Limits to starch digestion in the ruminant small intestine

Site and extent of starch digestion by ruminant animals varies with species, grain type and processing method. Based on a review of 40 different experiments with cattle, between 18 and 42% of the dietary starch from corn and sorghum grains fed to cattle reaches the small intestine for digestion. With more extensive grain processing, a smaller quantity of starch reaches the small intestine. In the small intestine, from 47 to 88% of the presented starch is digested, while in the large intestine, 33 to 62% of the presented starch is digested. Though limits to digestion in and absorption from the small intestine can be demonstrated by infusing starch and glucose into the duodenum, enzymatic capacity does not appear to limit intestinal starch digestion since no plateau in the amount of starch disappearing from the small intestine is detected with typical diets. Yet, extent of digestion is incomplete. Other factors, such as time and surface exposure may limit small intestinal digestion of starch. Processing methods to reduce particle size or alter the protein matrix, which cements starch granules together, will increase the extent of digestion both in the rumen and in the small intestine. Performance data from growing cattle fed processed corn and sorghum grains indicate that starch was used 42% more efficiently if it was digested in the small intestine rather than in the rumen. Though total tract starch digestibility is of primary concern, results support the concept that energetic efficiency of growing ruminants is greater if starch is digested in the small intestine rather than in the rumen.     

Nutritional benefits of specialty grain hybrids in beef feedlot diets

The study of grain hybrids with faster or more extensive rates of ruminal starch fermentation has been a key research area. Because grain sorghum starch is generally regarded as less accessible to enzymatic degradation than starch in other grains, it has received the greatest research emphasis. However, all grains have been evaluated to some extent. Grain sorghum hybrids appear to be more variable in digestibility, in vitro and in vivo, and in rate of starch fermentation than are corn hybrids. The greater variation may be partially because grain sorghum hybrids are developed and evaluated under more stressful environmental conditions (high temperature and limited water conditions) than are corn hybrids. In vitro and in vivo studies indicate that differences in grain hybrids exist, but these differences may not totally explain differences in cattle performance. The response to feeding high-lysine corn to cattle has been variable. Although high-lysine corn supplies more lysine in the diet, lysine flow to the abomasum was not increased. Hybrids selected for increased lysine content have been shown to have faster in vitro rates of starch digestion, suggesting that improvements in animal performance may be related to the indirect selection for improved energy utilization. In one study in which high-oil corn was evaluated, feed conversion was not improved compared with a control corn diet. At the present time additional studies in which other genetic modifications of grain hybrids are evaluated are in progress, but the results have not been published.     

Factors affecting starch digestibility with special emphasis on sorghum and corn

Starch exists inside the endosperm of cereals enmeshed in a protein matrix, which is particularly strong in sorghum and corn. Starch digestibility is affected by the plant species, the extent of starch-protein interaction, the physical form of the granule, inhibitors such as tannins, and the type of starch. Among the cereals, sorghum generally has the lowest starch digestibility. The resistance to digestive action of the hard peripheral endosperm layer is largely responsible for this effect. Processing methods such as steam-flaking and reconstitution are effective in raising sorghum digestibility to near that of corn. Waxy sorghum shows consistently higher feeding value than normal sorghum. Both the starch granules and the protein matrix around them are more digestible in waxy grain. The development of new heterowaxy or waxy sorghum hybrids may further increase sorghum feed efficiency.     

蒸汽压片玉米调控瘤胃发酵与营养物质消化的研究进展

玉米作为反刍动物重要能量饲料,在饲养实践中通常需要进行一定加工处理之后进行饲喂,以提高其养分利用率.蒸汽压片技术是目前一种重要的玉米加工方式,可以显著提高玉米淀粉全消化道消化率,并在维持瘤胃微生物正常发酵方面具有重要作用.本文综述了蒸汽压片玉米调控瘤胃中营养物质消化和微生物发酵的作用功效与机理,以期为蒸汽压片玉米的进一...     

