Diet characteristics, digesta kinetics, and dry matter intake of steers grazing eastern gamagrass.

Eastern gamagrass (Tripsacum dactyloides [L.] L.) has attracted attention as a forage crop, but information on its use is lacking. This 2-yr study compared diet quality, ingestive mastication, and ADG by steers grazing eastern gamagrass (GG), flaccidgrass (Pennisetum flaccidum Griseb.), and Tifton 44 bermudagrass (Cynodon dactylon [L.] Pers.). The design was a randomized complete block with two agronomic replicates. The diet selected by steers from GG in May did not differ from the diet selected by steers from flaccidgrass (FG) for IVDMD (77.3%), NDF (44.0%), CP (19.5%), and mean and median particle sizes of the ingesta (1.8 and 1.4 mm). In July, GG diets had three percentage units less IVDMD (P less than .05), 8.4 percentage units more NDF (P less than .05), and 4.5 percentage units less CP (P = .07) than the mean of FG and bermudagrass (BG). The canopy (July) of GG had the greatest proportion of its DM as leaf (59 vs 26% for FG and 22% for BG) and the least proportion as stem (25 vs 40% for FG and 59% for BG). Mean particle size (millimeters) of masticates differed (P = .05) among forages with GG greatest (2.2), followed by FG (1.6), and BG particles were smallest (1.2). Proportion of large (greater than or equal to 2.8 mm), medium (less than 2.8 greater than or equal to .5 mm), and small (less than .5 mm) particles of the masticate DM, and their IVDMD and NDF concentration, interacted with species (P less than .05). Gamagrass masticate had the greatest proportion (28%) of large particles and BG the greatest proportion (23%) of small particles. The least IVDMD occurred for large particles of BG (62.5%) and small particles of GG (63.8%). Digesta kinetics did not differ among species. Characteristics of GG yielded steer ADG of .82 vs .67 kg for FG and .30 kg for BG (P = .05).     

Effects of corn vs corn gluten feed on site, extent and ruminal rate of forage digestion and on rate and efficiency of gain

Three digestion experiments and one growth experiment were conducted to determine site, extent and ruminal rate of forage digestion and rate and efficiency of gain by cattle offered alfalfa haylage supplemented with corn or dry corn gluten feed (CGF). In Exp. 1, eight steers were fed alfalfa haylage-based diets with substitution of corn for 0, 20, 40 or 60% of haylage in a 4 X 4 latin square. Increasing dietary corn substitution increased (P less than .05) OM, NDF and ADF digestion by steers but decreased (P less than .05) rate of in situ alfalfa DM digestion. In Exp. 2, five heifers were fed alfalfa haylage-based diets with increasing dietary levels of CGF in a 5 X 5 latin square. Increasing dietary CGF increased (P less than .05) OM, NDF and ADF digestion by heifers. In Exp. 3 and 4, cattle were fed alfalfa haylage-based diets containing either 20 or 60% corn or CGF. In Exp. 3, supplementation increased (P less than .05) OM and NDF digestion but level X supplement source interaction (P less than .05) occurred, with added CGF increasing OM and NDF digestion more than added corn. In Exp. 4, supplementation improved (P less than .05) DM intake, daily gain and feed efficiency. Dry matter intake and daily gain were greater (P less than .05) for 60% supplementation than for 20% supplementation. Overall, whereas increasing the level of dietary supplement increased (P less than .05) OM, NDF and ADF digestion, only corn addition decreased (P less than .05) rate of in situ alfalfa DM digestion. Daily gains and feed efficiencies were similar in cattle fed either corn or CGF with alfalfa haylage.     

