Compartmental modeling with nitrogen-15 to determine effects of degree of fat saturation on intraruminal N recycling

Two- and three-compartment models were developed to describe N kinetics within the rumen using three Holstein heifers and one nonlactating Holstein cow fitted with ruminal and duodenal cannulas. A 4 x 4 Latin square design included a control diet containing no supplemental fat and diets containing 4.85% of diet dry matter as partially hydrogenated tallow (iodine value = 13), tallow (iodine value = 51), or animal-vegetable fat (iodine value = 110). Effects of fat on intraruminal N recycling and relationships between intraruminal N recycling and ruminal protozoa concentration or the efficiency of microbial protein synthesis were determined. A pulse dose of 15(NH4)2SO4 was introduced into the ruminal NH3 N pool, and samples were taken over time from the ruminal NH3 N and nonammonia N pools. For the three-compartment model, precipitates of nonammonia N after trichloroacetic acid and ethanol extraction were defined as slowly turning over nonammonia N; rapidly turning over nonammonia N was determined by difference. Curves of 15N enrichment were fit to models with two (NH3 N and nonammonia N) or three (NH3 N, rapidly turning over nonammonia N, and slowly turning over nonammonia N) compartments using the software SAAM II. Because the three-compartment model did not remove a small systematic bias or improve the fit of the data, the two-compartment model was used to provide measurements of intraruminal N recycling. Intraruminal NH3 N recycling (45% for control) decreased linearly as fat unsaturation increased (50.2, 43.0, and 41.7% for partially hydrogenated tallow, tallow, and animal-vegetable fat, respectively). Intraruminal nitrogen recycling was not correlated with efficiency of microbial protein synthesis or ruminal protozoa counts.     

Effects of chemical hydrogenation of supplemental fat on relative apparent lipid digestibility in finishing swine

Four experiments were conducted to evaluate lipid digestibility in finishing swine fed chemically hydrogenated fats. Dietary chromic oxide was used as an inert marker to measure the apparent digestibility of supplemental fat (SF) that consisted of fully hydrogenated (FH), partially hydrogenated (PH), or PH products blended with other fat sources. In Exp. 1, diets containing 5% SF (as-fed basis) comprising 100, 66.7, 33.3, or 0% FH animal fat (iodine value = 2.5), with the balance contributed by soy oil, were fed to gilts (n = 24). Apparent digestibility increased linearly (-12.0, 26.0, 61.2, and 72.6%; P < 0.001) as the amount of FH fat in the diet decreased, suggesting the digestibility of FH to be near zero. Experiment 2 (2 x 4 factorial; n = 48) evaluated diets containing 5% (as-fed basis) blended fat (FH tallow and yellow grease) to achieve iodine values of 20, 30, 40, or 50 compared with PH tallow with identical iodine values. Digestibility of diets formulated with PH tallow was greater than those containing blended fat (73.4 vs. 67.2%; P < 0.01), especially at lower iodine values (interaction; P < 0.10). In Exp. 3, digestibility was measured in pigs (n = 96) fed 5% (as-fed basis) PH choice white grease with iodine values of 20, 40, 60, or 80. Increasing iodine value did not alter digestibility (66.2, 69.2, 68.2, and 69.7%). Experiment 4 investigated digestibility (n = 32) of diets formulated with 8% (as-fed basis) PH fat (iodine value 20 or 50) with 0.10% lysolecithin as an emulsifier. Lipid digestibility was 14.5% greater in the 8% SF diet with an iodine value of 50 compared with the diet with an iodine value of 20 (79.15 vs. 69.12%; P < 0.001), but lysolecithin was without effect. These experiments indicate that partial hydrogenation is superior to blending unsaturated fat with saturated fat sources and that digestibility is not greatly affected by decreasing the iodine value via partial hydrogenation.     

