日粮精料进食水平对肉牛消化道营养物质流量和表观消化率的影响

为了研究日粮精料进食水平对肉牛真胃食糜营养流量和营养物质表观消化率的影响,试验选择体重650kg左右荷斯坦(Holstein)公牛3头,安装有瘤胃、真胃瘘管,按3×3拉丁方实验设计分别饲喂粗料进食量相同而精料不同的3种日粮,以三氧化二铬(Cr2O3)作真胃食糜标记物,全收粪法收集粪样,测定真胃食糜和粪中的有机物(OM)、粗蛋白质(CP)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)流量及在瘤胃内、真胃后段消化道(简称肠道)内的表现消化率.结果表明日粮精料进食水平对瘤胃及全消化道的OM、NDF、ADF表观消化率没有显著影响(P＞0.05),日粮精料水平明显影响到达真胃的OM和蛋白质量(P＜0.05),但全消化道CP表观消化率没有差异(P＞0.05).     

日粮蛋白质水平对肉牛真胃营养物质流量和营养物质消化率的影响

本文旨在研究日粮蛋白质水平对肉牛真胃食糜营养流量和营养物质表观消化率的影响。试验选择4头体重(650±20)kg,安装有瘤胃、真胃瘘管的荷斯坦(Holstein)公牛,按4×4拉丁方试验设计分别饲喂精粗比和进食量相同的4种蛋白质水平日粮,以三氧化二铬(Cr2O3)作真胃食糜标记物,全收粪法收集粪样,测定真胃食糜和粪便中的有机物(OM)、粗蛋白质(CP)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)流量及在瘤胃内和真胃后段消化道(简称肠道)内的表观消化率。结果表明:日粮蛋白质水平对瘤胃及全消化道的OM、NDF和ADF表观消化率没有显著影响(P>0.05),日粮蛋白质水平显著影响真胃食糜的粗蛋白质量(P<0.05),但全消化道CP表观消化率没有差异(P>0.05)。     

蛋白质补充料来源对肉牛日粮淀粉瘤胃发酵和小肠消化的影响

为了研究日粮蛋白质补充料来源对肉牛日粮淀粉瘤胃发酵和小肠消化的影响,选择体重600kg左右的荷斯坦(Holstein)公牛3头,安装瘤胃、真胃瘘管,按3×3拉丁方实验设计分别饲喂以豆粕、全脂大豆、过瘤胃蛋白质料为蛋白质补充料来源的3种不同日粮,以三氧化二铬(Cr2O3)作真胃食糜标记物,全收粪法收集粪样,测定真胃食糜和粪中的淀粉流量及在瘤胃内、真胃后段消化道(简称肠道)的表观消化率。结果表明:日粮蛋白质补充料来源对瘤胃及全消化道的淀粉表观消化率没有显著影响(P>0.05),瘤胃和全消化道淀粉的表观消化率分别为78.65%和97.19%。     

不同日粮对肉牛瘤胃可发酵有机物和全消化道有机物表观消化的影响

为了研究不同日粮有机物瘤胃发酵量与全消化道消化量之间的关系,选择体重600 kg左右的荷斯坦(Holstein)公牛3头,安装瘤胃、真胃瘘管,以三氧化二铬(Cr2O3)作真胃食糜标记物,全收粪法收集粪样,测定真胃食糜和粪中的有机物(OM)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)流量及在瘤胃内、全消化道的表观消化,分别以3×3拉丁方和2×3不完全拉丁方试验设计测定不同日粮有机物瘤胃发酵率和消化道表现消化率,试验Ⅰ为饲喂粗料进食量相同而精料进食量不同的3种日粮,试验Ⅱ为以豆粕、全脂大豆为蛋白质补充料来源的2种等蛋白日粮.结果表明:不同日粮对瘤胃及全消化道的OM、NDF、ADF表观消化率没有显著影响(P＞0.05),但明显影响有机物瘤胃可发酵量(P＜0.05);日粮有机物瘤胃表观发酵量(FOM,g/d)与日粮有机物全消化道消化量(DOM,g/d)有显著的相关关系:DOM(g/d)=1.27×FOM(g/d)+962.81(r2=0.95,n=5,P＜0.01).     

