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.     

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

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

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

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

Comparative feeding value of steam-flaked corn and sorghum in finishing diets supplemented with or without sodium bicarbonate.

A feedlot growth-performance trial involving 64 yearling steers and a metabolism trial involving four steers with cannulas in the rumen, proximal duodenum, and distal ileum were conducted to evaluate the comparative feeding value of steam-flaked corn (SFC, density = .30 kg/liter) and sorghum (SFS, density = .36 kg/liter) in finishing diets supplemented with or without .75% sodium bicarbonate (BICARB). No interactions between BICARB and grain type proved to be significant. Supplemental BICARB increased ADG 5.9% (P less than .10) and DMI 4.6% (P less than .05) but did not influence (P greater than .10) the NE value of the diet. Supplemental BICARB increased ruminal pH (P less than .01) and total tract fiber digestion (P less than .05). Differences in ruminal and total tract OM, starch, and N digestion were small (P greater than .10). Replacing SFC with SFS decreased (P less than .05) ADG 6.1% and increased (P less than .01) DMI/gain 9.7%. Corresponding diet NEm and NEg were decreased (P less than .01) 7.0 and 9.3%, respectively. Ruminal digestion of OM and starch tended to be lower (11.8 and 7.2%, respectively, P less than .10) for SFS. Ruminal degradation of feed N was 31% lower (P less than .05) for the SFS diets. Total tract digestibility of OM, N, DE, and ME were 3.3, 10.8, 4.4, and 5.5% lower (P less than .05), respectively, for the SFS vs SFC diets. In conclusion, 1) SFS had 92% the NEm of SFC; 2) differences in total tract starch digestibility were small and cannot explain the higher feeding value of SFC; 3) the low ruminal degradation of sorghum N (roughly 20%) should be considered in diet formulation to avoid a deficit in ruminally available N; and 4) .75% BICARB supplementation increased DMI and ADG of cattle fed highly processed grain-based diets.     

Impact of corn vitreousness and processing on site and extent of digestion by feedlot cattle

Eight cannulated Holstein steers (average BW: 251 kg) were used in 2 simultaneous 4 x 4 Latin squares in a split-plot arrangement to test the effects of processing method [dry-rolled (DR) vs. steam-flaked (SF); main plot] and vitreousness (V, %; subplot) of yellow dent corn (V55, V61, V63, and V65) on site of digestion of diets containing 73.2% corn grain. No vitreousness x processing method interactions were detected for ruminal digestion, but ruminal starch digestion was 14.4% lower (P < 0.01) for DR than for SF corn. Interactions were detected between vitreousness and processing method for postruminal (P < 0.10) and total tract digestion (P < 0.05). With DR, vitreousness tended to decrease (linear effect, P < 0.10) postruminal OM and starch digestion. With SF, vitreousness did not affect (P > or = 0.15) postruminal digestion of OM and starch. Postruminal N digestion tended to decrease (linear effect, P = 0.12) as vitreousness increased. Postruminal digestion was greater for SF than for DR corn OM (25.7%, P < 0.05), starch (94.3%, P < 0.10), and N (10.7%, P < 0.01). Steam flaking increased total tract digestion of OM (11%, P < 0.05), starch (16%, P < 0.01), and N (8.4%, P < 0.05) but decreased total tract ADF digestion (26.7%, P < 0.01). With DR, total tract starch digestion was lower for V65 (cubic effect, P < 0.10) than for the other hybrids. With SF, total tract starch digestion was not affected (P > or = 0.15) by vitreousness. Fecal starch and total tract starch digestion were inversely related (starch digestion, % = 101 - 0.65 x fecal starch, %; r2 = 0.94, P < 0.01). Ruminal pH was greater for steers fed DR than for steers fed SF corn (6.03 vs. 5.62, P < 0.05). Steam flaking decreased (P < 0.01) the ruminal molar proportion of acetate (24%), acetate:propionate molar ratio (55%), estimated methane production (37.5%), and butyrate (11.3%, P < 0.05). There was a vitreousness x processing interaction (P < 0.01) for acetate:propionate. For DR, acetate:propionate tended to increase (linear effect; P < 0.10) with increasing vitreousness. With SF, acetate:propionate was greater (cubic effect, P < 0.01) for V65. Starch from more vitreous corn grain was less digested when corn grain was DR, but this adverse effect of vitreousness on digestion was negated when the corn grain was SF. Of the 19% advantage in energetic efficiency associated with flaked over rolled corn grain, about 3/4 can be attributed to increased OM digestibility, with the remaining 1/4 ascribed to reduced methane loss.     