Effects of barley grain processing on the site and extent of digestion of beef feedlot finishing diets

Effects of extent of barley rolling on chewing activities, ruminal fermentation, and site and extent of digestion were evaluated for feedlot finishing cattle diets in a 4 x 4 Latin square design. Four Jersey steers (452 kg), cannulated in the rumen and duodenum, were used. Barley grain was temper-rolled to four extents: coarse, medium, medium-flat, and flat, which were expressed as processing index (PI, volume weight of barley after processing expressed as a percentage of its volume weight before processing, DM basis) and equivalent to 82, 75, 70, and 65%, respectively. Diets consisted of 9.7% barley silage, 86% temper-rolled barley, and 4.3% other ingredients (DM basis). Steers were offered ad libitum access to a total mixed ration once daily. Dry matter intake was not affected (P > 0.15) by PI of barley. Digestibility of OM in the rumen and in the total tract were numerically lower (P = 0.13) for steers fed coarsely rolled barley than for steers fed more extensively processed barley. Digestibility of starch in the total tract was linearly increased (P = 0.02) with grain processing, but NDF digestion was not affected by processing (P > 0.15). Digestibility of CP did not differ in the rumen but tended (P = 0.08) to increase in the total tract with increased processing of barley. Flow of microbial nitrogen to the duodenum was approximately one-third lower (linear effect, P = 0.06) for steers fed coarsely rolled barley than for steers fed further rolled barley. Increased grain processing tended to decrease (linear effect, P = 0.08) rumination time without affecting eating time. These results indicate that optimal degree of rolling for barley fed to feedlot cattle corresponded to a PI of 75% or lower. Coarsely rolled barley is not recommended because it resulted in the lowest digestibility and lowest microbial protein synthesis. Processing barley to attain a PI less than 75% resulted in marginal improvements in feed digestion, but rumination time decreased, which could lead to problems associated with acidosis if lower-fiber diets are used.     

Effect of sorghum grain variety and reconstitution on site and extent of starch and protein digestion in steers

Hetero-yellow (HY), red (RED) and brown (BR, high tannin) sorghums were fed dry-rolled or reconstituted (RED and BR only) to evaluate the effect of variety and reconstitution on the site and extent of starch and protein digestion in steers fitted with ruminal, duodenal and ileal cannulae. Processed grains were incorporated into 88% sorghum (DM basis) diets fed at 2% of body weight in a 5 X 5 Latin square. Ruminal fermentation of organic matter, starch and protein tended to be lower for the dry-rolled RED than for either the dry-rolled HY or BR sorghum. Digestion of organic matter (OM) and starch in the small intestine was very low for dry-rolled sorghums. Total tract starch digestibility was lower for the dry-rolled RED sorghum (86.9%) than the BR (90.8%) and HY (91.4%). Nitrogen (N) digestibility ranged from 53.1% for the dry-rolled BR to 64.5% for the HY. Tannins were extensively (95.2%) degraded in the rumen, which may have enhanced fermentation of the BR sorghum. Reconstitution increased (P less than .05) total-tract starch digestion of the RED and tended to increase starch digestion of the BR as well. Total N flow to the duodenum tended to increase with reconstitution, with most of the increase being due to greater (P less than .05) microbial-N. Reconstitution also increased (P less than .05) total-tract N digestibility of the RED. The response to reconstitution for the RED sorghum appeared to be due primarily to an increase (P less than .10) in the extent of fermentation of organic matter and starch in the rumen. Reconstitution of BR, however, enhanced disappearance of starch from the small intestine. In both cases, most (97.3%) of the digestible starch of the reconstituted sorghums had disappeared before the terminal ileum. In contrast, 14.5% (621 g) of the digestible starch of dry-rolled RED disappeared in the large intestine. Sorghum grain variety and reconstitution appear to alter site and extent of starch and protein digestion, which may result in variable performance of cattle fed sorghum grain diets.     

6种常用饲料原料在肉牛瘤胃内降解规律的研究

选用3头体重相近的安装有永久性瘤胃瘘管的科尔沁肉牛,采用尼龙袋法测定玉米面、压片玉米、啤酒糟、玉米酒糟、蚕豆和豌豆壳6种饲料原料在肉牛瘤胃内干物质(DM)、粗蛋白(CP)、淀粉的瘤胃降解率。结果显示:6种饲料原料的DM、CP的肉牛瘤胃有效降解率,压片玉米与玉米面显著高于蚕豆、豌豆壳、玉米酒糟和啤酒糟(P<0.05),压片玉米与玉米面差异不显著(P>0.05);淀粉的肉牛瘤胃有效降解率大小顺序依次为蚕豆、压片玉米、玉米面、豌豆壳、玉米酒糟和啤酒糟。试验表明,蚕豆和压片玉米、玉米面的瘤胃降解率较高,玉米酒糟与豌豆壳居中,啤酒糟相对较差。     

