Grain processing effects on starch utilization by ruminants

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.     

Evaluation of selected high-starch flours as ingredients in canine diets.

Cereal grains represent 30 to 60% of the DM of many companion animal diets. Once incorporated into a diet, the starch component of these grains can provide an excellent source of ME. However, crystallinity and form of starch are variable and can cause incomplete digestion within the gastrointestinal tract. Diets fed in this experiment included one of six high-starch flours as the main source of carbohydrate. The flours originated from barley, corn, potato, rice, sorghum, and wheat. The diets were extruded and kibbled. Starch fraction concentrations of flours consisted of nearly 100% rapidly digestible starch (RDS) and slowly digestible starch (SDS) combined. Starch fraction concentrations of diets paralleled concentrations in flours. Flours varied widely in concentrations of CP, fat, starch, and total dietary fiber. Ileal OM and CP digestibilities were lowest for the potato flour treatment (74 and 64%, respectively). Ileal and total tract starch digestibilities were different (P<.05) among treatments; however, the starch component of all diets was nearly completely digested (>99%). Total tract digestibility of DM and OM was lowest for sorghum (80 and 84%, respectively) compared to all other diets. Crude protein digestibility was highest for corn (87%). Wet fecal weights tended (P<.08) to be greatest for dogs fed the barley treatment (175 g/d). However, dry fecal weights (dried at 55 degrees C) were greatest for dogs consuming the sorghum diet (51 g/d). Fecal scores were consistently greater (i.e., looser stools) for the barley treatment. Any of these flours could be used without negative effects on digestion at either the ileum or in the total tract. Fecal consistency data for dogs consuming the barley treatment indicate that diets containing large amounts (>50%) of barley may not be advantageous for dog owners who house their animals indoors for most of the day.     

Effects of six carbohydrate sources on dog diet digestibility and post-prandial glucose and insulin response

The effects of six extruded diets with different starch sources (cassava flour, brewer's rice, corn, sorghum, peas or lentils) on dog total tract apparent digestibility and glycemic and insulinemic response were investigated. The experiment was carried out on thirty-six dogs with six dogs per diet in a completely randomized design. The diets containing brewer's rice and cassava flour presented the greatest digestibility of dry matter, organic matter and gross energy (p < 0.05), followed by corn and sorghum; pea and lentil diets had the lowest. Starch digestibility was greater than 98% in all diets and was greater for brewer's rice and cassava flour than for lentils and peas diets (p < 0.05). Dogs' immediate post-prandial glucose and insulin responses (AUC < or = 30 min) were greater for brewer's rice, corn, and cassava flour diets (p < 0.05), and later meal responses (AUC > or = 30 min) were greater for sorghum, lentil and pea diets (p < 0.05). Variations in diet digestibility and post-prandial response can be explained by differences in chemical composition of each starch source including fibre content and starch granule structure. The nutritional particularities of each starch ingredient can be explored through diet formulations designed to modulate glycemic response. However, more studies are required to support these.     

Simultaneous measures of rates of ruminal digestion and passage of feeds for prediction of ruminal nitrogen and dry matter digestion in lactating dairy cows

Three ruminal-cannulated Holstein cows in early lactation were fed three diets, each containing different energy and protein supplements in two consecutive 3 X 3 Latin squares. Each supplement contained a combination of three different feedstuffs (ground corn, soybean meal and wheat mids; corn gluten feed, rolled oats and distiller's dried grains; ground barley, brewer's grains and cottonseed meal). Diets consisted of 30% corn silage, 10% alfalfa hay, 10% alfalfa haylage, 17.7% ground corn plus minerals and vitamins, with the remainder as supplemental feedstuffs individually marked for measurement of ruminal turnover and in situ digestion rates. An extra period at the end of each Latin square was used to measure ruminal turnover and in situ digestion of individual forages. Diet had no effect on dry matter intake or milk yield. Mean fractional turnover (per hour) rate, measured by labeling feedstuffs with cerium, samarium or lanthanum was .044, .048, .049, .043, .047, .046, .050, .047, .049, .037, .046 and .045 for corn, soybean meal, wheat mids, corn gluten feed, oats, distiller's dried grains with solubles, barley, brewer's dried grains, cottonseed meal, alfalfa hay, corn silage and alfalfa haylage (P greater than .1), respectively. In situ-predicted ruminal degradation of N weighted for rate of passage was 61.4, 67.0, 81.5, 74.8, 86.3, 71.0, 75.7, 52.1, 54.2, 60.8, 71.7 and 70.9% for respective feedstuffs (P less than .05). In comparison with mean literature values for in vivo-measured N degradability, mean literature value = 1.172 (in situ predicted) -9.73 (P less than .05, R2 = .51). Results are interpreted to indicate a tendency for overestimating ruminal N degradability by in situ methods in feedstuffs of low degradability, while underestimating degradability in more highly degraded feedstuffs. Estimates were 11 to 17 percentage units lower than literature values for alfalfa hay and haylage and 17 units lower than literature values for distiller's dried grains.     