Influence of steaming time on site of digestion of flaked corn in steers

Four crossbred steers (395 kg) with cannulas in the rumen, proximal duodenum and distal ileum were used to evaluate effects of steaming time of corn on characteristics of digestion. The basal diet contained (DM basis) 12% forage-and 75% corn. The corn portion of the diet was provided as either dry-rolled (DR) or steam-flaked (SF), which had been exposed to steam for 34, 47 or 67 min prior to flaking to a mean density of .34 kg/liter. Longer steaming times linearly increased in vitro reactivity of corn starch to amyloglucosidase. Steaming time had a quadratic effect (P less than .05) on ruminal starch digestion. Ruminal starch digestibility of corn steamed for 47 min was 7% less than for corn steamed for 34 or 67 min. Longer steaming time linearly increased (P less than .05) flow of non-ammonia N to the small intestine with the principal increase (5.4%) between 34 and 47 min steaming time. Steaming time did not influence (P greater than .10) small intestinal or total tract digestibility of OM, starch or N. Compared with DR, SF increased (P less than .01) ruminal, small intestinal and total tract digestibility of starch 21.9, 75.1 and 9.2%, respectively. Although SF resulted in marked improvements in digestibility over DR, steaming times greater than 34 min were not beneficial.     

Influence of ruminal biohydrogenation on the feeding value of fat in finishing diets for feedlot cattle

Four Holstein steers (212 kg) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square experiment to study the influence of degree of ruminal biohydrogenation (BH) on the feeding value of supplemental fat. Treatments consisted of an 88% concentrate finishing diet supplemented with 1) 2% yellow grease (control); 2) 4% formaldehyde-protected fat (Rumentek), 2% yellow grease (LBH); 3) 2% Rumentek, 4% yellow grease (MBH); or 4) 6% yellow grease (HBH). Ruminal BH of HBH, MBH, and LBH diets was 74, 68, and 54%, respectively. High-fat supplementation decreased (7%, P < .05) intestinal digestibility of 18:0 but increased intestinal digestibility of 18:1 (3%, P < .10), 18:2 (14%, P < .01), and 18:3 (23%, P < .05). Increases in intestinal digestibility of 18:0 (quadratic effect, P < .05), 18:1 (linear effect, P < .01), 18:2 (linear effect, P < .01), 18:3 (linear effect, P < .05), and total fatty acids (linear effect, P < .05) were inversely related to BH. For every 1% increase in the proportion of 18:1 fat entering the small intestine, the digestibility of 18:0 increased 1%. High-fat supplementation depressed ruminal digestion of OM (11%, P < .05), NDF (16%, P < .05), starch (6%, P < .05), and feed N (12%, P < .01). Formaldehyde-protein protection of fat diminished its depressing effects on ruminal digestion of NDF (quadratic effect, P < .10) and enhanced ruminal escape of feed N (linear effect, P < .10). Postruminal digestion of OM was greater (4.6%, P < .10) for high-fat diets. High-fat diets decreased (P < .05) total tract digestion of OM (1.9%), NDF (7.4%), and starch (.5%). Postruminal and total tract digestibility of OM, NDF, N, and starch was not affected (P > .10) by BH. In a 125-d finishing trial, 100 yearling steers (362 kg) were used to evaluate treatment effects on growth performance. High-fat diets did not affect (P > .10) ADG but increased (P < .10) feed efficiency (9%, P < .10), dietary NEm (7.6%, P < .05), and dressing percentage (9%, P < .05). The magnitude of the increase in dressing percentage was inversely related (linear effect, P < .10) to BH. We conclude that decreasing ruminal BH will increase postruminal digestibility of fat, and hence the NE value of dietary fat. The synergistic effect of increasing the proportion of 18:1 on intestinal digestion of fat enables higher levels of fat supplementation. Protecting fat from BH minimizes the detrimental effects of supplemental fat on fiber digestion.     