Effect of grain processing degree on intake, digestion, ruminal fermentation, and performance characteristics of steers fed medium-concentrate growing diets

Three trials were conducted to evaluate the effects of degree of barley and corn processing on performance and digestion characteristics of steers fed growing diets. Trial 1 used 14 (328 +/- 43 kg initial BW) Holstein steers fitted with ruminal, duodenal, and ileal cannulas in a completely randomized design to evaluate intake, site of digestion, and ruminal fermentation. Treatments consisted of coarsely rolled barley (2,770 microm), moderately rolled barley (2,127 microm), and finely rolled barley (1,385 microm). Trial 2 used 141 crossbred beef steers (319 +/- 5.5 kg initial BW; 441 +/- 5.5 kg final BW) fed for 84 d in a 2 x 2 factorial arrangement to evaluate the effects of grain source (barley or corn) and extent of processing (coarse or fine) on steer performance. Trial 3 investigated four degrees of grain processing in barley-based growing diets and used 143 crossbred steers (277 +/- 19 kg initial BW; 396 +/- 19 kg final BW) fed for 93 d. Treatments were coarsely, moderately, and finely rolled barley and a mixture of coarsely and finely rolled barley to approximate moderately rolled barley. In Trial 1, total tract digestibilities of OM, CP, NDF, and ADF were not affected (P > or = 0.10) by barley processing; however, total tract starch digestibility increased linearly (P < 0.05), and fecal starch output decreased linearly (P < 0.05) with finer barley processing. In situ DM, CP, starch disappearance rate, starch soluble fraction, and extent of starch digestion increased linearly (P < 0.05) with finer processing. In Trial 2, final BW and ADG were not affected by degree of processing or type of grain (P > or = 0.13). Steers fed corn had greater DMI (P = 0.05) than those fed barley. In Trial 3, DMI decreased linearly with finer degree of processing (P = 0.003). Gain efficiency, apparent dietary NEm, and apparent dietary NEg increased (P < 0.001) with increased degree of processing. Finer processing of barley improved characteristics of starch digestion and feed efficiency, but finer processing of corn did not improve animal performance in medium-concentrate, growing diets.     

Combinations of high-moisture harvested sorghum grain and dry-rolled corn: effects on site and extent of digestion in beef heifers

To determine the effects of blends of high-moisture harvested sorghum grain (HMS) and dry-rolled corn (DRC) on site and extent of digestion, high-grain diets were fed to Angus-Hereford heifers (315 kg) in a 5 x 5 latin square. The grain portion consisted of ratios (HMS:DRC) of 0:100, 25:75, 50:50, 75:25 and 100:0. Heifers were equipped with ruminal, duodenal and ileal T-type cannulas. Digestibilities of OM (P less than .05) and non-ammonia nitrogen (NAN; P less than .01) in the total tract declined linearly as HMS replaced DRC. Chyme flow (liters/d) through the duodenum increased linearly (P less than .01), and true ruminal OM disappearance tended to decline linearly (P less than .10) as HMS replaced DRC. A quadratic response (P less than .05) in extent of starch disappearance (g/d) in the rumen was noted; blends were lower than either individual grain. Ruminal escape of feed N tended to be quadratic (P less than .10); values for individual grain types were greater than blends. Microbial efficiency increased linearly (P less than .05) as HMS replaced DRC. Extent of starch digestion in the rumen averaged 82.7% compared to only 2.9% in the small intestine and 5.7% in the large intestine. Altering the ratio of HMS to DRC appeared to have more effect on ruminal fermentation than on digestion in the small intestine; most starch and nitrogen responses were quadratic. Increases in ruminal pH and chyme flow, potentially caused by increased salivary flow, may cause non-linear changes in the solubility of proteins in HMS and DRC, when fed as blends, altering the digestibility of protein and starch from values predicted from the individual grains.     