Effects of starch and protein sources on starch disappearance in the gastrointestinal tract of Hanwoo (Korean native) steers

Hanwoo (Korean native) steers (274.8 ± 4.6 kg) with ruminal and duodenal cannulae were used in a 4 × 4 Latin square design experiment to examine the effects of dietary treatments on starch disappearance in the gastrointestinal tract. Dietary treatments consisted of concentrate that were based on ground corn with soybean meal (C‐SBM), ground corn with corn gluten meal (C‐CGM), ground barley with soybean meal (B‐SBM) and ground barley with corn gluten meal (B‐CGM). Although the intakes of starch and protein for steers fed experimental diets were different, it did not change ruminal pH and total volatile fatty acid concentrations. Average duodenal CP flow and quantity of CP apparently digested post‐ruminally was higher (P = 0.001) for CGM‐based diets than SBM‐based diets. There were increases in quantity (P < 0.001) and percentage (P < 0.001) of corn starch digested post‐ruminally compared to barley starch. Synchronized diets showed higher percentages (P = 0.03) of starch apparently digested post‐ruminally than asynchronization. Hanwoo steers fed a corn‐based diet with a large quantity of starch reaching the duodenum and fed C‐CGM supplying great amounts of protein to the small intestine may have contributed to increased post‐ruminal starch digestion.     

Effects of six carbohydrate sources on diet digestibility and postprandial glucose and insulin responses in cats

The effects of diets with different starch sources on the total tract apparent digestibility and glucose and insulin responses in cats were investigated. Six experimental diets consisting of 35% starch were extruded, each containing one of the following ingredients: cassava flour, brewers rice, corn, sorghum, peas, or lentils. The experiment was carried out on 36 cats with 6 replications per diet in a completely randomized block design. The brewers rice diet offered greater DM, OM, and GE digestibility than the sorghum, corn, lentil, and pea diets (P < 0.05). For starch digestibility, the brewers rice diet had greater values (98.6%) than the sorghum (93.9%), lentil (95.2%), and pea (96.3%) diets (P < 0.05); however, starch digestibility was >93% for all the diets, proving that despite the low carbohydrate content of carnivorous diets, cats can efficiently digest this nutrient when it is properly processed into kibble. Mean and maximum glucose concentration and area under the glucose curve were greater for the corn-based diet than the cassava flour, sorghum, lentil, and pea diets (P < 0.05). The corn-based diets led to greater values for the mean glucose incremental concentration (10.2 mg/dL), maximum glucose incremental concentration (24.8 mg/dL), and area under the incremental glucose curve (185.5 mg.dL(-1).h(-1)) than the lentil diet (2.9 mg/dL, 3.1 mg/dL, and -40.4 mg.dL(-1).h(-1), respectively; P < 0.05). When compared with baseline values, only the corn diet stimulated an increase in the glucose response, occurring at 4 and 10 h postmeal (P < 0.05). The corn-based diet resulted in greater values for maximum incremental insulin concentration and area under the incremental insulin curve than the lentil-based diet (P < 0.05). However, plasma insulin concentrations rose in relation to the basal values for cats fed corn, sorghum, pea, and brewers rice diets (P < 0.05). Variations in diet digestibility and postprandial response can be explained by differences in the chemical composition of the starch source, including fiber content and granule structure, and also differences in the chemical compositions of the diets. The data suggest that starch has less of an effect on the cat postprandial glucose and insulin responses than on those of dogs and humans. This can be explained by the metabolic peculiarities of felines, which may slow and prolong starch digestion and absorption, leading to the delayed, less pronounced effects on their blood responses.     

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.     