Influence of flake density on the comparative feeding value of steam-flaked corn for feedlot cattle

Two trials were conducted to examine the influence of flake density (FD) on the feeding value of steam-flaked corn. Treatments consisted of corn that had been steam-flaked to mean densities of .42, .36 and .30 kg/liter (28, 24 and 20 lb/bu). In Trial 1, treatment effects on characteristics of digestion were evaluated using three crossbred steers with cannulas in the rumen and proximal duodenum. In Trial 2, treatment effects on feedlot performance were evaluated in a 112-d finishing trial involving 72 crossbred steers with an average initial weight of 312 kg. Flake density was directly related to flake thickness (P less than .01) and inversely related (P less than .01) to in vitro enzymatic digestibility of starch. Decreasing the FD resulted in a linear decrease (P less than .01) in ruminal pH and linear increases (P less than .05) in postruminal and total tract digestibility of starch. Postruminal digestibility of N and total tract digestibility of OM, N and energy also increased linearly (P less than .05) with decreasing FD. Flake density did not influence (P greater than .10) feedlot performance or carcass merit. There was a tendency (P greater than .10) for depressed rate and efficiency of gain for steers fed the 30 kg/liter FD corn. Improvements in digestibility and N utilization of SF corn-based diets as a result of decreasing FD from .42 to .30 kg/liter did not enhance feedlot performance. This may be due to digestive dysfunction, perhaps related to processing effects on ruminal pH.     

Supplemental cracked corn for steers fed fresh alfalfa: II. Protein and amino acid digestion

The effects of different levels of cracked corn on N intake, ruminal bacterial CP synthesis, and duodenal flows and small intestinal digestion of amino acids (AA) in steers fed fresh alfalfa indoors were determined. Angus steers (n = 6; average BW 338 +/- 19 kg) cannulated in the rumen, duodenum, and ileum were fed each of five diets over five periods in a Latin square design with an extra animal. Steers consumed 1) alfalfa (20.4% CP, 41.6% NDF) ad libitum (AALF); 2), 3), and 4) AALF supplemented (S) with three levels of corn (.4, .8, or 1.2% of BW, respectively), or 5) alfalfa restricted (RALF) to the average forage intake of S steers. Average N intake and duodenal flow of nonammonia N (NAN) were greater (P < .01) in S than in RALF steers. Greater duodenal flows of NAN in S compared with RALF were due to a trend toward higher (P = .06) flows of both bacterial and dietary N. Levels of corn decreased (P < .01) linearly N intake and increased (P < .01) linearly duodenal flow of NAN owing to a numerical linear increase in nonbacterial N (P = .15) with no increase in bacterial N flow. Duodenal NAN flows as percentages of N intake increased (P < .01) linearly (69.3 to 91.0%) as corn increased. Ruminal NH3 N concentration, ruminal CP degradability, and the proportion of bacterial N in duodenal NAN were decreased (P < .01) linearly as corn increased. Efficiency of net microbial CP synthesis was not affected (P > .05) by treatment (average 42.6 and 30.9 g N/kg of OM apparently or truly digested in the rumen, respectively). Small intestinal disappearance of total N and individual AA, except for threonine and lysine, and small intestinal digestibility of N and individual AA, except for methionine, histidine, and proline, increased (P < .01) linearly with level of corn and were greater (P < .01) in S than in RALF steers. Supplementing corn to steers fed fresh alfalfa reduced ruminal N losses and CP degradability and increased the duodenal flow and the small intestinal disappearance and digestibility of total N and total, essential, and nonessential AA.     

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.     

