Digestion In Steers Research Articles

Effects of saturation and esterification of fat sources on site and extent of digestion in steers: ruminal fermentation and digestion of organic matter, fiber, and nitrogen.

Five steers (average 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), 3) partially hydrogenated tallow (PHT), 4) hydrogenated tallow (HT), 5) blend (1:1) of HT and hydrogenated free fatty acids (HTHFA), and 6) hydrogenated free fatty acids (HFA). 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 (average 9 kg/d). Ruminal pH and molar proportion of propionate (P) were greater (P < .05) but total VFA concentration, proportion of acetate (A), A:P, and percentages of OM digested in the rumen and total tract were less (P < .05) when fat-supplemented diets were fed than when the control diet was fed. Total VFA concentration increased linearly (P < .05) as esterification of fat sources increased (HFA < HTHFA < HT). Acetate and A:P increased linearly (P < .10) but propionate and apparent total tract digestibility of OM decreased linearly (P < .05) as either saturation (T < PHT < HT) or esterification of fat sources increased. Ruminal NH3 N concentration increased linearly (P < .001) as saturation increased. Apparent ruminal digestibilities of ADF (P < .05) and NDF (P < .10) increased linearly as esterification increased. Flow of nonammonia nonmicrobial N to the duodenum was less (P < .10) but flow of microbial N was greater (P < .05) for the control diet than for fat-supplemented diets. Flows and small intestinal digestibilities of N and efficiencies of microbial protein synthesis were not altered by degree of saturation or esterification. Results confirm previous in vitro observations that T or HFA can alter ruminal digestion; however, because these effects usually are not observed in dairy cows, feed intake likely is very important in responses to supplemental fats.

Ruminal undegradability of blood meal and effects of blood meal on ruminal and postruminal digestion in steers consuming vegetative orchardgrass hay.

Four crossbred steers (360 +/- 3 kg) cannulated at the rumen and duodenum were used in a 4 x 4 Latin square design to examine the effects of supplemental blood meal (BM) on voluntary intake, digesta kinetics, ruminal fermentation, site and extent of digestion, and bacterial protein synthesis in steers fed vegetative orchardgrass hay (Dactylis glomerata L.). The levels of BM supplementation were 0, .07, .13, and .20 kg/d. Voluntary intake of OM (8.35 kg/d) was not significantly affected by BM supplementation. No significant effects of BM supplementation were detected for OM flow to the duodenum or digestion in the rumen or lower tract. However, total tract OM digestibility decreased 2.2 percentage units at .20 kg/d of BM intake (lower with vs without BM; P < .10). Total N intake and flow to the duodenum linearly increased (P < .10) with increasing BM level from 251 to 277 g/d and from 158 to 199 g/d, respectively. Ammonia N and bacterial N flows to the duodenum were not affected (P > .10) by BM supplementation. As a result, nonammonia N flow to the duodenum increased linearly (P < .10) with increasing BM supplementation. Ruminal escape N from BM was 83.5, 85.3, and 87.2% for .07, .13, and .20 kg/d of BM, respectively. Apparent bacterial efficiency and true bacterial efficiency were not affected (P > .10) by BM supplementation. Total amino acid and total essential amino acid flows to the duodenum were increased (P < .10) by dietary inclusion of BM. Duodenal flows of all essential amino acids except lysine and valine and of all nonessential amino acids except alanine and proline were increased (P < .10) by BM inclusion in the diet. In summary, supplementation with BM increased ruminal escape N and duodenal flows of total and most essential amino acids.

The effect of cereal carbohydrate supplementation on intake, rumen fermentation characteristics and digestibility in steers fed on grass silage

Synchronising the availability of energy and nitrogen to the rumen microbes is considered to be important for enhancing output of microbial protein from the rumen. This is particularly relevant to diets based on grass silage (Chamberlain and Choung, 1995). In the rumen ammonia, is rapidly released from the substantial content of non-protein nitrogen compounds in grass silage and this requires a similarly rapid release of energy in the rumen to ensure efficient capture of ammonia. Different sources of carbohydrate may enhance rumen function to varying degrees. The aim of this study was to examine the effects of various carbohydrate sources on intake, rumen fermentation characteristics and digestibility in steers fed on grass silage.