绵羊对含不同秸秆的全饲粮颗粒料的消化代谢

选用4只装有十二指肠近端套管的1岁杂种生长羯羊,按2×3交叉设计进行试验,交替饲喂以玉米Zea mays秸和苜蓿Medicago sativa为粗料(A处理)及以小麦Triticum aestivum秸和苜蓿为粗料(B处理)的等消化能(DE)、等氮全饲粮颗粒料;以Cr2O3为食糜标记物并结合全收粪、尿法,测定了绵羊十二指肠食糜流通量,瘤胃内、瘤胃后及全消化道干物质(DM)和氮的表观消化率,全消化道酸性洗涤纤维(ADF)和中性洗涤纤维(NDF)表观消化率及氮表观存留率.结果表明:十二指肠食糜流量、氮流量,瘤胃内、瘤胃后及全消化道DM和氮的消化率在2个处理间差异不显著(P>0.05),全消化道ADF和NDF消化率及氮表观存留率差异也不显著(P>0.05),但A处理全消化道DM和ADF的消化率及氮的表观存留率有大于B处理的趋势.     

饲粮不同粗蛋白质水平对育肥羔羊小肠氨基酸流量及吸收率的影响

本研究旨在比较饲粮不同粗蛋白质(CP)水平对育肥羔羊小肠氨基酸(AA)流量及吸收率的影响。选用体重(30.0±3.7)kg,安装有瘤胃、十二指肠近端和回肠末端瘘管的3只哈萨克羊公羔为试验动物,采用3×3拉丁方试验设计,各处理饲粮CP水平分别为11.00%、12.00%和13.00%;预试期10 d,正试期10 d。采用镱锕(Yb-Ac)、锂铬乙二胺四乙酸(Li Cr-EDTA)分别作为消化道固相和液相食糜标记物测定小肠食糜流量。结果表明:提高饲粮CP水平可增加羔羊氮进食量、表观消化率和氮沉积,13.00%CP处理显著高于11.00%CP处理(P0.05),并有增加饲粮干物质(DM)、有机物(OM)和中性洗涤纤维(NDF)表观消化率的趋势(0.05≤P0.10),但不影响酸性洗涤纤维(ADF)的表观消化率(P0.05)。提高饲粮CP水平虽然对小肠真食糜流量及氨基酸吸收率无显著性影响(P0.05),但十二指肠氮、总氨基酸(TAA)流量以及必需氨基酸(EAA)中精氨酸(Arg)、组氨酸(His)和赖氨酸(Lys)的吸收率在数值上有所增加。结果显示,提高饲粮CP水平有提高消化率、小肠食糜流量及氨基酸吸收率的潜在趋势。     

日粮磷进食水平对西杂后备母牛日粮磷表观消化率的影响

为了研究日粮磷进食量对肉牛日粮磷表观消化的影响,试验选用体况良好、体重一致(347 kg±25 kg)的杂交后备母牛(西门塔尔牛(♂)×中国黄牛(♀))16头,随机分为4组,即处理1、2、3和4组,每组4头,各试验组日粮磷的进食量分别为26、34、42和50 g/d,以精料饲喂量调整磷进食水平(每天育成母牛精料喂量分别为1.5、2.5、3.5和4.5 kg),粗料(玉米秸秆青贮)自由采食。总试验期30 d,预饲期20 d后进入正试期,试验最后7 d全收集粪样。结果表明,不同日粮磷进食量对消化道磷的表观消化量和表观消化率有显著影响(P<0.05),在日粮磷进食量为34g/d(日粮磷水平0.51%)时,消化率达最大(53.8%);日粮磷进食量大于34 g/d时,磷进食的增加使磷的表观消化率明显降低(P<0.05)。     

不同粗蛋白质水平日粮对育肥羊小肠养分吸收率的影响

本研究旨在比较不同粗蛋白质（CP）水平日粮对育肥羔羊小肠养分吸收率的影响。选用体重30 kg左右,安装有瘤胃、十二指肠近端和回肠末端瘘管的3只哈萨克育肥羊为试验动物,采用3×3拉丁方试验设计,采用醋酸镱（Yb-Ac）、锂铬乙二胺四乙酸（LiCr-EDTA）分别作为消化道固相和液相食糜标记物测定小肠食糜流量。结果显示,增加全混合日粮中CP水平可显著提高育肥羊N的进食量、全消化道表观消化率和N沉积（P<0.05）,显著提高干物质（DM）和有机物（OM）的表观消化率（P<0.05）,但对小肠食糜流量无显著影响（P>0.05）;提高日粮CP水平对十二指肠食糜除EE和嘌呤外的营养成分流量均产生显著的影响（P<0.05）,仅对回肠食糜中CP、粗灰分（Ash）、DM、中性洗涤纤维（NDF）和酸性洗涤纤维（ADF）流量的影响显著（P<0.05）,且对CP、Ash、DM、NDF和ADF的小肠吸收率影响显著（P<0.05）。本试验为进一步深入分析增加日粮CP水平对其在育肥羊体内的消化利用奠定基础。     