Influence of endosperm vitreousness and kernel moisture at harvest on site and extent of digestion of high-moisture corn by feedlot steers

Six ruminally and duodenally cannulated Angus-Jersey crossbred steers (450 kg of BW) were used in a 6 x 6 Latin square to evaluate the effect of kernel vitreousness and moisture on intake and digestibility of high-moisture corn. Arranged in a 2 x 3 factorial, diets included a floury (FLO) or a vitreous (VIT) endosperm corn hybrid harvested at 28.1% (DRY), 31.2% (MID), or 35.7% (WET) kernel moisture content. Diet DM consisted of 88.25% high-moisture corn, 6% chopped alfalfa hay, 2% corn gluten meal, 0.75% urea, and 3% supplement. Supplement was included to ensure that the diets contained a minimum (DM basis) of 0.6% Ca, 0.6% K, 0.2% S, 33 mg/kg of monensin, and 11 mg/kg of tylosin. Geometric mean diameter of lyophilized high-moisture corn tended to be less (P = 0.06) for VIT than for FLO, and the calculated particle surface area was 15.8% greater (P = 0.03). An interaction of vitreousness with the quadratic effect of moisture was noted (P < 0.001), such that fraction a and effective degradation for starch tended to be greater for the vitreous hybrid at the least and greatest moisture content but lower for the vitreous hybrid at the intermediate moisture content. Intake and ruminal disappearance of DM, OM, and starch were not influenced by vitreousness or moisture, with ruminal starch disappearance averaging 90.9%. Intestinal starch digestion measured as a percentage of starch entering the intestines averaged 91% and was greater (P < 0.05) for VIT than FLO corn. Averaged across moisture levels, total tract starch digestibility was greater (P < 0.003) for VIT than FLO. Compared with FLO kernels, VIT kernels appeared to be more brittle and therefore shattered more readily when rolled, particularly at the driest kernel moisture level. Furthermore, increased surface area of smaller particles may have been responsible for the greater starch utilization from VIT corn. In contrast with the results from other in situ and in vivo trials with dry-rolled corn grain, in which the starch from vitreous hybrids was less rapidly or completely digested, hybrids with more vitreous starch, when fed as high-moisture corn, had greater total tract starch digestibility, primarily due to greater postruminal starch digestion.     

Effects of dietary nitrogen level and ileal antibiotic administration on digestion and passage rates in beef heifers. I. High-concentrate diets

Four beef heifers (211 kg) fitted with ruminal, duodenal and ileal cannulae (T-type), were fed a high-concentrate diet with a low (L) or high (H) level of N (1.71 and 2.18%, respectively), and received daily doses of either saline (S) or an antibiotic (A) mixture (2 g neomycin sulfate and .25 g bacitracin) into the terminal ileum in a 4 X 4 Latin-square experiment. Added N increased ruminal NH3-N concentration and tended to increase efficiency of microbial growth and to decrease ruminal disappearance of organic matter, starch and protein. Administration of antibiotics into the ileum reduced nucleic acid content of feces (P less than .05), tended to reduce digestion of organic matter and starch in the hindgut and total tract and increased ileal pH (P less than .05). Ileal administration of antibiotics increased ruminal escape of feed N by 26 and 42% with the low and high N diets, respectively, and increased ruminal passage rate of particulates. Ruminal N digestion was inversely related to ruminal particulate passage rate (r = -.49; P less than .06). Ruminal liquid passage rate was inversely related to rate of fluid passage through the hindgut and was reduced by ileal administration of antibiotics with the low N diet, but increased by antibiotics with the high N diet. Results indicate that administration of antibiotics into the terminal ileum alters digestive function earlier in the digestive tract including ruminal passage rates and digestion of N in the rumen. Responses were partially modulated by dietary N level.     

Evaluation of alfalfa-corn cob associative action. III. The effect of mechanically separated alfalfa fractions on intake, digestibility and ruminal characteristics of ammonia-treated corn cob diets fed to sheep