The effect of freezing and thawing grass silage on chemical composition and liveweight gain, intake, rumen fermentation characteristics and digestibility in steers

In many research situations it is useful to store silage frozen for use in future experiments. However, previous studies using fresh grass have demonstrated that freezing and thawing induces changes in the chemical composition of the herbage (Beever et al., 1974; MacRae et al., 1975). Of particular importance are the reductions in nitrogen and increases in carbohydrate solubility. The situation with grass silage is uncertain. The aim of this study was to examine the effect of freezing and thawing grass silage on intake, liveweight gain, rumen parameters and digestibility in steers.

The effect of cereal carbohydrate supplementation on intake, rumen fermentation characteristics and digestibility in steers fed on grass silage

Synchronising the availability of energy and nitrogen to the rumen microbes is considered to be important for enhancing output of microbial protein from the rumen. This is particularly relevant to diets based on grass silage (Chamberlain and Choung, 1995). In the rumen ammonia, is rapidly released from the substantial content of non-protein nitrogen compounds in grass silage and this requires a similarly rapid release of energy in the rumen to ensure efficient capture of ammonia. Different sources of carbohydrate may enhance rumen function to varying degrees. The aim of this study was to examine the effects of various carbohydrate sources on intake, rumen fermentation characteristics and digestibility in steers fed on grass silage.

The effect of freezing and thawing grass silage on chemical composition and liveweight gain, intake, rumen fermentation characteristics and digestibility in steers

In many research situations it is useful to store silage frozen for use in future experiments. However, previous studies using fresh grass have demonstrated that freezing and thawing induces changes in the chemical composition of the herbage (Beever et al., 1974; MacRae et al., 1975). Of particular importance are the reductions in nitrogen and increases in carbohydrate solubility. The situation with grass silage is uncertain. The aim of this study was to examine the effect of freezing and thawing grass silage on intake, liveweight gain, rumen parameters and digestibility in steers.

The influence of the basal diet on the effects of yeast culture on ruminal fermentation and digestibility in steers

The effects of dietary inclusion of yeast culture (Yea-Sacc) on rumen fermentation and digestibility in vivo were examined. In a Latin square experiment with 30-day periods, four rumen fistulated steers were offered 0 or 10 g yeast culture per animal daily in a low quality (4 kg barley straw plus 2.5 kg barley/soyabean meal mixture per day) (L) or high quality (2 kg barley straw plus 8 kg barley/soyabean meal mixture per day) (H) diet. The diets were offered in two feeds at 08:00 h and 16:00 h with no refusals. Rumen samples were withdrawn on 2 days per period at 08:00 (before feeding), 12:00, 16:00, 20:00 and 24:00 h. Mean rumen pH, liquid outflow rate, molar acetate proportion and the acetate to propionate ratio were lower ( P < 0.001) and the concentrations of total volatile fatty acids (VFA), ammonia and bacterial nitrogen and molar proportions of butyrate and isoacids were higher ( P < 0.001) on Diet H. Rumen ammonia concentration was not affected when yeast was included in Diet L but was reduced ( P < 0.05) when yeast was added to Diet H. Inclusion of yeast culture in Diet L decreased ( P < 0.05) VFA 4 h after the second feed, but inclusion of yeast culture in Diet H increased ( P < 0.1) VFA subsequent to the second feed. Degradability of cotton was lower on Diet H, but unaffected by yeast culture. In a replicated Latin square experiment with 34-day periods, 12 non-fistulated steers were offered the experimental diets. Digestibility of dry matter, organic matter and crude protein (CP) were higher ( P < 0.001) and acid detergent fibre lower ( P < 0.05) on Diet H. Digestibility of CP was decreased ( P < 0.05) when yeast was included in Diet L, but not affected when yeast was added to Diet H. It is concluded that dietary inclusion of yeast culture had a small influence on rumen fermentation parameters and in vivo digestibility, but that its effect on nitrogen metabolism appeared to be dependent on the nitrogen content of the basal diet.

