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

Rumen fermentation, duodenal digesta flow and N balance were studied in three sheep fed diets which contained urea or fishmeal as nitrogen supplement and either barley straw, barley + corn starch or molassed wheat straw (60% molasses) as carbo-hydrate source.The molar composition of rumen volatile fatty acids (VFA) with straw diets was high in acetate (64–68%), with barley diets high in propionate (32–36%) and with molasses diets high in butyrate (28–34%). Rumen ammonia concentrations (RAC) were low and constant with fishmeal diets (< 10 mM) but varied with carbohydrate source with urea diets. RAC was very high (24 mM) after feeding molasses + urea.With barley and molasses diets 73–75% of digestible dry matter (DDM) was digested in the stomach, but only 54–59% with ground and pelleted straw diets. For all diets less N passed the duodenum than was eaten. The lowest daily duodenal N passage was with molasses + urea. Daily urinary N output was highest (P < 0·01) for this diet and nitrogen balance lowest.Daily intakes of amino acids differed widely between diets but differences in duodenal passage were not so great. Molasses + urea provided the lowest values for daily duodenal amino acid flow. The amino acid content of duodenal N (mM amino acid/16 g N) was relatively constant despite broad variation between diets. Digesta alanine and valine (mM/16 g N) were higher for barley than for straw diets (P < 0·05). Digesta methionine (mM/16 g N) was lower for fishmeal than for urea diets (P < 0·01).Very little sucrose reached the duodenum with any diet.It was concluded that the form of energy-yielding nutrient inuflenced duodenal N flow by affecting ammonia-N capture in the rumen, but that the amino acid content of duodenal N was little affected. The interaction between molasses and urea was not beneficial to efficient use of urea-N in this work when molasses was the major carbohydrate component of the diet.

Interactions between dietary carbohydrate and nitrogen and digestion in sheep

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.

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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.