Recent information on processing of grain for ruminants

When excessively processed cereals are given to ruminants a vast surface area of highly fermentable substrate is exposed to the rumen microorganisms. The subsequent effect on digestion and metabolism will depend largely on whether the cereal based diets are fed as the main or sole part of the diet or whether they are given as supplements to roughage based diets.Given as sole feeds, excessively processed grains can give rise to alterations in carcass quality (soft fat) in lambs, and problems of acidosis and rumenitis.Given as supplements to diets based on roughage, excessively processed grains can seriously reduce the rate of cellulose digestion with a consequent decrease in roughage intake and digestibility.The optimum extent of processing appears to be the minimum required to avoid an unacceptably low digestibility. The processing required is different for small ruminants (e.g. sheep, goats and calves) than for large (e.g. cattle).For sheep, grain should be fed whole; in general, processing does not increase digestibility or food utilization and can result in depressed cellulose digestion and in soft fat.For cattle some processing is required to ensure adequate digestion but the optimum is that required to give entrance through the seed coats to microorganisms and digestive enzymes. New methods, such as chemical treatment of whole grain, have given promising results.     

蒸汽压片玉米加工工艺及其在肉牛生产中应用的研究进展

玉米是肉牛生产中的主要能量饲料,蒸汽压片处理可以提高玉米的淀粉消化率,并对玉米的淀粉糊化度和能值等产生一定影响,对肉牛的瘤胃发酵模式、生产性能、牛肉品质及其经济效益有积极的影响。本文综述了蒸汽压片技术、经蒸汽压片处理后玉米营养价值的变化以及饲喂蒸汽压片玉米对肉牛生产性能及肉品质影响等方面的研究进展,以期为蒸汽压片玉米在肉牛生产中的进一步推广应用提供参考。     

Comparison of corn with four sorghum grain hybrids: site and extent of digestion in steers

Four diverse sorghum hybrids (yellow, cream, hetero-yellow and red) and corn grain were dry-rolled and fed in an 85% grain diet to Angus-Hereford steers (241 kg) equipped with ruminal and double L-type duodenal and ileal cannulas to compare the effects of grain source on site and extent of digestion. Yellow (yel) has a homozygous yellow endosperm, with a yellow seed coat, whereas cream and hetero-yellow (het-yel) have a heterozygous yellow endosperm with white and red seed coats, respectively. Red has a homozygous white endosperm with a red seed coat. Diets were fed at 2% of initial BW (DM basis) in a 5 x 5 Latin square. Total digestive tract starch digestibility (%) was greater (P less than .05) for corn (92.5) than for red (84.3), yel (84.3) and het-yel (82.9) but not greater (P greater than .10) than for cream (87.9). Ruminal starch digestibility (%) was greater (P less than .10) for corn (85.8) than for sorghum hybrids (69.1). Pre-cecal starch digestibility (%) was greater (P less than .05) for corn (90.6) than for het-yel (76.2), red (74.8) and yel (74.1). Ruminal escape (%) of grain N was greater (P less than .10) for red (79.9) than for het-yel (69.2), cream (66.5) and yel (66.1), with corn (53.6) being less (P less than .10) than sorghum hybrids. Pre-cecal and total tract non-NH3 N digestibilities (%) were not altered (P greater than .10) by grain source. Hybrid of sorghum altered site and extent of starch digestion and ruminal escape of grain N; hybrids had estimated gain:feed ratios that were 81 to 93% of those of rolled corn grain.     

Processing of corn and sorghum for feedlot cattle.

Approximately 75% to 80% of expenses involved in cattle feeding in commercial feedlots are feed costs. Grains are used in feedlot diets to improve the performance and efficiency of feedlot cattle by increasing the energy density of diets. Grains for these diets are commonly processed for various reasons, including improving palatability, altering particle size, increasing digestibility, altering the rate, site, and extent of digestion, and facilitating preservation or storage. Altering the rate, site, and extent of digestion in turn can alter cattle performance. This article focuses on processing methods common to feedlots and the primary grains fed, corn and grain sorghum.     

Steam-processed corn and sorghum grain flaked at different densities alter ruminal, small intestinal, and total tract digestibility of starch by steers.