Effect of a yeast culture ( Saccharomyces cerevisiae) on neutral detergent fiber digestion in steers fed oat straw based diets

The effect of Saccharomyces cerevisiae (SC) yeast culture (0 or 10 g day −1) on neutral detergent fibre (NDF) digestion of three mixed diets containing on a dry matter (DM) basis, 40, 60 and 80% oat straw (OS) has been studied with Holstein steers (251 ± 32 kg initial body weight (BW)) fitted with ruminal cannulae, in a 6 × 6 Latin square with a 3 × 2 factorial arrangement of treatments. No interaction was found between oat straw level and SC. In situ NDF digestibility (72 h incubation) increased linearly (37.9, 58.2 and 67.6%; P < 0.01) with increasing OS level and also with SC addition (48.6 vs. 60.45%; P < 0.08). pH hours below 6 decreased (5.3, 3.4 and 1.6 h; P < 0.01) with OS, but there was no SC effect ( P > 0.1). Volatile fatty acid (VFA) concentration was not affected by treatment ( P > 0.1); however, acetate molar percentage increased with OS levels (54.6%, 59.6%, 63.3%; P < 0.01) and decreased with SC addition (60.3 vs 58.0%; P < 0.07), whereas propionate molar percentage was reduced by OS (22.3%, 19.2% and 16.2%; P < 0.01) and increased by SC (20.7 vs 22.2%; P < 0.06). Ruminal protozoa population (organisms ml −1) showed a quadratic response (205802, 413329 and 274415; P < 0.01) to OS levels and it was increased by SC addition (254135 vs 341763; P < 0.01). Fractional rate of digesta passage was not changed by treatments ( P > 0.1). Dry matter intake showed a quadratic response to OS level (8.7, 9.1 and 7.5 kg day −1; P < 0.02), but there was no SC effect ( P > 0.1). Addition of a yeast culture with Saccharomyces cerevisiae improved NDF digestibility and propionate molar percentage; it also increased ruminal protozoa population, which could partially explain NDF digestibility changes.

Effects of hybrid and ensiling with and without a microbial inoculant on the nutritional characteristics of whole-plant corn

Two corn hybrids (Pioneer 3377 and 3389) with similar total plant and grain yield characteristics were evaluated to determine potential differences in nutritive value of the whole plant and stover. Hybrids were grown in plots at four different locations in Idaho in 1988 and 1989 for laboratory evaluation. Samples from the plots were stored fresh or ensiled with or without a microbial inoculant for 60 d in laboratory silos. Whole-plant samples of 3377 had a lower (P < .01) percentage of NDF (42.7 vs 48.1), ADF (26.3 vs 30), hemicellulose (16.2 vs 18.2), cellulose (21.4 vs 24), and lignin (3.4 vs 3.8). Similar differences, but of larger magnitude, were observed in stover samples. Ruminal in situ (24 h) and two-stage IVDMD of whole-plant and stover samples were greater (P < .01) for 3377 than for 3389. Lower fiber content and greater degradability for 3377 was not due to greater grain content; 3377 actually had numerically lower grain as a percentage of whole plant than 3389 (41 vs 44). Ensiling reduced (P < .05) NDF, hemicellulose, and cellulose content compared with fresh samples; however, no effect (P > .10) due to inoculant was noted. Hybrid x storage interactions were not observed (P > .10). Inoculation and hybrid did not affect (P > .10) organic acid concentration of the silages. In 1989 silages from 3377 and 3389 were harvested to evaluate diets containing 65% (DM basis) corn silage in steer digestion and growth trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prolonged thermal exposure on heat production, reticular motility, rumen-fluid and -particulate passage-rate constants, and apparent digestibility in steers