The effect of dietary ratios of corn silage and alfalfa hay on carbohydrate digestion and retention time of feed particles in the gastrointestinal tract of steers

Four Holstein steers fitted with duodenal cannula were used in a 4 × 4 Latin square design to investigate the effect of the combination of corn silage (CS) and alfalfa hay (AH) in different ratios on the ruminal and intestinal digestion of carbohydrates and feed particle passage rate. Steers were fed mixed diets containing both CS and AH in ratios of 80:20, 60:40, 40:60 and 20:80 on a dry matter basis at 95% of ad libitum feed intake. The increase of AH proportion in diets increased dry matter intake and ruminal digestion of dry matter, non-fiber carbohydrate, neutral and acid detergent fiber linearly. Ruminal digestibility of neutral detergent fiber showed a quadratic response, and total digestibility increased linearly with increasing AH proportion. Digestibility of acid detergent fiber in the rumen was not affected by the dietary treatments, but the total tract digestibility increased as the AH proportion increased. Mean retention time of feed particles in total compartment increased when the AH proportion increased from 20% to 60%, but decreased with further increase of the AH proportion. These results indicate that moderate combinations of CS and AH have an associative effect on ruminal fiber digestion, modifying particle movement in the rumen.     

Effect of fats and fatty acid combinations on ruminal fermentation in semi-continuous in vitro cultures

Four in vitro trials were conducted to determine how ruminal fermentation is affected by source of fat, level of fat, and combinations of fatty acids. Trials I and II examined how volatile fatty acids (VFA) were changed by three sources of fat (blended animal-vegetable fat, corn oil and tallow fatty acids) each added to a hay substrate at six levels (0, 2, 4, 6, 8 and 10%). Increasing blended fat caused no changes in VFA levels except to decrease butyric acid from 12.1 to 9.9% of the total VFA (P less than .05). Corn oil and tallow fatty acids both increased propionic acid, causing the ratio of acetic to propionic acids (A/P) to decrease (P less than .01). Trial III tested different ratios of oleic/stearic and linoleic/stearic acids to determine if certain combinations were better for fermentation. There was no evidence of synergism among fatty acids since increasing the ratio of unsaturates steadily reduced A/P. Trial IV was designed to determine how changes in VFA levels reflect changes in fiber digestibility of substrates containing added fat. Volatile fatty acids having significant regressions with fiber digestibility were acetic acid (r = .648), propionic acid (r = -.670), total VFA concentration (r = .742) and A/P (r = .831). Results are interpreted to show that blended animal-vegetable fats are less toxic in the rumen than equal levels of other lipids, and the beneficial effects of blended fat cannot be attributed to a unique combination of fatty acids acting synergistically.     

Low-quality roughages in high-concentrate pelleted diets for sheep: digestion and metabolism of nitrogen and energy as affected by dietary fiber concentration

Two trials were conducted to evaluate effects of, and interactions between, level and source of fiber in the diet on ruminal environment, microbial protein synthesis, nutrient digestion and flow of digesta through the gastrointestinal tract of multiple-fistulated sheep (trial 1; 4 X 4 Latin square design) and on ruminal, digestive and metabolic characteristics of early-weaned lambs (trial 2; randomized complete block design; 3 periods). All diets tested were pelleted and were formulated to contain either 39% or 25% neutral detergent fiber (NDF), with corncobs or cottonseed hulls (CSH) as the major NDF (roughage) sources. In trial 1, dry-matter (DM) and organic-matter (OM) digestibilities were not different (P greater than .05) among treatments. Digestibility of NDF was higher (P less than .05) with high-fiber. Bacterial N synthesis (g N/kg OM truly digested) was not different (P greater than .05) among treatments. Molar proportion acetate was higher (P less than .05) and molar proportion propionate lower (P less than .05) when sheep were fed high-fiber diets. In trial 2, apparent DM digestibility was higher (P less than .05) for lambs fed diets containing corncobs. Energy digestibility was higher (P less than .05) at the low-fiber level and for lambs fed diets containing corncobs. Apparent NDF digestibility by lambs was higher (P less than .05) at the high-fiber level and for lambs fed diets containing corncobs. Nitrogen retained (percentage of N intake) was higher (P less than .05) for lambs fed diets containing CSH. Ruminal pH and molar proportion acetate were higher (P less than .05) and molar proportion propionate lower (P less than .05) for lambs fed high-fiber diets. Although responses to corncob vs CSH inclusion in high-energy pelleted diets differ, both roughages are effective as fiber sources in sheep diets.     