The influence of mechanically separated alfalfa fractions on intake, digestibility and rate of ruminal passage was investigated using 48 lambs (32 kg) in a digestion trial. Whole plant pre-bloom alfalfa (25% crude protein) or fractions (presscake, dehydrated presscake, protein coagulum, dehydrated protein coagulum, whole juice or deproteinized juice) were added to a 3% ammonia (NH3)-treated corn cob negative control diet at levels equal to 20% wholeplant alfalfa dry matter (DM); eight treatments, six lambs/treatment. Ad libitum intake was greater (P less than .05) for alfalfa fiber (presscake) or juice supplemented diets compared with 20% direct cut alfalfa. Dry matter intake, digestibility of DM and cell walls, and rate of passage were highly correlated when diets were fed ad libitum. At equal DM intakes, dehydrated vs wet presscake increased (P less than .05) DM and cell wall digestibility. Heating of the protein may have reduced degradation rate and consequently a slower release of nutrients for microorganisms in the rumen. Whole vs deproteinized juice increased digestibility of cob DM (P = .11) and cell walls (P = .13), suggesting a response to level of degradable alpha-amino N. Whole and deproteinized juice increased cell wall digestibility compared with the negative control by 23.0 and 18.5 percentage units, respectively, suggesting that degradable alpha amino-N and cell solubles or other nutrients interacted to maximize microbial fiber digestion. Total and branch-chain volatile fatty acids measured at 6, 12 and 18 h post-feeding were highly correlated with nutrient digestibility. Ruminal NH3-N measured at 18 h was negatively correlated with dry matter (r = -.74) and cell wall (r = -.72) digestibility, showing that alfalfa supplies nutrients required by ruminal microorganisms for NH3 assimilation and fiber digestion. The mode of alfalfa associative action in high fiber diets is in supplying ruminal microorganisms with degradable protein and (or) other nutrients, rather than altering ruminal retention time.     

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.     

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.     

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.     

Influence of alfalfa maturity on feed intake and site of nutrient digestion in sheep

Four wethers fitted with ruminal, duodenal and ileal cannulas were used to study effects of maturity of alfalfa hay on intake, digestion and rate of passage of nutrients in various sites of the digestive tract. Pre-, early-, and mid-bloom hays were harvested from the same field; full-bloom hay was acquired from elsewhere due to wether conditions. Dry matter intake decreased (P less than .05) as intakes of NDF and ADF increased. This was attributed to decreased digestibility and increased retention time of undigested residues. Digestion of OM in the stomach (% of intake) was 44.2, 47.4, 38.8 and 35.1 for pre-, early-, mid- and full-bloom hay, respectively. Digestion of ADF in the stomach was lower for mid-bloom than for pre-and early-bloom hay (P less than .05). Degradation of alfalfa protein in the rumen was 94, 88, 81 and 78% for pre-, early-, mid- and full-bloom hay, respectively. Concentration of ruminal NH3 N, flow of N at the duodenum, fecal N and urinary N decreased of the hay and to N intake. Digestion of N in the small intestine (g/d) decreased as maturity advanced (P less than .05). Duodenal flow of total amino acids was greater (P less than .05) when animals consumed pre-bloom hay than when they consumed more mature hays. Relative feed value calculated from the detergent fiber analysis correlated with actual value determined biologically (r = +.81). Intake and site of nutrient digestion of alfalfa hay were influenced by the stage of maturity at harvest.     

Inhibition of proteolysis at harvest using heat in alfalfa silages: effects on silage composition and digestion by sheep

Heat treatment at harvest was used to investigate the effects of proteolysis on silage composition and digestion by sheep. Four alfalfa (Medicago sativa) silages were prepared, two from mid-bloom and two from pre-bloom crops from the same field. Mid-bloom alfalfa was conserved with formic acid as two unwilted silages, either without (unwilted control; UWC) or after heat treatment (unwilted heated; UWH) applied as steam for 1 min. Pre-bloom alfalfa was ensiled either after 24 h wilting (wilted control; WC) or after heating in a crop dehydrator for 2 min (wilted control; WH). Heated treatments were inoculated with Lactobacillus plantarum. Eight wethers, cannulated in the rumen and duodenum, were given the silages to determine the effects of heat treatment on digestion. Heat treatment inhibited protease activity and reduced protein catabolism in the silo. In unwilted silages, heat treatment had no effects (P greater than .05) on OM or N digestion, but it reduced (P less than .05) CP degradability in the rumen. In wilted silages, heat treatment reduced (P less than .05) apparent OM digestion in the rumen and increased (P less than .05) the proportion of N intake flowing to the intestines as non-ammonia N (NAN). Efficiency of microbial protein synthesis also was increased (P less than .01). Absorption of N posterior to the duodenum was increased (P less than .05) in WH compared to WC, but there was no effect (P greater than .05) of heat treatment on apparent total tract N digestibility.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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)