西门塔尔杂交后备母牛日粮植物源磷进食量对表观可消化磷的影响

旨在采用消化试验研究后备母牛日粮植物源磷进食量与磷表观消化率的关系。试验选用体况良好、体重一致的西杂后备母牛[西门塔尔牛(♂)×中国黄牛(♀)]24头,随机分为6组,即试验1组、2组、3组、4组、5组和6组,每组4头,分别定量(3.50kg/d)饲喂6种不同磷水平的精料日粮,粗料(青贮)自由采食。使用麸皮调节日粮精料磷水平,各试验组精料磷水平分别为0.36%、0.40%、0.42%、0.46%、0.50%和0.54%;总试验期为30d,预饲期20d后进入正试期,试验最后7d全收集粪样和尿样。饲料样及粪样均测定其中磷和干物质含量,计算粪磷排泄量与日粮磷进食量的回归关系。结果表明,不同日粮处理间消化道磷的表观消化量和表观消化率有显著差异(P<0.05),并随进食磷量的增加而增加,但消化道表观消化的磷量与磷的进食不是直线关系,而是呈现抛物线关系,在日粮磷水平为0.42%时,消化量和消化率达最大,即分别为10.5g/d和40.8%。     

日粮精料中麸皮比例对西门塔尔杂交后备母牛日粮营养物质消化率的影响

文章旨在采用消化试验研究肉牛日粮精料中麸皮比例对日粮营养物质表观消化率的影响。试验选取体况良好、体重一致(369.5 kg±37.8 kg)的杂交后备母牛(西门塔尔牛(♂)×中国黄牛(♀))24头,随机分为6组,即试验Ⅰ组、Ⅱ组、Ⅲ组、Ⅳ组、Ⅴ组和Ⅵ组,每组4头,分别定量饲喂6种不同麸皮水平的精料日粮(3.5kg/d),粗料(青贮)自由采食;各试验组精料麸皮水平分别为0%、10%、20%、30%、40%和50%;预饲期20 d,试验期30 d,试验最后7 d收集全部粪样。结果表明:日粮精料中麸皮水平对日粮有机物(OM)、粗蛋白质、淀粉和中性洗涤纤维(NDF)的消化道表观消化率没有显著影响(P>0.05),不同麸皮水平日粮的OM、CP、淀粉和NDF的消化道表观消化率变化范围分别为49.40%～55.52%、48.56%～53.90%、88.87%～93.29%、48.11%～57.91%。     

Influence of mass of ruminal contents on voluntary intake and digesta passage in steers fed a forage and a concentrate diet

To evaluate the influence of mass of ruminal contents on voluntary intake and ruminal function, five ruminally cannulated steers (550 kg) were fed an orchard grass hay diet ad libitum in a 5 x 5 Latin square experiment. The mass of ruminal contents was altered by adding varying weights of modified tennis balls to the rumen before the initiation of each 15-d experimental period. Treatments consisted of 50 balls with a specific gravity of 1.0, 1.1, 1.2, 1.3, or 1.4; the total weight of the balls was 7.45, 8.50, 9.25, 10.55, and 11.55 kg, respectively. Increasing the specific gravity of the balls added to the rumen decreased DMI and particle passage rate (P < 0.05) in a linear manner. A second experiment was conducted to evaluate the influence of mass of ruminal contents on voluntary intake and ruminal function of both forage and concentrate diets. Five ruminally cannulated steers (580 kg) were fed a 70% concentrate (DM basis) or an orchardgrass hay diet ad libitum in a 5 x 5 Latin square experiment. The mass of ruminal contents was altered as in the first experiment. Treatments consisted of 0 balls added to the rumen of steers fed concentrate diet (control), 75 balls with a specific gravity of 1.1 given to steers fed a concentrate diet, 75 balls with a specific gravity of 1.4 given to steers fed a concentrate diet, 75 balls with a specific gravity of 1.1 given to steers fed a hay diet, and 75 balls with a specific gravity of 1.4 given to steers fed hay diet. The addition of balls to the rumen of steers fed the concentrate diet decreased DMI (P < 0.05) compared with the 0-ball treatment, and increasing specific gravity of balls also decreased DMI (P < 0.01) for both concentrate and hay diets. Adding balls to the rumen of steers fed the concentrate diet decreased particle passage rate (P < 0.05), whereas increasing specific gravity of balls decreased particle passage rate for both concentrate and hay diet. The results of this study suggest that the density of ruminal digesta can have an influence on voluntary intake of both forage and concentrate diets.     