Dynamics of methanogenesis,ruminal fermentation and fiber digestibility in ruminants following elimination of protozoa: a meta-analysis

Background: Ruminal microbes are vital to the conversion of lignocellulose-rich plant materials into nutrients for ruminants.Although protozoa play a key role in linking ruminal microbial networks,the contribution of protozoa to rumen fermentation remains controversial; therefore,this meta-analysis was conducted to quantitatively summarize the temporal dynamics of methanogenesis,ruminal volatile fatty acid(VFA) profiles and dietary fiber digestibility in ruminants following the elimination of protozoa(also termed defaunation).A total of 49 studies from 22 publications were evaluated.Results: The results revealed that defaunation reduced methane production and shifted ruminal VFA profiles to consist of more propionate and less acetate and butyrate,but with a reduced total VFA concentration and decreased dietary fiber digestibility.However,these effects were diminished linearly,at different rates,with time during the first few weeks after defaunation,and eventually reached relative stability.The acetate to propionate ratio and methane production were increased at 7 and 11 wk after defaunation,respectively.Conclusions: Elimination of protozoa initially shifted the rumen fermentation toward the production of more propionate and less methane,but eventually toward the production of less propionate and more methane over time.     

Low-quality roughages in high-concentrate pelleted diets for sheep: digestion and metabolism characteristics as affected by corncob and(or) rice hull additions

Two trials were conducted to determine effects of feeding corncobs, rice hulls or a combination of both on nutrient digestion and flow of digesta through the gastrointestinal tract of multiple-cannulated sheep (55-kg Rambouillet X Dorset rams; trial 1; 4 X 4 Latin square) as well as ruminal, digestive and metabolic characteristics of early-weaned lambs (24.1-kg crossbred rams; trial 2; randomized complete block design; 3 periods) fed pelleted 75% concentrate-25% roughage diets. In trial 1, apparent total tract dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF) digestibilities decreased and N digestibility increased as percentage of dietary corncobs decreased and percentage of rice hulls increased. Site of NDF digestion appeared to shift from the upper to the lower digestive tract as percentage of corncobs decreased and percentage of rice hulls increased. In trial 2, apparent DM digestibility decreased as corncobs were replaced with rice hulls in the diet. Neutral detergent fiber digestibility was not affected by diet except in larger lambs at higher intakes, with NDF digestibility generally decreasing as percentage of dietary rice hulls increased. Nitrogen digestibility was not affected by replacing corncobs with rice hulls in the diet. Ruminal pH decreased as rice hulls replaced corncobs in the diet. These data are interpreted to indicate that rice hulls can be effectively substituted for corncobs in sheep diets when added at levels up to 25% of the total diet.     

Effects of saturation and esterification of fat sources on site and extent of digestion in steers: digestion of fatty acids, triglycerides, and energy.

Five steers (mean BW 526 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a 5 x 6 Youden square design with 14-d periods. Diets contained chopped alfalfa hay, corn silage, and concentrate (25:35:40, DM basis). Treatments were 1) control (no added fat); 2) tallow (T), iodine value (IV) = 51.5; 3) partially hydrogenated tallow (PHT), IV = 30.7; 4) hydrogenated tallow (HT), IV = 6.9; 5) blend (1: 1) of HT and hydrogenated free fatty acids (HTHFA), IV = 9.0; and 6) hydrogenated free fatty acids (HFA), IV = 11.2. Fats replaced cornstarch in the control diet to supply 5% added fatty acids. Intake was restricted to 90% of ad libitum; DMI was similar among diets (mean 9 kg/d). Total fatty acid intake averaged 170, 500, 506, 525, 489, and 491 g/d for treatments 1 to 6, respectively. Flows of total C16, total C18, and total fatty acids to the duodenum were increased by supplemental fat; flows of total C18 and total fatty acids were greater than their intake for all treatments. Flow of total fatty acids associated with ruminal bacteria accounted for 50 and 17% of the total duodenal fatty acid flow for the control and fat-supplemented diets, respectively. Digestibility of total fatty acids entering the small intestine (74, 71, 62, 39, 53, and 63% for treatments 1 to 6, respectively) was greater for the control diet than for fat-supplemented diets and decreased as either saturation (T < PHT < HT) or esterification (HFA < HTHFA < HT) increased. Digestibilities of fatty acids in the total tract followed similar patterns. Ruminal lipolysis of dietary triglycerides decreased linearly as the degree of saturation of fat sources increased. Small intestinal disappearance of triglycerides (89, 75, 51, 44, 64, and 73% of duodenal flow for treatments 1 to 6, respectively) decreased linearly as either saturation or esterification increased. Flows and digestion of gross energy followed patterns similar to those for fatty acids and triglycerides. Resistance to ruminal and small intestinal lipolysis is a major factor contributing to the poor digestibility of highly saturated triglycerides.     

