Starch utilization may be markedly enhanced by proper grain processing; however, extent of improvement is primarily dependent upon the ruminant species, grain source and method of processing. Grain processing has less impact on starch digestion by sheep than cattle. The magnitude of improvement is inverse to the starch digestion values for nonprocessed (or minimally processed) grains. Utilization of sorghum grain starch is improved most by extensive processing, and then corn, with little improvement in barley starch digestion. Studies comparing processing effects on barley or wheat starch utilization by cattle were not found. Steam-flaking consistently improves digestibility of starch by cattle fed corn- or sorghum grain-based diets over whole, ground or dry-rolled processes. Other extensive processing methods appear to enhance starch digestibility of corn and sorghum grain to a similar extent as steam-flaking, but comparative data are too limited to quantitate adequately effects of these methods. This improvement in starch utilization appears to be the primary reason for enhanced feed conversion of cattle fed diets high in these processed grains. The major site of cereal grain starch digestion is usually the rumen. Processing increases microbial degradation of starch in the rumen and decreases amounts of starch digested post-ruminally. Rates of in vitro amylolytic attack of starch in cereal grains by both ruminal microbial and pancreatic enzyme sources are improved by processing methods employing proper combinations of moisture, heat and pressure. In vitro and in situ studies suggest that much of the increase in ruminal starch fermentation with steam-flaking is due to changes in starch granular structure, which produces additive effects beyond those of decreasing particle size. Thus, efficiency of ruminal starch fermentation by cattle appears to be improved by proper processing of corn and sorghum grain. Processing and grain source studies both suggest that maximal total tract starch digestibility is positively related to the extent of digestion in the rumen.

Grain processing effects on starch utilization by ruminants.

1. In one experiment the effect on rumen pH of feeding with restricted amounts of whole or pelleted barley was studied. With whole barley there was little variation in rumen pH associated with feeding time, but with pelleted barley the pH decreased from about 7-0 before feeding to about 5-3, 2--3 h after feeding. 2. The rate of disappearance of dried grass during incubation in the rumens of sheep receiving either whole or pelleted barley was studied in a second experiment. After 24 h incubation only 423 mg/g incubated had disappeared in the rumen of sheep receiving pelleted barley while 625 mg/g incubated had disappeared when it was incubated in the rumen of sheep receiving whole barley. 3. The voluntary intake of dried grass of lambs was studied in a third experiment when they received supplements of either 25 or 50 g whole or pelleted barley/kg live weight 0-75. At the high level, pelleted barley reduced intake of dried grass by 534 g/kg but whole barley reduced it by only 352 g/kg. The digestibility of acid-detergent fibre was reduced more by pelleted barley than by whole barley but there was a tendency for a small increase in digestibility of the barley due to processing. 4. The implications of these findings on supplementation of roughages with cereals are discussed.

/pdf/the-effects-of-processing-of-barley-based-supplements-on-3b0xfoq1jp.pdf

The effects of processing of barley-based supplements on rumen pH, rate of digestion of voluntary intake of dried grass in sheep.

Digestion and Absorption in the Hindgut of Ruminants

The effect of rumen ammonia concentration on microbial protein synthesis and fermentation was studied in three separate experiments. In each experiment three separate sheep were fed semi-purified diets [designated A (‘concentrate’), B (‘roughageconcentrate’) or C (‘roughage’)] and infused intra-ruminally with five graded amounts of urea according to a randomised block design. Rumen ammonia concentrations remained low until the total nitrogen intake was about 10 g day−1 after which rumen ammonia concentration rose rapidly. Rumen and duodenal ammonia concentrations were linearly related (r=0.90, 0.98 and 0.84 for diets A, B and C, respectively; P< 0.001). Microbial protein production did not increase when rumen ammonia concentrations exceeded 2.8 mM for diet A, 6.0 mM for diet B and 1.6 mM for diet C. Diets A and C produced a propionate-type fermentation while diet B was characterised by an acetate-type fermentation. Rumen ammonia concentration had no apparent effect on either concentration or the molar proportions of volatile fatty acids. There were no systematic trends in digestibility in relation to rumen ammonia concentration.

Ammonia concentration and protein synthesis in the rumen

Technical developments have allowed large numbers of measurements of the extent of digestion and synthesis in the rumen to be made in the past 20 y. The vast majority have been obtained from sheep fed at intakes close to maintenance. Attention has tended to be focussed on high-forage diets and these have often been offered in several small meals over the day in order to reduce technical problems of measuring digestion.

Digestion and end-product formation in the rumen from production rations

I . Using shccp fitted with re-entrant cannulas in the proximal duodenum, and which were given a ration containing long straw, a series of three experiments was conducted in which the flow of digcsta to the duodenum was measured and sampled continuously for 3 d. Therc appeared to be no consistent effect of this procedure on total flow of digesta to the duodenum from day to day, indicating that under our conditions a 24 h pattern of flow can bc taken as representative of digesta entering the duodenum. 2. In a further series of four experiments, each lasting 3 d, rations identical in composition to that given in the first series of experiments, but differing in the physical form of the roughage component (chopped or ground), were given to the sheep. There was no consistent effect of altering the particle size of the roughage component of the diet on total daily flow of digesta, or in the dry-matter content of the digesta entering the duodenum. 3. Significantly ( P < 0-01) more starch entered the duodenum per day when the ration included long or chopped straw than when it contained ground straw; all rations contained ground maize. 4. A peak in the flow of digesta, dry matter and starch to the duodenurn occurrcd between 4 and 12 h after feeding the shcep.

/pdf/the-flow-of-digesta-dry-matter-and-starch-to-the-duodenum-in-1c1k7t44nj.pdf

The flow of digesta, dry matter and starch to the duodenum in sheep given rations containing straw of varying particle size.

1. The effect of feeding sheep at two different frequencies (once hourly and once daily) on the flow of digesta, dry matter, and starch to the duodenum was assessed by fitting sheep with re-entrant cannulas in the proximal duodenum and giving them, at each feeding frequency, rations differing in the particle size of the roughage component. 2. Frequent feeding resulted in a less variable daily pattern of flow of digesta and a significant increase (P < 0·01) in the total daily volume flowing to the duodenum. Altering the particle size of the ration did not affect the flow of digesta at either feeding frequency. 3. The pattern of flow of dry matter followed very closely that of the flow of digesta, but there was a significant (P < 0·001) interaction between feeding frequency and particle size of the ration which affected the flow of starch to the duodenum. As a result, more starch entered the duodenum when both the frequency of feeding and the particle size of the ration were increased.

/pdf/the-effect-of-frequency-of-feeding-on-the-flow-and-1xmxy4cg4a.pdf

The effect of frequency of feeding on the flow and composition of duodenal digesta in sheep given straw-based diets.

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The flow of digesta, dry matter and starch to the duodenum in sheep given rations containing straw of varying particle size.

The effect of frequency of feeding on the flow and composition of duodenal digesta in sheep given straw-based diets.