Crossbred steers (n = 7; 400 kg BW), fitted with T-type cannulas in the duodenum and ileum, were used to examine the effects of processing method, dry-rolled (DR) vs. steam-flaked (SF) sorghum grain, and degree of processing (flake density; FD) of SF corn (SFC) and SF sorghum (SFS) grain on site and extent of DM, starch, and N digestibilities and to measure extent of microbial N flow to the duodenum. In Exp. 1, diets contained 77% DRS or 77% SFS with FD of 437, 360, and 283 g/L (SF34, SF28, and SF22). In Exp. 2, diets contained 77% SFC with FD of SF34 or SF22. For sorghum and corn diets, respective average daily intakes were as follows: DM, 6.7 and 8.1 kg; starch, 3.8 and 4.7 kg; N, 136 and 149 g. Steers fed SFS vs. DRS increased (P = .01) starch digestibilities (percentage of intake) in the rumen (82 vs. 67%) and total tract (98.9 vs. 96.5%) and decreased digestibilities in the small intestine (16 vs. 28%; P = .01) and large intestine (.5 vs 1.2%; P = .05). As a percentage of starch entering the segment, digestibility was increased (P = .01) within the small intestine (91 vs. 85%) but was not altered within the large intestine by steers fed SFS vs. DRS. Decreasing FD of SFS and of SFC, respectively, linearly increased starch digestibilities (percentage of intake) in the rumen (P = .03, .02) and total tract (P = .03, .09) and linearly diminished starch digestibilities in the small intestine (P = .04, .09). Starch digestibilities (percentage of entry) within the small or large intestine were not changed by FD. The percentage of dietary corn or sorghum starch digested in the large intestine was very small, less than 2% of intake. Microbial N flow to the duodenum was not altered by SFS compared to DRS, or by decreasing FD of SFS and SFC. Reducing FD of SFS, but not of SFC, tended to decrease (P = .07) microbial efficiency linearly and tended to increase (P = .06) total tract N digestibilities linearly. Steam flaking compared to dry rolling of sorghum grain and decreasing FD of SFC and SFS grain consistently increased starch digestibility in the rumen and total tract of growing steers. The greatest total digestibility of dietary starch occurred when the proportion digested in the rumen was maximized and the fraction digested in the small intestine was minimized. These changes in sites of digestion account, in part, for the improved N conservation and greater hepatic output of glucose by steers fed lower FD of SFS reported in our companion papers.     

Influence of dry-rolling and tempering agent addition during the steam-flaking of sorghum grain on its feeding value for feedlot cattle

Two experiments were conducted to evaluate the influence of dry-rolling (DRS) and tempering agent (TA) addition during the steam-flaking of grain sorghum (SFS) for feedlot cattle. Five dietary treatments were compared: 1) DRS; 2) SFS, no TA; 3) SFS, 0.275 mg/kg of TA; 4) SFS, 1.375 mg/kg of TA; and 5) SFS, 2.750 mg/kg of TA. Bulk densities of DRS and SFS were 0.48 and 0.36 kg/L, respectively. Diets contained 70.6% grain sorghum (DM basis). One hundred fifty crossbred steers (336 kg of BW) were used in a 115-d finishing experiment to evaluate treatment effects on feedlot performance. Body weight gain averaged 1.49 kg/d and was not affected (P = 0.47) by treatments. The SFS reduced (P < 0.01) DMI (9%) and enhanced (P < 0.01) G:F (13%) and the NE(m) and NE(g) value of the diet (9 and 11%, respectively). Use of a TA before flaking sorghum did not influence (P > 0.20) cattle growth performance or NE(m) or NE(g) value of the diet. Given that the NE(m) and NE(g) values of DRS are 2.00 and 1.35 Mcal/kg, respectively (NRC, 1996), the corresponding values for SFS were 2.28 and 1.59 Mcal/kg. Five steers (397 kg of BW) with ruminal and duodenal cannulas were used in a 5 x 5 Latin square design to evaluate treatment effects on digestive function. Ruminal digestion of OM and starch was greater (14 and 16%, respectively; P < 0.01) for SFS vs. DRS. Steam-flaking sorghum increased (P < 0.01) postruminal digestion of OM (11%), N (10%), and starch (25%) and total tract digestion (P < 0.01) of OM (8.3%), N (8.2%), and starch (8.9%). Grain processing did not affect (P > 0.20) ruminal pH or VFA molar proportions. There was a cubic component (P < 0.10) to level of TA on ruminal pH and VFA molar proportions, with values being optimal at 1.375 mg/kg of tempering agent. It is concluded that steam-flaking grain sorghum will increase its NE value for maintenance and gain (14 and 18%, respectively) and enhance the MP value of the diet due to greater intestinal N digestion. The use of a TA to enhance the mechanical efficiency of the flaking process may not otherwise benefit the feeding value of sorghum.     