Six steers fitted with permanent rumen cannulae and fed alfalfa-grass hay were kept at either −10, 10 or 28 °C for 21 d to evaluate the effects of prolonged thermal exposure on heat production (HP) and digestive responses. HP was lowest at 28 °C and increased significantly (P &lt; 0.05) as the temperature was reduced to −10 °C. The duration of the biphasic reticular contraction during resting was significantly (P &lt; 0.05) reduced at −10 °C (5.4 s) compared with that at 10 °C (5.7 s) and 28 °C (5.7 s) whereas duration and amplitude of biphasic reticular contractions during rumination were elevated at −10 °C (P &lt; 0.05). Apparent digestibilities of dry matter, organic matter, neutral detergent fibre and crude protein on average were 11% (range 9–16%) higher (P &lt; 0.05) at 28 than at 10 °C. The particulate passage-rate constant was higher at −10 °C (P &lt; 0.05) than at 10 and 28 °C (0.046 vs. 0.038 and 0.034, respectively). The fluid passage-rate constant showed a quadratic response to temperature and was inversely related to digestibility. This study suggests that thermal exposure not only affects rumen particulate and fluid kinetics but also influences the form and pattern of reticular contractions. Further, the temperature-induced changes in duration and amplitude of reticular contractions during rumination were associated with changes in particulate passage-rate constants. Key words: Environmental temperature, reticulum, motility, fluid and particulate passage rates, digestibility, steer

Effect of formaldehyde-treated barley or escape protein on the ruminal environment and digestion in steers

Six Holstein steers fitted with ruminal and duodenal cannulae were fed three diets: formaldehyde-treated rolled barley (0.11% wt wt−1) with canola meal (FTB); untreated rolled barley supplemented with corn distillers' grain and fishmeal (EPB); and untreated rolled barley with canola meal (CON). Foam production from ruminal fluid did not differ among diets. Mean viscosity of ruminal fluid from steers fed FTB was lower (P &lt; 0.02) than rumen fluid from steers fed CON. Ruminal fluid pH of steers fed FTB was lower 2 h after feeding than in steers fed the EPB or CON diets. FTB led to lower (P &lt; 0.02) ruminal ammonia concentrations 1 and 2 h after feeding and lower (P &lt; 0.1) plasma urea nitrogen concentrations 4 h after feeding compared to EPB or CON diets. FTB and EPB tended to lower the ruminal concentration of volatile fatty acids (VFA) associated with microbial amino acid metabolism. Intake, ruminal and postruminal digestion of DM, OM, starch and NDF were not influenced by diet. While EPB had no effect on total tract digestion, FTB increased (P &lt; 0.1) total tract digestibility of starch and decreased (P &lt; 0.1) the digestibility of NDF. EPB increased (P &lt; 0.05) the supply of dietary protein and decreased the supply of microbial protein reaching the small intestine. FTB did not increase the amount of total nitrogen or starch reaching the small intestine of steers. Key words: Cattle, escape protein, starch, formaldehyde, barley

Protein and fiber digestion by steers grazing winter annuals and supplemented with ruminal escape protein.

Six abomasally cannulated Hereford steers (12 mo of age, 300 +/- 10 kg) grazing annual ryegrass (Lolium multiflorum Lam.) paddocks were used in a replicated 3 x 3 Latin square design to determine effects of ruminal escape protein (EP) supplementation on forage intake, fiber digestion, and protein flow to the intestine. Steers were fed one of three isoenergetic supplements: high ruminal escape protein (HEP), low ruminal escape protein (LEP), or corn, which supplied an estimated .25, .125, or 0 kg of EP/d in addition to EP supplied by corn. Fish meal (FM) and distiller's dried grains with solubles (DDGS) were sources of EP; FM provided 66.7% and DDGS provided 33.3% of estimated EP. Steers were adjusted to each supplement for 7 d before a 4-d collection period. Both total and forage DMI responded quadratically (P less than .03 and P less than .07, respectively) to EP supplementation. Total tract DM digestion tended (P less than .13) to increase linearly with EP supplementation. Abomasal total CP flow increased linearly (P less than .10) as supplemental EP increased. Crude protein flow in steers receiving HEP, LEP, and corn was 1,137, 1,027, and 844 g/d, respectively. Likewise, abomasal nonammonia N (NAN) tended to be greater (P less than .15, linear) for steers receiving HEP. Nonammonia N flows were 1,044, 955, and 771 g/d for steers receiving HEP, LEP, and corn, respectively. Abomasal ammonia flow did not differ (P less than .20) among treatments, nor did reticuloruminal fiber digestion (P less than .20). These data indicate that EP can increase postruminal protein flow and will not negatively affect fiber digestion in steers grazing annual ryegrass pastures.