Lysocellin effects on growth performance, ruminal fermentation, nutrient digestibility and nitrogen metabolism in steers fed forage diets

Studies were conducted to determine the effects of lysocellin on growth performance and metabolism of steers fed forage-based diets. Treatments in all experiments consisted of 1) control, 2) 100 mg lysocellin/d, 3) 200 mg lysocellin/d and 4) 200 mg monensin/d. In each of two 90-d performance studies, 24 Hereford steers were individually fed greenchop (fungus-free tall fescue and Coastal and Tifton-44 bermudagrass) ad libitum and .91 kg/d of a corn-trace mineral salt supplement. In Exp. 1, tall fescue was fed from d 1 to 45 and bermudagrass from d 46 to 90. Bermudagrass was offered during d 1 to 45 and tall fescue during d 46 to 90 in Exp. 2. Lysocellin improved gain (Exp. 1, P less than .01) and feed conversion (Exp. 1 and 2 combined, P less than .05), decreased total VFA concentrations (P less than .05), increased molar proportions of propionate, isobutyrate and isovalerate (P less than .01), decreased molar proportions of acetate and butyrate (P less than .01) and lowered acetate:propionate (P less than .01). Two metabolism studies involving a total of 16 Hereford steers were conducted. Steers were fed tall fescue greenchop and .91 kg/d supplement for a 34-d adjustment period followed by a 5-d total collection period. Lysocellin increased N digestibility (P less than .01) and N retention (P less than .06) but did not (P greater than .05) affect DM, NDF or ADF digestibility. Data indicate that lysocellin results in major alterations in ruminal fermentation and can increase growth performance and N retention in steers fed forage-based diets.     

Relationships of body weight, forage composition, and corn supplementation to feed intake and digestion by Holstein steer calves consuming bermudagrass hay ad libitum

Holstein steer calves (101 to 350 kg BW) consumed bermudagrass hay ad libitum without or with supplemental ground corn up to 1.0% of BW. As BW increased, total DMI increased quadratically (-2.459 + .05448 [BW]-.000073 [BW2] + .540 [corn DMI]; R2 = .83, sy.x = .655). Each kilogram of corn DM decreased bermudagrass DMI by .46 kg. Total digestible OM intake (kg) increased with BW and corn supplementation (.314 + .0127 [BW] + .441 [corn OM intake]; R2 = .79, sy.x = .444). Feed intake level accounted for approximately 2.5 times more variability in total digestible OM intake than digestion did. Corn supplementation decreased digestion of bermudagrass NDF (62.50 - 8.468 [corn DMI, % BW]; R2 = .13, sy.x = 8.121), with a similar decrease across BW. Increasing bermudagrass DMI (% of BW) decreased bermudagrass NDF digestion slightly, but variation accounted for was only 33% of that attributable to corn DMI (% of BW). Concentrations of common fiber fractions (NDF, ADF, cellulose, hemicellulose, and ADL) in bermudagrass explained very little variation in feed intake and digestion, indicating considerable influence of other factors. Bermudagrass intake and digestion were not related, and no substantial interactions were observed among steer BW, corn level, and bermudagrass composition.     

The interaction of harvesting time of day of switchgrass hay and ruminal degradability of supplemental protein offered to beef steers