Selection of a sterilization method for the study of cereal grain digestion

Experiments were initiated to select a sterilization method(s) that minimizes alterations in the digestive properties of cereal grains and, thus, would be suitable for the study of cereal grain digestion by pure cultures of ruminal bacteria. The following five treatments were examined: unsterilized (U), autoclaving with buffer (AB), autoclaving without buffer (AD), ethylene oxide (E), and gamma irradiation (I). Solubility of DM, starch, and CP was determined by soaking grain in buffer for 1 h followed by filtration through Whatman #54 filter paper. Ground corn and wheat from each treatment were placed in vials with a 1:1 mixture of Bryant's medium and ruminal inoculum. Vials were incubated for 4, 8, 12, 24, and 48 h and analyzed for starch content. Bacterial growth was not evident in sterilized, uninoculated samples. The AD treatment decreased the disappearance of CP in wheat and corn, whereas AB caused an increase in the disappearance of DM, CP, and starch in wheat (P less than .001) compared with U. Rates of microbial starch digestion for corn were 1.3, 1.5, 3.3, 14.7, and 3.5%/h and for wheat were 1.3, 3.4, 4.6, 17.1, and 4.6%/h for AD, E, I, AB, and U, respectively. Contrasts indicated that AD and AB differed (P less than .001) from U for both corn and wheat. It is likely that gelatinization of cereal starch enhanced microbial starch digestion in AB and the formation of Maillard products reduced starch digestion in AD. Corn and wheat sterilized with E or I had digestive properties that closely resembled those of U grain, and either sterilization method was suitable for studying cereal grain digestion.     

Increased puroindoline levels slow ruminal digestion of wheat (Triticum aestivum L.) starch by cattle

Starch is the primary nutrient in ruminant diets used to promote high levels of performance. The site of starch digestion alters the nature of digestive end products (VFA in the rumen vs. glucose in the small intestine) and the efficiency of use. Cereal grain endosperm texture plays a major role in the rate and extent of starch degradation in ruminants. Wheat grain texture is regulated by the starch surface protein complex friabilin that consists primarily of puroindoline (PIN) A and B. Soft kernel texture in wheat is a result of both PIN genes being in the wild type active form and bound to starch. The objective of this study was to investigate the effect of varying PIN content in wheat on the rate of starch digestion in the rumen of beef cattle. In Exp. 1, 6 transgenic soft pin a/b isolines created in a hard wheat background, and 2 hard wheat controls were milled to yield a wide range of mean particle sizes across all lines. Milled samples were incubated in situ for 3 h. Increased expression of both PINA and PINB decreased DM digestibility (DMD) by 29.2% (P < 0.05) and decreased starch digestibility by 30.8% (P < 0.05). Experiment 2 separated the effects of particle size and total PIN content on digestion by milling the hardest and softest lines such that the mean particle size was nearly identical. Increased PIN decreased DMD by 21.7% (P < 0.05) and starch digestibility by 19.9% (P < 0.05) across particle sizes smaller than whole kernel. Experiment 3 addressed the time course of PIN effects in the rumen by observing ground samples of the hardest and softest lines over a 12-h in situ period. Increased PIN decreased DMD by 10.4% (P < 0.05) and starch digestibility by 11.0% (P < 0.05) across all time points. Dry matter and starch digestibility results demonstrated that increased expression of PIN was associated with a decreased rate of ruminal digestion independent of particle size. Puroindolines seem to aid in the protection of starch molecules from microbial digestion in the rumen, potentially increasing the amount of starch entering the small intestine.     

Influence of lasalocid and monensin plus tylosin on comparative feeding value of steam-flaked versus dry-rolled corn in diets for feedlot cattle