鸭饲料表观代谢能和真代谢能值测定

选用80只成年北京公鸭,测定了进口鱼粉、鸭肠粉、鸭血粉、皮革粉、鸭毛粉、玉米蛋白粉、黄豆、豌豆、玉米胚芽粕、棉粕、高粱酒糟、葵花饼、芝麻粕、高粱、大麦、稻谷、次粉、米糠共计18种饲料原料的表观代谢能(AME)和真代谢能(TME),排空、收集期为36h,强饲量为50g。     

Apparent digestibility of amino acids, gross energy and starch in corn, sorghum, wheat, barley, oat groats and wheat middlings for growing pigs

Apparent nutrient digestibilities of yellow-dent corn, low-tannin sorghum, hard red winter wheat, barley, oat groats and wheat middlings were determined near the end of the small intestine and over the total digestive tract of growing pigs. Gross energy digestibilities for corn, sorghum and oat groats were similar; wheat had a slightly lower (P less than .05) digestibility, followed by barley (P less than .05), with wheat middlings being the least (P less than .05) digestible. About 7% of the gross energy in corn, sorghum, wheat and oat groats was digested in the large intestine, compared with 11% for barley and 17% for wheat middlings. The starch in all products was essentially 100% digestible by the end of the small intestine. Ileal amino acid digestibilities tended to be highest for wheat and oat groats, followed by corn, sorghum, barley and wheat middlings. The range in ileal digestibilities was 73.8 (sorghum) to 84.2% (wheat) for lysine, 69.6 (corn) to 81.4% (wheat) for tryptophan and 63.4 (wheat middlings) to 77.9% (oat groats) for threonine. Amino acid digestibilities determined over the total tract were generally higher than ileal digestibilities; however, values for lysine, methionine and phenylalanine were generally lower, indicating a net synthesis of these amino acids in the large intestine.     

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.     

Starch digestion rates in multiple samples of commonly used feed grains in diets for broiler chickens

In this study the starch digestion rates in broiler chickens from 18 samples of 5 commonly used feed grains (sorghum, wheat, maize, barley, triticale) were determined. The methodology to determine starch digestion rates in poultry is detailed herein. Starch digestion rates were not significantly different (P = 0.128) across the 18 feed grains, which reflects the wide variations that were observed within a given feedstuff. Nevertheless, starch digestion rates in broiler chickens offered wheat-based diets were significantly more rapid by 56.0% (0.117 versus 0.075 min⁻¹; P = 0.012) than their sorghum-based counterparts on the basis of a pair-wise comparison. In descending order, the following starch digestion rates were observed: wheat (0.117 min⁻¹), barley (0.104 min⁻¹), triticale (0.093 min⁻¹), maize (0.086 min⁻¹), sorghum (0.075 min⁻¹). The implications of these findings are discussed as they almost certainly have implications for poultry nutrition and the development of reduced crude protein diets for broiler chickens.     

奶牛常用饲料干物质和淀粉瘤胃降解规律的研究

以3头安装有永久性瘤胃瘘管的泌乳前期荷斯坦奶牛为试验动物，在精粗比为55：45的日粮条件下，采用Insacco法测定了奶牛常用饲料瘤胃内干物质和淀粉的降解规律。试验结果表明。不同饲料干物质和淀粉的降解率不同。能量饲料中，麸皮干物质和淀粉的瘤胃降解率高于玉米：蛋白质饲料中，干物质和淀粉的降解率由高到低顺序依次是豆粕〉胡麻饼〉棉粕：常用粗料中，玉米青贮干物质和淀粉的降解率均高于青干草。     

Barley grain for ruminants: A global treasure or tragedy

Barley grain (Hordeum vulgare L.) is characterized by a thick fibrous coat, a high level of ß-glucans and simply-arranged starch granules. World production of barley is about 30 % of that of corn. In comparison with corn, barley has more protein, methionine, lysine, cysteine and tryptophan. For ruminants, barley is the third most readily degradable cereal behind oats and wheat. Due to its more rapid starch fermentation rate compared with corn, barley also provides a more synchronous release of energy and nitrogen, thereby improving microbial nutrient assimilation. As a result, feeding barley can reduce the need for feeding protected protein sources. However, this benefit is only realized if rumen acidity is maintained within an optimal range (e.g., > 5.8 to 6.0); below this range, microbial maintenance requirements and wastage increase. With a low pH, microbial endotoxines cause pro-inflammatory responses that can weaken immunity and shorten animal longevity. Thus, mismanagement in barley processing and feeding may make a tragedy from this treasure or pearl of cereal grains. Steam-rolling of barley may improve feed efficiency and post-rumen starch digestion. However, it is doubtful if such processing can improve milk production and feed intake. Due to the need to process barley less extensively than other cereals (as long as the pericarp is broken), consistent and global standards for feeding and processing barley could be feasibly established. In high-starch diets, barley feeding reduces the need for capacious small intestinal starch assimilation, subsequently reducing hindgut starch use and fecal nutrient loss. With its nutritional exclusivities underlined, barley use will be a factual art that can either matchlessly profit or harm rumen microbes, cattle production, farm economics and the environment.     

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.     