Influence of dietary urea level on digestive function and growth performance of cattle fed steam-flaked barley-based finishing diets

Four Holstein steers (282 kg) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square experiment to evaluate the influence of dietary urea level (0, 0.4, 0.8, and 1.2%, DM basis) in a steam-flaked barley-based finishing diet on digestive function. There were no treatment effects (P > 0.20) on ruminal digestion of OM and ADF. Increasing dietary urea level increased (linear, P < 0.01) ruminal starch digestion. Ruminal degradability of protein in the basal diet (no supplemental urea) was 60%. Increasing dietary urea level did not increase (P > 0.20) ruminal microbial protein synthesis or nonammonia N flow to the small intestine. There were no treatment effects (P > 0.20) on total-tract ADF digestion. Total tract digestion of OM (quadratic, P < 0.01) and starch (linear, P < 0.05) increased slightly with increasing urea level. Urea supplementation increased (linear, P < 0.01) ruminal pH 1 h after feeding; however, by 3 h after feeding, ruminal pH was lower (cubic, P < 0.05) with urea-supplemented diets. Urea supplementation did not affect (P > 0.20) ruminal molar proportions of acetate and propionate. One hundred twenty crossbred steers (252 kg; approximately 25% Brahman breeding) were used in an 84-d feeding trial (five pens per treatment) to evaluate treatment effects on growth performance. Daily weight gain increased (linear, P = 0.01) with increasing urea level, tending to be maximal (1.53 kg/d; quadratic, P = 0.13) at the 0.8% level of urea supplementation. Improvements in ADG were due to treatment effects (linear, P < 0.01) on DMI. Urea supplementation did not affect (P > 0.20) the NE value of the diet for maintenance and gain. Observed dietary NE values, based on growth performance, were in close agreement with expected based on tabular values for individual feed ingredients, averaging 100.4%. We conclude that with steam-flaked barely-based finishing diets, ruminal and total-tract digestion of OM and ruminal microbial protein synthesis may not be increased by urea supplementation. In contrast, ADG was optimized by dietary inclusion of 0.8% urea. Urea supplementation may not enhance the net energy value of steam-flaked barely-based finishing diets when degradable intake protein is greater than 85% of microbial protein synthesis.     

Rumen fermentation and starch degradation by Holstein steers fed sodium-hydroxide- or formaldehyde-treated wheat

The authors investigated the effect of feeding 2% sodium-hydroxide-treated (as-fed basis) or 2% formaldehyde-treated (crude protein basis) wheat to rumen-, duodenal- and ileocaecal-cannulated Holstein steers on rumen fermentation and ruminal and postruminal starch degradation. Feeding 2 kg/day wheat treated with sodium hydroxide (NaOH) or formaldehyde did not affect negatively the main parameters of rumen fermentation, i.e. pH, short-chain fatty acid (SCFA) production, and microbial activity. Fibre degradation in the rumen was significantly improved when NaOH-treated wheat was fed. The in vivo experiments demonstrated that feeding NaOH- and formaldehyde-treated wheat to steers significantly increased the amount of starch that reached the small intestine. The amount of starch that entered the duodenum increased by 57% and 75% when steers were fed NaOH- and formaldehyde-treated wheat compared to the control phase, respectively. This higher quantity of starch was digested and absorbed, which can provide an increased glucose supply to the animals.     