Effect of roughage particle size on ruminal, digestive and metabolic characteristics of early-weaned lambs fed pelleted corncob-concentrate diets

Two experiments were conducted to determine effects of feeding corncobs of various mean particle size (MPS) on ruminal, digestive and metabolic characteristics of early-weaned lambs fed pelleted 74.9% concentrate:25.1% corncob diets. The MPS of corncobs in diets was 6.5, 5.4, 1.4 and .8 mm, respectively. As particle size decreased, percentage starch decreased and percentage neutral detergent fiber (NDF), acid detergent fiber (ADF) and cellulose increased. In Exp. 1, 28 crossbred rams (seven/treatment, avg initial wt, 15.3 kg) were used in a randomized complete-block design. In Exp. 2, lambs from Exp. 1 were re-weighed (avg initial wt, 16.8 kg) and fed the same diets as in Exp. 1. In Exp. 1 and 2, lambs ingested dry matter (DM) equal to 2.68 and 3.74% of body weight, respectively. In Exp. 1, apparent DM digestibility was unaffected by corncob MPS; however, in Exp. 2, DM digestibility was highest (68.8%) for lambs fed the 6.5-mm diet and lowest (63.8%) for those fed the .8-mm diet. Apparent starch digestibility was high (greater than 98.8%) in both experiments. Neutral detergent fiber and ADF digestibilities were highest for lambs fed the 1.4-mm diet (50.5 and 43.6%, Exp. 1; 39.6 and 28.9%, Exp. 2). A dramatic increase (6.8 to 39.1%) in acid detergent lignin (ADL) digestibility was observed in Exp. 1 as corncob MPS decreased. In Exp. 2, ADL digestibilities were similar for lambs fed the 6.5-, 5.4- or 1.4-mm diets (avg value, 5.9%) and highest for those fed the .8-mm diet (29.7%). Nitrogen metabolism was unaffected by corncob MPS. In Exp. 1, digestible energy intake, corrected for urinary losses, did not differ among treatments but in Exp. 2, lambs consuming the 6.5-mm diet had higher corrected digestibility energy intakes (1,926.6 kcal/d) than did those fed other diets (avg, 1,832.4 kcal/d). Ruminal pH sampled 4 h post-feeding was highest for lambs consuming the 6.5-mm diet (6.25) in Exp. 1 and the 1.4-mm diet (5.89) in Exp. 2. Lowest ruminal pH (5.30 and 5.36, respectively) was for lambs consuming the .8-mm diet in Exp. 1 and the 5.4-mm diet in Exp. 2. Ruminal lactate concentrations were variable within and among treatments. Total ruminal volatile fatty acid (VFA) concentrations were similar across treatments but in Exp. 2, there was a shift in molar proportions from acetate to propionate as corncob MPS decreased.(ABSTRACT TRUNCATED AT 400 WORDS)     

不同纤维水平日粮对内蒙古白绒山羊瘤胃发酵的影响

选用2.5岁体重相近,安装永久性瘤胃瘘管的内蒙古白绒山羊羯羊18只,采用完全随机试验设计,分成6组,每组3只。分别饲喂中性洗涤纤维(NDF)水平为49%、52%、55%、59%、62%和65%日粮,预试期14d,正试期4d,正试期内每天06:00、10:00、13:00和18:00采集瘤胃液,测定pH、氨态氮浓度、瘤胃微生物蛋白(MCP)和挥发性脂肪酸(VFA)含量。结果表明:各处理组绒山羊瘤胃pH在10:00和13:00时显著下降(P<0.05),日粮不同NDF水平对瘤胃pH有影响;各处理组绒山羊瘤胃氨氮浓度在10:00时达到最高值,日粮NDF水平为52%和55%时适于微生物蛋白合成所需氨氮浓度;不同时间点间各处理组绒山羊瘤胃MCP浓度差异不显著(P>0.05),日粮NDF水平为52%和55%时MCP浓度最高;各处理组绒山羊瘤胃中乙酸、丙酸和丁酸浓度18:00都达到最低值,不同时间点各处理组VFA浓度无较大变化。本试验表明,内蒙古白绒山羊日粮NDF水平为52%和55%时有最适宜的瘤胃发酵水平。     