The effects of processing barley and maize on metabolic and digestive responses in horses

The competition for customers increases the search for new grain processing methods for equine feed, but the effect on starch digestibility and metabolic responses varies. Therefore, to evaluate the effect of the processing methods, toasting and micronizing, on starch digestion and the effect on metabolic responses, the mobile bag technique (MBT) and plasma glucose and insulin concentrations in the blood were used to estimate nutrient disappearance and metabolic responses pre-cecally. Further, cecal pH, ammonium nitrogen (N), and short-chain fatty acid (SCFA) concentrations were used to estimate the metabolic response in the cecum. Four cecally cannulated horses (body weight [BW] 565 ± 35 kg) were used in a 4 × 4 Latin square design with four periods of 8 d of diet adaptation and 2 d of data collection. Diets were formulated using hay and processed grains: micronized barley (MB), toasted barley (TB), micronized maize (MM), and toasted maize (TM) and were balanced to provide 1 g starch/kg BW in the morning meal. On day 9 in each period, blood and cecal fluid samples were taken before the morning meal and hourly thereafter for 8 h. On day 10 in each period, 15 bags of either MB, TB, MM, or TM (1 × 1 × 12 cm; 15 μm pore size; 1 g feed) were placed in the stomach, respectively. The dry matter disappearance was highest for the MM at all time points compared with the other feedstuffs (P < 0.001). Maize and micronizing had the highest starch disappearance (P = 0.048) compared with barley and toasting. No treatment effect was measured for any of the glucose and insulin parameters. No feed effect was measured for the insulin parameters. Plasma glucose peaked later (P = 0.045) for maize than for barley, and TB had a larger area under the curve for glucose than MB, MM, and TM (P = 0.015). The concentration of total SCFA increased after feeding (P < 0.001), with a higher concentration for barley than for maize (P = 0.044). No treatment or feed effects were measured for ammonium N or pH, but both were affected by time (P < 0.001). In conclusion, toasting was not as efficient as micronizing to improve pre-cecal starch digestibility; therefore, the preferred processing method for both barley and maize is micronizing. Further, the amount of starch escaping enzymatical digestion in the small intestine was higher than expected.     

Estimating starch availability and protein degradation of steam-flaked and reconstituted sorghum grain through a gas production technique

Five steam-flaked sorghum grain (SFSG) samples with bulk densities of 476, 412, 347, 309 and 283 g/liter made by adjusting tension between mill rollers and three reconstituted sorghum grain (RSG) samples with reconstitution times of 10, 20 and 30 d and a control sample were analyzed for gas production kinetics (rumen liquor fermentation) and enzymatic glucose release (amyloglucosidase). Protein degradation was estimated from 6-h gas production and residual ammonia in the liquid. Gas production followed first-order kinetics (r2 greater than .98; P less than .01) and was used to describe rate and extent of digestion kinetics. Rate of gas production increased as processing degree increased. The magnitude of increase in gas production, however, was much less for RSG than for SFSG. Linear relationships were observed between enzymatic glucose release and the gas production rate constant k as well as gas production at 4,6 and 8 h (r2 greater than .98; P less than .01). Protein degradation decreased with processing degree of SFSG but increased with reconstitution time. A technique based on 6-h gas production and residual ammonia in the liquid is proposed to estimate both ruminal starch availability and ruminal protein degradability for processed sorghum grain.     

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.     

Glycemic index of cracked corn, oat groats and rolled barley in horses

Muscle glycogen synthesis depends on glucose availability. This study was undertaken to determine the glycemic and insulinemic response of horses to equal amounts of hydrolyzable carbohydrates (starch and sugar) in the form of one of three grain meals or intragastric administration of a glucose solution. In a randomized crossover design, seven horses were fed each of three grain meals (cracked corn, steamed oat groats, or rolled barley) or were infused intragastrically with glucose solution at 2 g of hydrolyzable carbohydrate (starch plus sugar) per kilogram of BW. The quantity of hydrolyzable carbohydrate ingested was not different among all treatments (P = 0.70). Plasma glucose concentration peaked in all four treatments by 1.5 to 2 h after feeding. Plasma glucose concentration remained higher than baseline in oat groats or barley-fed horses throughout 8 h, whereas plasma glucose returned to baseline by 5 to 6 h in corn-fed horses or after glucose administration. Meal consumption was slower in oat groats-fed horses than in corn-fed ones, which may confound the glycemic and insulinemic responses observed after grain feeding. Plasma glucose area under the curve (AUC) was 63% both in corn and oat groats and 57% in barley-fed horses compared with that of horses administered glucose (P = 0.13). Serum immunoreactive insulin concentration peaked between 2 and 3 h after feeding or glucose administration, and barley-fed horses had lower serum immunoreactive insulin concentration by 3 to 4 h than corn-fed horses or after glucose administration (P < 0.05). We conclude, in horses, ingestion of oat groats, corn, and barley result in similar plasma glucose AUC and, compared with the glycemic index of 100 as the glucose reference, corn, oat groats, and barley had a glycemic index of approximately 60.     