Mixtures of wheat and high-moisture corn in finishing diets: feedlot performance and in situ rate of starch digestion in steers

Wheat and high-moisture corn (HMC) were fed singly and in three combinations using dry-rolled wheat (DRW) (ratios of 75:25, 50:50, and 25:75, respectively, Trial 1), or singly and in two combinations using steam-rolled wheat (SRW) (ratios of 67:33 and 33:67, respectively, Trial 2) to finishing beef cattle fed a high-concentrate diet. In situ rate of starch digestion (Trial 3) was measured on grains used in Trial 1 (excluding the 25 HMC: 75 DRW mixture) and ground dry corn. In Trial 1 (132 d), gain/feed did not differ (P greater than .10); however, final weight, hot carcass weight, and ADG decreased linearly (P less than .05) and DMI exhibited a cubic response (P less than .05) as the percentage of wheat in the diet increased. Carcass characteristics were not different. In Trial 2 (113 d), there were no differences attributable to treatment for ADG, DMI, gain/feed, or carcass characteristics. Positive associative responses for gain efficiency (gain/feed) were greatest for the first increment of wheat addition (25% DRW and 33% SRW in Trials 1 and 2, respectively) and for the early portion of the feeding period (57 and 28 d for Trials 1 and 2, respectively), indicating a more rapid diet adaptation and(or) less propensity for subacute acidosis. In Trial 3, the treatment grains or mixtures did not differ in rate of starch digestion. Although the differences were not statistically significant, starch in the 100% wheat diet was digested twice as fast as the 100 or 75% HMC mixtures.(ABSTRACT TRUNCATED AT 250 WORDS)

Digestion in steers and lactational performance of Jersey cows fed diets varying in natural protein level continuously or on alternate days

Five crossbred beef steers (515 kg) were used in a Latin square experiment and 36 lactating Jersey cows (12 primiparous, 310 kg; 24 multiparous, 365 kg) were used in a completely randomized design study to determine effects on characteristics of digestion and lactational performance of daily alternation of the dietary level of natural protein (NP). In Experiment 1, steers were fed diets of 50% bermudagrass hay and 50% concentrate. Concentrate was approximately 18% crude protein (CP), formulated to be 60, 80 or 100% NP (varying proportions of soybean meal, urea and ground corn), and was fed at 1.5% body weight (dry matter basis). These concentrates were fed daily or ones with 60 and 100% NP were fed on alternate days. Alternate day feeding did not markedly affect characteristics of digestion, including ruminal escape of feed protein, and NP level of concentrate fed continuously had no effects either. In Experiment 2, cows were subjected to treatments similar to those in Experiment 1, and performance on d 20-40 of lactation was measured. Concentrate was given at 1 kg (as fed)/2.15 kg milk produced, yielding a dietary concentrate level of approximately 40% (dry matter basis). Alternate feeding depressed (P less than 0.05) overall milk fat percentage. Alternate feeding increased production of milk and protein and body weight of primiparous cows but caused little change with multiparous cows. Besides increasing the dietary level of concentrate, perhaps alternate feeding regimes have utility to lower milk fat level without impairing milk production. Level of NP in concentrate fed continuously did not affect performance by multiparous cows though primiparous cow performance was generally enhanced, possibly because CP intake was adequate for multiparous cows but marginal for primiparous cows. However, overall, efficiency of production of solids-corrected milk rose slightly with increasing NP.