Fatty Acid Metabolism in the Digestive Tract of Lactating Cows Fed Tallow in Increasing Amounts at Two Feed Levels

Abstract

Long-chain fatty acid metabolism in the digestive tract was studied in lactating cows fed at two levels of dry matter intake (L, 8.6 kg DM and H, 12.6 kg DM), with 0, 4 and 6% added tallow at low feed level (L0, L4 and L6), and 0, 2, 4 and 6% fat at high feed level (H0, H2, H4 and H6). Mean fatty acid balance from mouth to duodenum was about zero when corrected for endogenous fatty acids from bile. However, regression analysis showed a microbial synthesis of 68 g at zero fatty acid intake, and a trend which indicated declining de novo synthesis of fatty acids with increasing fat level in the diet. As a mean 68% of the unsaturated C18 fatty acids were hydrogenated in the rumen.

Fatty acid and crude fat true digestibilities decreased with increasing fat intakes owing to a decrease in stearic acid (C18:0) digestibility.     

Effects of lecithin and corn oil on site of digestion, ruminal fermentation and microbial protein synthesis in sheep

Six Hampshire wethers with ruminal and duodenal cannulas were fed three diets in a replicated 3 X 3 latin square to compare phospholipids with triglycerides for their effects on ruminal digestion. The diets (56% concentrate, 44% bermuda-grass hay, air-dried basis) contained either no added fat (control), 5.2% soybean lecithin or 2.4% corn oil on a DM basis. All diets were isonitrogenous and both fat-supplemented diets had similar fatty acid and energy contents. Fat added to the diet, regardless of source, reduced digestibilities of DM, energy, ADF and fatty acids in the rumen but had no effect on total tract digestibility coefficients. Lecithin slightly increased (P = .06) fatty acid digestion in the hindgut compared to corn oil (91.0 and 87.0%, respectively). Both fat sources decreased (P less than .01) ruminal ammonia concentration and increased (P less than .10) N flow to the duodenum. Added fat also reduced ruminal (P less than .01) and total tract (P less than .05) N digestibilities. Microbial N flow to the hindgut was not affected by diet, but adding fat increased (P less than .06) true efficiency of microbial protein synthesis. Overall, phospholipids from soybean lecithin inhibited ruminal fermentation similarly to triglycerides from corn oil. Despite ruminal degradation of lecithin by microbial phospholipases as shown in other studies, feeding lecithin tended to increase fatty acid digestion in the hindgut.     

Monensin effects on digestibility, ruminal protein escape and microbial protein synthesis on high-fiber diets

The influence of monensin level (0, 6.1, 12.2, 18.3 and 36.6 ppm) on diet fiber digestibility, microbial protein synthesis and ruminal escape of dietary protein was evaluated in two steer metabolism trials. A growth trial was conducted to study possible interactions of forage quality and monensin level. In metabolism trial 1, four ruminal-cannulated steers were assigned to four monensin levels in a 4 X 4 Latin square design to measure fiber digestibility, rate of passage and protein metabolism. In metabolism trial 2, five duodenal-cannulated steers were assigned to five monensin levels in a 5 X 5 Latin square design to measure fiber digestibility, bacterial N flow and plant N flow. In the two metabolism trials, the level of monensin influenced organic matter (OM) digestibility, neutral detergent fiber (NDF) digestibility and ruminal NDF digestibility quadratically, with the intermediate levels of monensin being superior either to the high level of monensin or no monensin. A quadratic increase in particulate disappearance rate (P = .09) and no effect (P = .95) on liquid disappearance were also observed in trial 1. In trial 1, monensin level quadratically decreased (P = .10) the bacterial protein concentration and increased (P = .02) the ratio of total N:diaminopimilic acid in whole rumen contents. In trial 2, no overall difference in duodenal N flow (P = .64) or flow of individual amino acids (P = .46) was observed. In the growth trial, no interaction of cornstalk quality and monensin was observed (P less than .38).(ABSTRACT TRUNCATED AT 250 WORDS)     

The Influence of Tallow on Rumen Metabolism,Microbial Biomass Synthesis and Fatty Acid Composition of Bacteria and Protozoa

Abstract

Rumen metabolism, microbial biomass synthesis and microbial long chain fatty acid composition were studied in lactating cows fed at two levels of dry matter intake (L, 8.6 kg DM and H, 12.6 kg DM) with 0, 4 and 6% added tallow at the low feed level (L0, L4 and L6) and 0, 2, 4 and 6% at the high feed level (H0, H2, H4 and H6).