Supplemental cracked corn for steers fed fresh alfalfa: I. Effects on digestion of organic matter, fiber, and starch

The effect of supplementation with different levels of cracked corn on the sites of OM, total dietary fiber (TDF), ADF, and starch digestion in steers fed fresh alfalfa indoors was determined. Six Angus steers (338 +/- 19 kg) fitted with cannulas in the rumen, duodenum, and ileum consumed 1) alfalfa (20.4% CP, 41.6% NDF) ad libitum (AALF); 2), 3), and 4) AALF supplemented (S) with .4, .8, or 1.2%, respectively, of BW of corn; or 5) alfalfa restricted at the average level of forage intake of S steers (RALF), in a 5 x 5 Latin square design. Total OM intake was lower (P < .01) in steers fed RALF than in those fed AALF but level of forage intake did not affect sites of OM, TDF, or starch digestion (P > .05). Forage OM intake decreased (P < .01) linearly (8,496 to 5,840 g/d) but total OM intake increased (P = .03) linearly (8,496 to 9,344 g/d) as corn increased from .4 to 1.2% BW. Ruminal apparent and true OM disappearance was not affected, but OM disappearing in the small intestine increased (P < .01) linearly with increasing levels of corn. Total tract OM digestibility (71.2 to 76.2%) and the proportion of OM intake that was digested in the small intestine (15.4 to 24.5%) increased (P < .01) linearly as corn increased. The TDF and ADF intakes decreased (P < .01) linearly as level of corn increased. Total tract TDF and ADF digestibilities were not different among treatments (average 62.9 and 57.8%, respectively). Starch intake and starch digested in the rumen and small and large intestine increased (P < .01) linearly with increasing corn level. Ruminal pH and VFA concentrations decreased and increased (P < .01), respectively, with increasing corn. Supplementation with corn increased OM intake, decreased forage OM intake, and increased the proportion of OM that was digested in the small intestine, but fiber digestion was not affected.     

Intestinal starch disappearance increased in steers abomasally infused with starch and protein

Steers (379 +/- 10 kg) with ruminal, duodenal, and ileal cannulas were used in a 5 x 5 Latin square digestion trial to quantify and evaluate the relationship between intestinal protein supply and intestinal starch disappearance. Treatments were infusions of 0, 50, 100, 150, or 200 g/d of casein along with 1,042 g/d of raw cornstarch. Abomasal infusions were accomplished by passing tubing and a pliable retaining washer through the reticular-omasal orifice into the abomasum. Steers were fed a 93% corn silage, 7% supplement diet that contained 12% crude protein at 1.65% body weight in 12 equal portions/d. Periods lasted 17 d (12 d for adaptation, 2 d of collections, and 3 d of rest). The quantity and percentage of organic matter and protein disappearance from the small intestine increased linearly (P < 0.03) with infused casein. Greater quantities of starch disappeared with increased casein infusion (P < 0.01). The infusion of 200 g/d of casein increased small intestinal starch disappearance by 226 g/d over the control. Casein infusion did not affect the quantity or percent of organic matter, starch, or protein disappearance in the large intestine. Treatments did not change ruminal ammonia N, ruminal pH, or plasma glucose concentrations. Starch disappearance from the small intestine was increased with greater protein flow to the duodenum of steers.     

The effects of dry extrusion temperature of whole soybeans on digestion of protein and amino acids by steers

Five Holstein steers (450 kg) with cannulas in the rumen, proximal duodenum, and terminal ileum were used in a 5 x 5 Latin square design to study the effects of extrusion temperature on site of digestion of nitrogenous compounds in whole soybeans. The basal diet contained 50% corn silage, 24% alfalfa hay, 16.6% corn starch, 4.05% ground corn, 1% urea, and 3.4% soybean oil. Raw soybeans or soybeans extruded at 116, 138, or 160 degrees C (diets 116, 138, and 160, respectively) replaced the soybean oil and most of the corn starch in the test diets. Total N (g/d) reaching the duodenum was 232, 293, 285, 308, and 299 for the basal, raw, 116, 138, and 160 diets, respectively. No differences were observed between the raw and extruded soybeans (P = 0.81), or for the linear or quadratic effects of extrusion temperature (P = 0.56 and P = 0.45, respectively). Nonbacterial N (g/d) reaching the duodenum was 63.1, 104.6, 106.7, 101.9, and 113.9 for the same diets, respectively, and was not influenced by extrusion or extrusion temperature. Nitrogen disappearance from the small intestine (g/d) was 150 for the basal diet, 194 for the raw soybean diet, and 187,221, and 213 for the 116,138, and 160 degrees C extruded diets, respectively; no differences were observed between the raw and the extruded soybeans, or for diets containing soybeans extruded at different temperatures. Nitrogen disappearance (% of N entering) from the small intestine was lower (P < 0.05) for steers fed the basal diet than for steers fed the soybean-supplemented diets (64.1 vs 68.5%). No differences (P > 0.10) due to extrusion temperature were detected for flows of individual, essential AA, nonessential AA, and total AA at the duodenum. As extrusion temperatures increased, there were linear increases (P < 0.10) in disappearance (g/d) of all individual AA from the small intestine except for methionine and glycine. Essential, nonessential, and total AA disappearance from the small intestine were increased linearly (P < 0.10) with increasing extrusion temperature. Extrusion of soybeans can protect soy protein against extensive ruminal degradation without compromising intestinal digestibility.     