The objective of this study was to evaluate an interaction between harvest at 0600 (AM) vs. 1800 (PM) with high (HI) or low (LO) ruminal degradability of a protein supplement to change voluntary intake, digestion, or N retention by steers offered switchgrass (Panicum virgatum L.) hay. Black steers (255 +/- 14 kg of BW) were blocked by BW, and then randomly assigned (5 steers each) to AM/HI, PM/HI, AM/LO, or PM/LO treatment groups. Steers were group-housed in covered, outdoor pens with individual feeding gates. After adaptation and standardization, intake was measured for 21 d followed by a digestion trial (5 d of total collection). Steers were offered 767 (LO) or 825 (HI) g/d of supplement to provide 268 g of CP/d. Compared with AM, PM had greater (P = 0.01) concentrations of total nonstructural carbohydrate (TNC, 71 vs. 56 g/kg of DM), and lesser concentrations of NDF (760 vs. 770 g/kg of DM, P = 0.02), ADF (417 vs. 427 g/kg of DM, P = 0.02), and CP (55.9 vs. 58.6 g/ kg of DM, P = 0.07). Protein fractions A, B(2), and B(3) were similar for AM and PM, but HI contained more (P < 0.02) A (694 vs. 296 g/kg of protein) and less B(2) (174 vs. 554 g/kg of protein) fraction than LO. Harvest interacted with supplement to increase (P = 0.07) ad libitum digestible DMI for steers offered PM/HI (11.4 g/kg of BW daily) compared with steers offered PM/LO (10.2 g/kg of BW daily), but there was no difference for steers offered AM/LO or AM/HI (10.7 g/kg of BW). Apparent digestibilities of DM (594 vs. 571 g/kg of intake), NDF (591 vs. 562 g/kg of intake), ADF (585 vs. 566 g/kg of intake), and N (651 vs. 632 g/kg of intake) were greater (P < 0.04) for PM than for AM. Apparent digestibility of N was greater (P = 0.02) for HI (652 g/ kg of intake) vs. LO (631 g/kg of intake). Interactions between harvest and supplement for apparent digestibilities of NDF (P = 0.09) and ADF (P = 0.03) were due to no change or an increase in digestibility in response to increased ruminal degradability of supplement in steers offered PM harvest, whereas increased ruminal degradability of supplement decreased digestibility of NDF and ADF in steers offered AM harvest. Treatments did not affect hay intake (3.93 kg/d), N retained (15.8 g/d), or plasma urea N (5.25 mM) during ad libitum intake. Greater TNC in PM vs. AM harvest was not sufficient by itself to increase total voluntary DMI, but greater protein degradability interacted with harvest time to increase ruminal fiber digestibility and digestible DMI of beef steers offered PM vs. AM harvest.     

Grazing selectivity and in vivo digestibility of switchgrass strains selected for differing digestibility

Animal selectivity and digestibility differences among switchgrass strains selected for different in vitro dry matter digestibilities (IVDMD) were measured in a grazing trial with esophageally fistulated steers and a sheep digestion trial. Extrusa selected by esophageally fistulated steers grazing high-IVDMD (Trailblazer), Pathfinder and low-IVDMD strains of switchgrass were compared, as were top and whole plant hand-clipped samples from each strain. Trailblazer extrusa had higher (P less than .1) in vitro organic matter disappearance (IVOMD) and lower (P less than .1) NDF and ADF than Pathfinder extrusa. Extrusa from all three strains appeared to be of higher quality than top or whole plant hand-clipped samples. In vitro organic matter disappearance tended to be highest for Trailblazer top hand-clipped samples. Composition of hand-clipped samples among strains was not significantly different. Mature crossbred wethers were used to compare Trailblazer and Pathfinder switchgrass hay in a digestion trial. No differences (P greater than .1) were detected between strains for DMI or apparent digestibility of DM, NDF, ADF and CP. Extrusa from Trailblazer switchgrass that had been selected for whole plant IVDMD had higher IVOMD; however, there was no indication that steers selected a differentially higher IVOMD for one strain than another.     

Effects of ammoniation of tall fescue on phenolic composition, feed intake, site and extent of nutrient digestion and ruminal dilution rates of steers

Tall fescue hay (H) supplemented with corn and urea (HU) or corn gluten meal (HCGM) and ammoniated tall fescue hay supplemented with corn (AH) or corn gluten meal (AHCGM) were fed to steers in two 4 X 4 Latin-square trials. Diets were fed to four Angus-Hereford steers (550 kg) at equal intakes in trial 1 and to four Hereford steers (350 kg) at ad libitum intakes in trial 2. Ammoniation reduced cell wall concentrations of p-coumaric acid and ferulic acid by 48 and 67%, respectively. Concentrations of other phenolics were also reduced. Apparent total tract digestibilities of vanillin, p-coumaric acid and ferulic acid were lower (P less than .05, .001 and .01, respectively) when nontreated hay was fed in trial 1, but were not different between hay types in trial 2. In trial 1, greater negative intestinal digestibilities of p-coumaric acid (P less than .001) and vanillin (P less than .05) occurred for steers fed HU and HCGM vs AH and AHCGM diets. Digestibilities of neutral detergent fiber (NDF) and acid detergent fiber (ADF) were greater (P less than .001) for steers fed ammoniated hay diets in both trials and greater (P less than .05) for HCGM vs HU in trial 1. More than 96% of the NDF and ADF digested by steers in trial 1 was digested in the stomach. Intakes of digestible NDF and ADF, but not indigestible NDF or ADF, were higher (P less than .001) for steers fed AH and AHCGM in trial 2. In situ dry matter disappearance rate of ammoniated hay was greater (P less than .05) than that of nontreated hay, but rate of cotton thread disappearance from bags suspended in the rumen of steers fed the various diets was similar among treatments. In both trials, feeding ammoniated hay resulted in higher (P less than .05) ruminal concentrations of acetate and higher (P less than 0.05) acetate:propionate ratios. Ruminal liquid dilution rates were lower (P less than .05) for steers fed AH and AHCGM in trial 1, but were not different in trial 2. Ruminal dry matter concentration and solids dilution rate were not affected by diet in either trial. The results are interpreted to indicate that increased intake of ammoniated hay is a result of increased rate and extent of fiber digestion.     