Fibre digestibility was not significantly affected by tallow addition. Increasing tallow level in the diet decreased the total VFA concentration, the ratio of acetic acid to propionic acid and the ammonia concentration in the rumen. Crude fat and fatty acid content in bacterial and protozoal dry matter increased with increased tallow level, especially due to an increase in fatty acids originating from the feeds. Microbial synthesis in the rumen and flow of amino acids to the duodenum was highest for medium fat intake at the high feed level.     

Influence of level and source of dietary fat on its comparative feeding value in finishing diets for feedlot steers: metabolism

Six crossbred steers (315 kg) with cannulas in the rumen, proximal duodenum and distal ileum were used to study the influence of level and source of dietary fat on characteristics of digestion. Dietary treatments consisted of a steam-rolled barley-based finishing diet containing 1) no supplemental fat; 2) 4% yellow grease (YG); 3) 4% blended animal-vegetable fat (BVF); 4)8% YG; 5) 8% BVF or 6) 6% BVF and 2% crude lecithin. Increasing level of fat supplementation resulted in linear decreases (P less than .01) in ruminal and total tract digestion of OM and ADF and intestinal digestion of fat (P less than .05). At the 4 and 8% levels of supplementation, intestinal true digestibility of fat averaged 80.1 and 69.3%, respectively. Ruminal molar proportions of acetate decreased, and propionate molar proportion, as well as DE and ME values of the diet, increased linearly (P less than .01) with level of fat supplementation. The DE and ME values for fat were 8.17 and 9.76 at the 4% level and 7.35 and 8.72 Mcal/kg at the 8% level of supplementation, respectively. Yellow grease supplementation resulted in greater (P less than .05) ruminal fiber digestion and greater ruminal molar proportions of propionate than BVF. Intestinal fat digestion was similar (P greater than .10) for YG and BVF. Adding 25% lecithin to BVF resulted in greater ruminal fiber digestion and greater ruminal molar proportions of acetate; however, lecithin tended (P less than .10) to have a lower ME value than BVF.     

Effects of supplemental fat source on nutrient digestion and ruminal fermentation in steers

Five Holstein steers (235 kg of BW) fitted with ruminal, duodenal, and ileal cannulas were used in a 5 x 5 Latin square design experiment to determine the effects of supplemental fat source on site and extent of nutrient digestion and ruminal fermentation. Treatments were diets based on steam-flaked corn containing no supplemental fat (control) or 4% (DM basis) supplemental fat as tallow, dried full-fat corn germ (corn germ), corn oil, or flax oil. Fat supplementation decreased (P < 0.08) ruminal starch digestion but increased (P < 0.03) small intestinal starch digestion as a percentage of intake. Feeding corn germ decreased (P < 0.09) ruminal starch digestion and increased (P < 0.03) large intestinal starch digestion compared with steers fed corn oil. Large intestinal starch digestion was less (P < 0.04), and ruminal NDF digestion was greater (P < 0.09) for steers fed tallow compared with steers fed other fat sources. Small intestinal (P < 0.08) and total tract NDF digestibilities were greater (P < 0.02) for steers fed corn germ than for those fed corn oil. Feeding tallow increased total ruminal VFA (P < 0.03) and NH(3) (P < 0.07) concentrations compared with steers fed the other fat sources. Feeding corn germ led to a greater (P < 0.02) rate of ruminal liquid outflow compared with corn oil. A diet x hour interaction (P < 0.04) occurred for ruminal pH, with steers fed corn oil having the greatest ruminal pH 18 h after feeding, without differences at other time points. Fat supplementation increased (P < 0.09) ruminal concentrations of Fusobacterium necrophorum. Duodenal flow of C18:3n-3 was greater (P < 0.01) for steers fed flax oil compared with those fed corn oil. Feeding corn germ led to less (P < 0.01) ruminal biohydrogenation of fatty acids compared with corn oil. Steers fed tallow had greater small intestinal digestibility of C14:0 (P < 0.02) and C16:1 (P < 0.04) than steers fed the other fat sources. Fat supplementation decreased (P < 0.06) small intestinal digestibility of C18:0. Feeding corn germ decreased (P < 0.10) small intestinal digestibility of C18:1 compared with corn oil. It appears that source of supplemental fat can affect the site and extent of fatty acid and nutrient digestion in steers fed diets based on steam-flaked corn.     