Influence of ruminal and postruminal carbohydrate infusion on visceral organ mass and adipose tissue accretion in growing beef steers

Forty crossbred beef steers (243 +/- 2 kg of BW) with ruminal and abomasal infusion catheters were used to test 2 hypotheses: 1) visceral mass is responsive to energy input and site of carbohydrate (CHO) infusion and 2) rate and site of adipose accretion are dependent on site of CHO infusion and complexity. Treatments included a pelleted, forage-based, basal diet fed at 161 (LI) or 214 (HI) kcal of ME/(kg of BW(0.75) x d), LI plus ruminal (R-SH) or abomasal (A-SH) infusion of a partial starch hydrolysate (SH), and LI plus abomasal infusion of glucose (A-G). The basal diet was fed in 12 equal portions daily at 2-h intervals, with starch and glucose infused over a 22-h period at rates of 12.6 and 14.4 g/(kg of BW(0.75) x d). After 35 d of infusion, steers were slaughtered; and visceral organ and adipose mass, subcutaneous adipose thickness over the 5th and 12th rib, and LM intramuscular fat concentration were determined. Total intake energy (IE) increased (P = 0.0001) with ME intake. Dietary IE was similar between LI and CHO treatments, but total IE increased (P < 0.001) with CHO infusion. Greater dietary ME intake and CHO infusion increased or tended (P < or = 0.09) to increase final BW and HCW. As a percentage of empty BW, total stomach complex, rumen, omasum, liver, pancreas, and kidney weights were greater (P < or = 0.05) for HI vs. LI. Stomach complex, rumen, pancreas, and kidney weights as a percentage of empty BW were greater (P < or = 0.05) for R-SH vs. A-SH. Compared with ASH, A-G increased (P < or = 0.02) total and mucosal weights from the 10-cm sections of the ileum. Increases in rumen mass were associated with no change or an increase in rumen total and mucosal DNA concentrations. Greater dietary ME tended (P = 0.06) to increase subcutaneous fat thickness at the 5th rib but did not affect alimentary adipose accretion on an empty BW basis. Omental and total alimentary adipose weights were increased (P < or = 0.04) by A-G compared with A-SH. Although SH infusion did not alter adiposity, there was a consistent numerical pattern in total alimentary and subcutaneous fat depots with CHO infusion (A-G > ASH > R-SH). Our findings demonstrate that increasing ruminal CHO supply results in a disproportionate increase in rumen mass, whereas increasing small intestinal CHO supply does not alter gastrointestinal organ mass. Small intestinal energy in the form of glucose resulted in greater adipose accretion, particularly the omental depot.     

Influence of forage level on response of feedlot steers to salinomycin supplementation

Two trials were conducted to evaluate the influence of forage level on the response of feedlot cattle to salinomycin. Diets containing 10, 15 and 20% forage were compared with 0 or 11 mg/kg salinomycin. In trial 1, treatment effects on feedlot performance were evaluated using 108 crossbred steers (295 kg) in a crossover design experiment. There were no salinomycin X forage level interactions (P greater than .20). Weight gain response to salinomycin supplementation averaged 5.4, 5.3 and 6.9%, respectively, for diets containing 10, 15 and 20% forage. Corresponding values for feed conversion response to salinomycin supplementation were 5.1, 3.9 and 5.9%. Averaged across forage level, salinomycin supplementation improved rate of weight gain and feed conversion by 5.9 and 5.2%, respectively (P less than .01). In trial 2, treatment effects on characteristics of ruminal and total tract digestion were evaluated in a 6 X 6 Latin-square design trial involving six crossbred steers (191 kg) with cannulae in the rumen and proximal duodenum. There were no interactions between salinomycin supplementation and forage level on characteristics of ruminal digestion (P greater than .20). Salinomycin supplementation did not influence synthesis of microbial N, ruminal digestion of organic matter, acid detergent fiber and starch, or molar proportions of acetate, propionate and butyrate (P greater than .20). Salinomycin supplementation increased passage of non-ammonia N to the small intestine (5.4%, P less than .10) and increased ruminal escape of feed N (24%, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.