Glycemic index of starch affects nitrogen retention in grower pigs

Three studies were performed to examine the effect of starch and protein digestion rates on N retention in grower pigs. In Exp. 1, the glycemic index (GI) of corn, a malting barley, and a slow-rumen-degradable barley (SRD-barley) were measured using 6 barrows (BW = 18.0 ± 0.5 kg). The GI of malting barley was greater (P < 0.05) than that of SRD-barley (71.1 vs. 49.4), and the GI of both barley cultivars was less (P < 0.05) than that of corn (104.8). In Exp. 2, the standardized ileal digestibility of AA and DE content of the 3 ingredients were determined using 5 ileal-cannulated barrows (BW = 20.7 ± 2.3). The apparent total-tract energy digestibility values of corn (86.1%) and malting barley (85.7%) were greater (P < 0.05) than that of SRD-barley (82.3%). The standardized ileal digestibility of Lys was 94.0, 92.6, and 92.4% for corn, malting barley, and SRD-barley, respectively, and did not differ among grains. In Exp. 3, 6 diets were formulated to equal DE (3.40 Mcal/kg), standardized ileal digestibility of Lys (8.6 g/kg), starch (424.9 g/kg), and digestible CP (180.0 g/kg) using the values obtained in Exp. 2. Three GI [high (corn), medium (malting barley), and low (SRD-barley)] and 2 rates of protein digestion [rapid (soy protein hydrolysate) and slow (soy protein isolate)] were tested in a 3 × 2 factorial arrangement with 36 barrows (BW = 32.2 ± 2.5 kg). Pigs were fed 3.0 times the maintenance energy requirement daily in 2 meals for 2 wk and were housed in metabolic crates to collect feces and urine separately. At the end of the study, intestinal contents were collected from 4 equal-length segments of the small intestine. The percentage of unabsorbed CP in segment 1 relative to dietary CP was greater (P < 0.05) for the soy protein isolate diet than for the soy protein hydrolysate diet (170.3 vs. 116.5%). The percentages of unabsorbed starch in segments 1 and 2 were greater (P < 0.05) for the SRD-barley diet than for the malting barley or corn diet. Nitrogen intake and fecal N excretion were greater (P < 0.05) for pigs fed the malting barley and SRD-barley diets than for pigs fed the corn diet. Urinary N excretion was greater (P < 0.05) for pigs fed the SRD-barley diet than for pigs fed the corn or malting barley diet. Pigs fed slowly digestible starch (SRD-barley; 46.6%) had less (P < 0.05) net N retention than pigs fed corn or malting barley (54.7 and 54.1%, respectively). In conclusion, slowly digestible starch sources such as SRD-barley may not be suitable to support maximum protein deposition in restricted-fed grower pigs.     

Comparison of urea treatment with established methods of sorghum grain preservation and processing on site and extent of starch digestion by cattle.

To determine the effect of dry (D); reconstituted and ensiled (R); reconstituted and acid-treated (A); and urea-treated, high-moisture (U) sorghum grain on starch digestibility, four Angus x Hereford steers (means BW = 350 kg) with duodenal and ileal cannulas were used in a 4 x 4 Latin square design. Diets consisting of 69% ground sorghum grain were fed every 2 h in equal portions (8.2 kg/d). Diets averaged 46.5% starch and 12% CP, except for U, which averaged 14% CP due to urea treatment. Ytterbium attached to sorghum was used as a particulate marker. Duodenal, ileal, and fecal samples were taken 1 h postfeeding after a 14-d adaption to diets. Whole samples were analyzed. Preduodenal starch digestion (%) was 89, 83, 76, and 70, and starch digestion over the total tract was 99, 97, 95 and 91 for R, U, A, and D, respectively. Starch digestion proximal to each site (duodenum and ileum) was enhanced (P less than .05) by R and U compared with D. Within the small intestine, there was a linear relationship (P less than .003) between starch digestion and daily starch supply. However, digestibility of starch in the small intestine (mean = 45%) was not different among diets. Apparent digestibility of starch in the large intestine was not significantly different from digestibility in the small intestine. Urea-treated sorghum grain was equivalent to reconstituted, ensiled sorghum in digestion characteristics and was superior to dry sorghum.