Two trials were conducted to characterize the differences in utilization of dry-rolled and steam-flaked corn in a growing-finishing diet for feedlot cattle supplemented with and without ionophores. Ionophore treatments were: 1) no ionophore, 2) 33 mg/kg monensin sodium plus 11 mg/kg tylosin and 3) 33 mg/kg lasalocid sodium. In trial 1, treatment effects on feedlot performance were evaluated in a 239-d growing-finishing trial involving 180 crossbred steers (approximately 25% Brahman with the remainder represented by Hereford, Angus, Shorthorn and Charolais breeds in various proportions) with an average initial weight of 153 kg. In trial 2, treatment effects on characteristics of digestion were evaluated using six steers of similar breeding and background to those used in trial 1, with cannulas in the rumen and proximal duodenum. There were no interactions between corn processing and ionophore supplementation (P greater than .20). Average daily gain was not affected by steam-flaking as opposed to dry-rolling, however, feed intake was decreased 5.4% and feed conversion was improved 6.8% (P less than .01). Steam-flaking increased the estimated net energy value of the diet 7.7% and 8.5% for maintenance and gain, respectively (P less than .01). Steam-flaking increased the digestibility of starch 6.6% (P less than .01). Steam-flaking increased ruminal molar concentrations of propionate and decreased acetate:propionate ratio and estimated methane production (P less than .10). Both monensin-tylosin and lasalocid resulted in reduced feed intake (12.3 and 6.5%, respectively, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Flaking corn: processing mechanics,quality standards,and impacts on energy availability and performance of feedlot cattle

Based on performance of feedlot cattle, steam flaking increases the value of corn by 18%, considerably more than is suggested by tabular values. Tabular values underestimate the energy availability of flaked corn by failing to account for digestibility of the nonstarch OM that is increased by flaking by the same magnitude (10%) as starch. Correcting for improvement in digestibility of nonstarch OM increases the NEg value of steam-flaked corn to 1.70 Mcal/kg, a value very close to values calculated from cattle performance trials. Digestibility of starch from corn grain is limited by the protein matrix that encapsulates starch granules, and by the compact nature of the starch itself. Disruption of the protein matrix (by shear forces on hot grain during flaking) is the first limiting step toward optimizing starch digestion. Five critical production factors influence the quality of steam-flaked corn: steam chest temperature, steaming time, roll corrugation, roll gap, and roll tension. For optimal shear, it is important that rolls be hot and that kernels be hot when flaked. Steam chests should be designed to allow a steaming time of at least 30 min at maximum roller mill capacity producing a flake of 0.31 kg/L (24 lb/bushel). As little as 5% moisture uptake during steaming appears adequate. The rate of flaking and distribution of kernels across the rolls also are critical. Quality standards for steam-flaked corn include measurements of flake thickness, flake density, starch solubility, and enzyme reactivity. Flake density, the most common quality standard, closely associated with starch solubility (r2 = 0.87) and enzyme reactivity (r2 = 0.79), still explains only 63% of the variability in percentage fecal starch and 52% of the variability in starch digestibility. Direct determination of fecal starch can explain 91% of the variability in starch digestion. The NEg value of corn can be predicted from fecal starch: NEg= 1.78 - 0.0184FS. Starch digestion is a Kappa Curve function of hot flake density, reaching a maximum at a flake density of approximately 0.31 kg/L. Flaking to a density of less than 0.31 kg/L, though increasing starch solubility, may reduce DMI, increase variability of weight gain among animals within a pen, and predispose cattle to acidosis and bloat without increasing starch digestion. We recommend that the steam-flaking process be optimized on the basis of fecal starch analysis.     

Site of protein digestion in steers fed sorghum grain diets. II. Effect of grain processing methods

Seven crossbred, abomasally fistulated yearling steers (400 kg) were used in two digestion trials (crossover design) to study the effect of processing sorghum grain on the site and extent of feed and microbial protein digestion. Steers were fed an 81.5% sorghum grain diet in which the grain was either dry-rolled (DR; four steers) or steam-processed, flaked (SPF; three steers). At the end of the first trial steers were switched to the opposite treatment. Dysprosium (21 to 23 micrograms/g of feed) was used as a digesta marker. Feed, abomasal contents and fecal grab samples were collected at 12-h intervals during a 6-d total fecal collection period. Organic matter (OM) intake for SPF and DR grain diets averaged 6,426 and 6,787 g/d, respectively. Compared with DR, SPF increased (P less than .05) the apparent total digestibility and ruminal digestibility of OM. Trichloroacetic acid precipitable protein consumed by the steers was lower (P less than .05) for SPF than the DR treatment. Processing method had no effect on ruminal digestion of crude protein (CP), bacterial protein (BP) synthesis, quantity of CP entering the small intestine or on total digestion of feed protein. There was a trend for increased total and post-ruminal digestion of CP with the SPF diet. Post-ruminal digestion of BP was increased (P less than .05) by SPF grain as compared with DR. Percentage of non-BP digested ruminally, post-ruminally or in the total tract was not significantly affected by processing method.(ABSTRACT TRUNCATED AT 250 WORDS)