Effect of exogenous fibrolytic enzyme on ruminal fermentation and digestibility of alfalfa and rye-grass hay fed to lambs

This experiment was carried out to study the effect of a directly fed exogenous fibrolytic enzyme on intake and digestion of DM, OM, protein, NDF, ADF, and hemicellulose of alfalfa and ryegrass hay by sheep. Four diets were randomly assigned to four ruminally cannulated lambs using a 4 x 4 Latin square design, repeated in time, with a factorial arrangement (2 x 2) of diets: 1) alfalfa hay; 2) alfalfa hay + exogenous fibrolytic enzymes (enzyme); 3) ryegrass hay; and 4) ryegrass hay + enzyme. Lambs consumed more DM and OM from alfalfa than from ryegrass hay (P < 0.001). The ADF intake was not different between the hays, but NDF intake was lower for alfalfa (P < 0.001). For both hays, the enzyme increased intake of DM (P < 0.01), as well as OM and CP (P < 0.05); however, NDF and ADF intake were not changed. Alfalfa hay had higher apparent digestibility of DM, OM, and CP (P < 0.001), but lower digestibility for NDF, ADF, and hemicellulose. The enzyme increased apparent digestibility of CP, hemicellulose (P < 0.05), and NDF (P < 0.10) for alfalfa. Also, for both hays, the enzyme improved N balance because lambs retained more N (P < 0.05). The enzyme increased (P < 0.05) total VFA concentration (3 and 6 h) for both hays. Results from this trial indicate that directly fed exogenous fibrolytic enzymes may change ruminal fermentation, intake, and digestibility of forages with different nutritive value.     

The delivery of cottonseed meal at three different time intervals to steers fed low-quality grass hay: effects on digestion and performance

A ruminal fermentation trial and a steer growth trial were conducted to evaluate the effects of time interval of cottonseed meal (CSM) supplementation of predominantly meadow fescue grass hay (GH; CP = 6.6%) on nutrient digestion and growth performance of beef steers. The fermentation trial used four ruminally cannulated steers assigned to a 4 x 4 latin square design with dietary treatments of GH fed alone (C) or GH supplemented with 3 g CP/kg BW.75 daily as supplied by CSM every 12, 24 or 48 h. Nylon bags containing GH were inserted into the rumen on d 1 and 2 of each collection period and incubated for 12, 24, 48 and 96 h to measure NDF and ADF degradation. Subsequently, steers were fed Yb-labeled GH and fecal samples were collected to determine particulate passage rate (PR). Dry matter and NDF intake, mean NDF and ADF in situ disappearance and ruminal VFA concentrations were greater (P less than .05) when CSM was fed; however, the delivery of CSM at various times did not affect (P greater than .10) these variables. Supplemented diets tended (P = .08) to have faster PR compared with the C diet. In the growth trial, CSM supplemented steers consumed more digestible DM (P less than .05) and had greater (P less than .05) daily gain compared with C steers. Effects due to time of CSM supplementation were not observed for the variables measured in the present study.     