Small intestinal starch digestion in steers: effect of various levels of abomasal glucose, corn starch and corn dextrin infusion on small intestinal disappearance and net glucose absorption.

Eight Holstein steers (four at 300 kg, four at 406 kg) fitted with an elevated carotid artery, hepatic portal and mesenteric venous catheters, and abomasal and ileal cannulas were used in several 4 x 4 Latin square experiments to evaluate small intestinal starch digestion. They were fed alfalfa hay at 1.5% of BW and abomasally infused with water or glucose, corn starch or corn dextrin (one carbohydrate per Latin square) at 20, 40 or 60 g/h, with subsequent determination of small intestinal disappearance and net portal glucose absorption. Increasing the amount of all three carbohydrates infused abomasally increased the amount of carbohydrate disappearing in the small intestine. Increased infusion of glucose caused a continual increase (linear, P less than .01) in net glucose absorption, whereas net glucose absorption for starch and dextrin was maximal at the 20 g/h infusion (quadratic, P less than .05). With the 60 g/h infusion, 94% of the glucose but only 38% of starch and 29% of small intestinal dextrin disappearance could be accounted for as net glucose absorption, leaving a large portion of starch and dextrin disappearance unaccounted for. Of the infused starch and dextrin passing the ileum, 5.8 and 7.3%, respectively, was unpolymerized glucose, indicating that, at least in the distal small intestine, complete starch hydrolysis exceeded the capacity for glucose disappearance. It is concluded that only about 35% of the raw corn starch disappearing in the steer's small intestine resulted in net portal glucose absorption.

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.

Influence of soybean meal and sorghum grain supplementation on intake, digesta kinetics, ruminal fermentation, site and extent of digestion and microbial protein synthesis in beef steers grazing blue grama rangeland.

Six beef steers (British x Brahman) cannulated at the rumen, duodenum and ileum (avg wt 334 kg) and three mature steers (British x British) cannulated at the esophagus were used in a replicated 3 x 3 latin square design and fed no supplement (C), .5 kg soybean meal (SBM) or .5 kg steam-flaked sorghum grain (SFS).head-1.d-1 (DM basis) while grazing blue grama rangeland. Periods of the latin square included a minimum of 14 d for adaptation and 11 d for esophageal masticate collection and digesta sampling. In September, October and November, respectively, forage collected by esophageally cannulated steers averaged 74.5, 88.8 and 71.0% grasses; 2.06, 1.53 and 1.77% N and 68.3, (P greater than .10) by treatment, but total N intake was greater (P less than .05) for SBM vs C and SFS treatments. No differences (P greater than .10) were detected among treatments in OM, NDF, ADF and N digestibilities in the rumen, small intestine or hindgut, but total tract OM digestibility was greater (P less than .10) for SBM and SFS than for C, and total tract N digestibility was greater (P less than .10) for SBM than for C or SFS. Duodenal ammonia N flow was greater (P less than .05) when SBM was fed that when SFS and C were fed, but microbial N and non-ammonia, non-microbial N flows and microbial efficiency were not altered by treatment. Likewise, ileal N flow was not affected (P greater than .10) by treatment. Particulate passage rate, gastrointestinal mean retention time, forage in vitro OM disappearance and in situ rate of forage NDF digestion also were not affected (P greater than .10) by treatments. Ruminal fluid volume was greater (P less than .05) for SFS vs SBM and C treatments, but no differences were noted in fluid dilution rate. Ruminal fluid ammonia concentration was greater (P less than .05) when SBM was fed than when SFS and C were fed (13.5, 9.9 and 8.7 mg/dl, respectively), whereas pH and total VFA concentrations were not different (P greater than .10). Proportion of acetate in ruminal fluid was less (P less than .10) for SBM and SFS than for C. Small amounts of supplemental SBM and SFS had little effect on forage intake, ruminal fermentation and site of digestion but both increased total tract OM digestion in steers grazing blue grama rangeland.

