grain particle size by grinding could increase starch availability and degradability for ground diets compared with rolled diets.…”