Effect of cyclodextrin diallyl maleate on methane production, ruminal fermentation and microbes in vitro and in vivo

Effects of β‐cyclodextrin diallyl maleate (CD‐M) on methane production, ruminal fermentation and digestibility were studied both in vitro and in vivo. In in vitro study, diluted ruminal fluid (30 mL) was incubated anaerobically at 38°C for 6 and 24 h with or without CD‐M using hay plus concentrate (1.5:1) as a substrate. The CD‐M was added at different concentrations (0, 1.25, 2.5, 5.0 and 7.5 g/L). The pH of the medium and numbers of protozoa were not affected by the addition of CD‐M. Total volatile fatty acids were increased and ammonia‐N was decreased, molar proportion of acetate was decreased and propionate was increased (P < 0.05) by CD‐M. Methane was inhibited (P < 0.05) by 14–76%. The effect of CD‐M on methane production and ruminal fermentation was further investigated in vivo using four Holstein steers in a cross‐over design. The steers were fed Sudangrass hay and concentrate mixture (1.5:1) with or without CD‐M (2% of feed dry matter) as a supplement. Ruminal proportion of acetate tended to decrease and that of propionate was increased (P < 0.05) 2 h after CD‐M dosing. Total viable counts, cellulolytic, sulfate reducing, acetogenic bacteria and protozoa were unaffected while methanogenic bacteria were decreased (P < 0.05) by CD‐M. The plasma concentration of glucose was increased, whereas that of urea‐N was decreased (P < 0.05). Methane was inhibited (P < 0.05) from 36.4 to 30.1 L/kg dry matter intake by the addition of CD‐M. Apparent digestibilities of dry matter and neutral detergent fiber were not affected while that of crude protein was increased (P < 0.05) in the medicated steers. These data suggested that dietary supplementation of CD‐M decreased methane production and improved nutrient use.     

Effect of feeding frequency on forage fiber and nitrogen utilization in sheep

Four crossbred wether lambs (38 kg) with permanent ruminal and abomasal cannulae were used in a 4 X 4 Latin square arrangement of treatments to determine the effect of feeding frequency (FF) on forage fiber and N utilization. Lambs were offered 900 g of good quality (vegetative) Kentucky-31 tall fescue hay in equal portions either 2, 4, 8 or 16 times daily. Water consumption increased (P less than .05; linear) with increased FF. Apparent total tract digestibilities of dry matter, organic matter and cell wall constituents were not affected (P greater than .05) by FF, but apparent total tract digestibility of crude protein decreased (P less than .05; linear) with increased FF. Ruminal and post-ruminal digestion of acid detergent fiber (percent of total tract digestion) differed (P less than .05; cubic) among FF treatments. Although N retention was not affected (P greater than .05) by FF, increased FF decreased (P less than .05; linear) mean ruminal ammonia-N concentrations. Both the quantity of total N reaching the abomasum and the efficiency of microbial crude protein synthesis tended to increase (P greater than .05) with increased FF. In addition, the daily quantity of microbial N reaching the abomasum was affected (P less than .05; cubic) by FF. Ruminal pH was not affected (P greater than .05) by FF, whereas total volatile fatty acid concentrations (VFA) decreased (P less than .05; linear) with increased FF. Responses in molar proportions of individual VFA to FF were variable, and suggest that increasing FF elicits significant changes in the distribution of fermentation end-products.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dietary forage proportion on digestive function in maintenance-fed beef cows. Fescue and bermudagrass hays