Small intestinal starch, dextrin, and glucose digestion in steers (1988)

Three Holstein steers (930 lb) were surgically fitted with abomasal and ileal cannulae, portal and mesenteric venous catheters, and an elevated carotid artery and used to study small intestinal starch digestion. Water, corn starch (66 g/hr), corn dextrin (66 g/hr), or glucose (66 g/hr) were continuously infused into the abomasum. Small intestinal disappearance of corn dextrin (57 g/hr) and glucose (57 g/hr) were higher (P<.05) than that of starch (48 g/hr). The percentage of carbohydrate disappearance accounted for as net portal glucose flux was 52, 54, and 72% for corn starch, corn dextrin, and glucose, respectively. Small intestinal starch utilization in the bovine may be limited by starch granular characteristics, enzyme activity, and glucose transport across the small intestine.; Dairy Day, 1988, Kansas State University, Manhattan, KS, 1988;

Effects of supplement sulfate (Dynamate) and thiamin-HCl on passage of thiamin to the duodenum and site of digestion in steers.

Effects of dietary supplementation of thiamin-HCl (1 g daily) and a feed grade double sulfate of magnesium and potassium (Dynamate, added at 1.8% of diet dry matter; referred to as sulfate) on ruminal passage of thiamin and site of digestion in dairy steers (464 kg initial weight) fed a 77% concentrate diet were determined in a 4 X 4 Latin square experiment. Sulfate supplementation tended to reduce duodenal thiamin flow with (P less than .08) and without (P greater than .10) added thiamin. Supplementation with thiamin alone decreased ruminal disappearance of fed organic matter and nitrogen (P less than .03) and total tract disappearance of starch (P less than .06) and nitrogen (P less than .02), and increased ruminal microbial efficiency (P less than .04). Sulfate addition to the high thiamin diet alleviated these effects but depressed microbial efficiency (P less than .05). Sulfate included in the diet without added thiamin affected plasma thiamin positively, whereas sulfate added to the diet with supplemental thiamin changed plasma thiamin negatively (interaction, P less than .06). In conclusion, a marked depression of ruminal digestion induced by dietary thiamin-HCl supplementation disappeared upon dietary addition of sulfate and sulfate depressed the quantity of thiamin passing from the rumen. Because preventing thiamin deficiency and optimizing site of digestion in feedlot cattle are desired, these changes deserve further study.

Effects of Feed Intake and Protein Degradability on Ruminal Characteristics and Site of Digestion in Steers

Four multiple-fistulated Hereford steers were used in a 4×4 Latin square design with a 2×2 factorial arrangement of treatments [two intakes (9.1 and 6.1kg dry matter/d) and two protein sources differing in ruminal degradability (dry distillers grains and dry corn gluten feed)]. Steers fed at the high intake had faster fluid dilution rates (7.63 versus 6.52%/h), higher ruminal fluid outflows (120.2 versus 91.7 L/d), lower apparent ruminal digestibilities of organic matter (41.3 versus 44.3%) and neutral detergent fiber (56.0 versus 60.2%), and lower total tract digestibilities of neutral detergent fiber (64.3 versus 68.7%) than when they were fed at the low intake. Steers fed dry corn gluten feed had higher apparent ruminal digestibilities of organic matter (45.5 versus 40.1%) and neutral detergent fiber (60.2 versus 56.0%) and lower duodenal flows of nonammonia-nonbacterial N (40.1 versus 52.2% of N intake) than when they were fed dry distillers grains. Efficiency of ruminal bacterial growth was higher when steers were fed at the high versus low intakes. Efficiency of ruminal bacterial growth and site and extent of fiber digestion, especially hemicellulose, but not ruminal escape of protein, can be readily altered by manipulation of feed intake of moderately high forage diets.