Five crossbred beef cows (Hereford x Angus, 428 kg), cannulated in the rumen and duodenum, were used in a Latin square experiment to determine the effects of dietary proportions of fescue (F) and bermudagrass (B) hays (0:1, .25: .75, .5:.5, .75: .25 and 1:0) on digestive function. Feed intake was 85% of ad libitum intake of F alone (1.04% of body weight). Fescue contained 1.19% nitrogen (N), 74.8% neutral detergent fibre (NDF) and 6.3% acid detergent lignin (ADL), and B contained 1.99% N, 84.5% NDF and 6.1% ADL. Ruminal ammonia-N decreased and four- and five-carbon fatty acid concentrations increased linearly (P less than .05) with increasing F. Mean particle size of duodenal digesta was not affected by F level, but specific gravity of duodenal particles changed quadratically (P less than .05) as F rose, being greatest with 25 and 50% F. Ruminal fluid volume was constant, but dilution rate increased linearly (P less than .05) as F increased. Passage rate of B was faster than that of F in mixed diets. Organic matter (OM) flow and digestibilities, true ruminal N disappearance and microbial efficiency were not affected (P greater than .10) by F. True ruminal N disappearance and microbial efficiency were not affected (P greater than .10) by F. True ruminal N disappearance ranged from 73 to 78%, and microbial growth efficiency was between 18 and 22 g microbial N/kg OM fermented. Ruminal digestibilities of NDF, acid detergent fibre (ADF), cellulose and hemicellulose decreased linearly (P less than .05) as F increased, being 68.2, 64.9, 65.6, 61.2 and 61.6% for NDF, 58.9, 54.7, 56.2, 53.3 and 53.2% for ADF, 64.7, 61.3, 62.1, 59.0 and 59.1% for cellulose, and 76.1, 74.4, 75.4, 70.1 and 72.2% for hemicellulose for 0, 25, 50, 75 and 100% F, respectively. Digestive function in beef cows fed mixed F-B diets at a low level of intake related directly to dietary forage proportions and digestive characteristics when forages were fed alone.     

Effect of grain processing and silage on microbial protein synthesis and nutrient digestibility in beef cattle fed barley-based diets

Effects of the extent of grain processing and the percentage of silage in barley-based feedlot diets on microbial protein synthesis and nutrient digestibility were evaluated using four steers (initial BW of 442 +/- 15 kg) with ruminal and duodenal cannulas. The experiment was a 4 x 4 Latin square with four periods of 21 d each. Dietary treatments were arranged as a 2 x 2 factorial with two levels of barley silage (20 and 5% DM basis) and two degrees of barley grain processing (coarsely and flatly steamrolled to a processing index [PI] of 86 and 61%, respectively). The PI was quantified as the volume weight of the barley grain after processing, expressed as a percentage of the volume weight prior to processing. Digest a flow (Yb) and microbial (15N) markers were continuously infused into the rumen for a period of 13 d. Ruminal, duodenal, and fecal samples were collected at various times over the last 6 d of marker infusion. Diurnal ruminal pH was measured for 48 h. Intake of DM averaged 1.8% of BW, and was not different among the dietary treatments (P > 0.10). Ruminal starch digestibility was higher (P < 0.05) for the more extensively processed grain and tended (P < 0.10) to be highest when the more extensively processed grain was combined with 5% barley silage. In contrast, ruminal fiber digestibility for the 5% silage diets was reduced (P < 0.05) when the grain was more extensively processed. There was, however, no effect of grain processing on ruminal OM digestibility (P > 0.10), and hence, no inhibitory effect on microbial N flow to the intestine (P > 0.10). There was also no effect of the level of silage on microbial N flow (P > 0.10), but there was a tendency for improved efficiency of microbial protein synthesis for the 20% silage diets (P = 0.072). Ruminal escape of nonmicrobial N (P = 0.003) was greater, and thus, protein flow to the intestine was greater for the 5% silage diets. Diurnal ruminal pH was lower (P < 0.05) for 11 of the 24 hourly time points in steers fed the 5% silage diets than those fed the 20% silage diets. In conclusion, barley grain rolled to a PI of 86 to 61% and combined with 20 and 5% barley silage had little effect on microbial protein supply. Microbial protein supply was not inhibited when the barley grain was extensively processed (PI of 61%) and the silage was limited to only 5% of the diet DM, but feed intake of steers in this study was lower than would be expected in the feedlot.