Effects of corn condensed distillers solubles supplementation on ruminal fermentation, digestion, and in situ disappearance in steers consuming low-quality hay

Two metabolism (4 x 4 Latin square design) experiments were conducted to evaluate the effects of corn condensed distillers solubles (CCDS) supplementation on intake, ruminal fermentation, site of digestion, and the in situ disappearance rate of forage in beef steers fed low-quality switchgrass hay (Panicum virgatum L.). Experimental periods for both trials consisted of a 9-d diet adaptation and 5 d of collection. In Exp. 1, 4 ruminally and duodenally cannulated steers (561 +/- 53 kg of initial BW) were fed low-quality switchgrass hay (5.1% CP, 40.3% ADF, 7.5% ash; DM basis) and supplemented with CCDS (15.4% CP, 4.2% fat; DM basis). Treatments included 1) no CCDS; 2) 5% CCDS; 3) 10% CCDS; and 4) 15% CCDS (DM basis), which was offered separately from the hay. In Exp. 2, 4 ruminally and duodenally cannulated steers (266.7 +/- 9.5 kg of initial BW) were assigned to treatments similar to Exp. 1, except forage (Panicum virgatum L.; 3.3% CP, 42.5% ADF, 5.9% ash; DM basis) and CCDS (21.6% CP, 17.4% fat; DM basis) were fed as a mixed ration, using a forage mixer to blend the CCDS with the hay. In Exp. 1, ruminal, postruminal, and total tract OM digestibilities were not affected (P = 0.21 to 0.59) by treatment. Crude protein intake and total tract CP digestibility increased linearly with increasing CCDS (P = 0.001 and 0.009, respectively). Microbial CP synthesis tended (P = 0.11) to increase linearly with increasing CCDS, whereas microbial efficiency was not different (P = 0.38). Supplementation of CCDS to low-quality hay-based diets tended to increase total DM and OM intakes (P = 0.11 and 0.13, respectively) without affecting hay DMI (P = 0.70). In Exp. 2, ruminal OM digestion increased linearly (P = 0.003) with increasing CCDS, whereas postruminal and total tract OM digestibilities were not affected (P > or = 0.37) by treatment. Crude protein intake, total tract CP digestibility, and microbial CP synthesis increased (P < or = 0.06) with increasing level of CCDS supplementation, whereas microbial efficiency did not change (P = 0.43). Ruminal digestion of ADF and NDF increased (P = 0.02 and 0.008, respectively) with CCDS supplementation. Based on this data, CCDS used in Exp. 2 was 86.7% rumen degradable protein. The results indicate that CCDS supplementation improves nutrient availability and use of low-quality forages.     

Influence of roughage source on kinetics of digestion and passage, and on calculated extents of ruminal digestion in beef steers fed 65% concentrate diets

Roughage sources were compared in flaked milo-based diets that contained 35% chopped alfalfa hay (AH, control diet) or with cottonseed hulls (CSH) or chopped wheat straw (WS) replacing half the AH. Latin square experiments were used to measure total tract digestion coefficients, particulate passage rates (rare earths), liquid turnover rates (Co-EDTA), and rumination time in six growing steers (Exp. 1) and in situ digestion of DM and NDF, ruminal pH and ruminal DM distribution in three mature, ruminally cannulated steers (Exp. 2). Rates of passage from Exp. 1 and rates and extents of digestion from Exp. 2 were used to calculate apparent extent of ruminal digestion (AED). In Exp. 1, total tract digestibilities of DM and NDF were lower (P less than .05) by 7 and 22%, respectively, when CSH, but not WS, were included in the diet. Digestibility of cell solubles was not different (P greater than .10) among diets. Inclusion of WS increased (P less than .10) rumination time by 36%, and CSH increased intake (P less than .10) by 17% over the control diet. In Exp. 2, there tended to be (P less than .20) increased in situ digestion of milo and AH in the WS diet. Measures of ruminal pH were similar for all diets. The AED for AH and milo DM and NDF, and the proportion of total tract NDF digestion occurring in the rumen (50, 47 and 62% for control, CSH and WS diets, respectively), were highest (P less than .05) for the WS diet. This resulted in similar total tract digestibilities for the WS and AH diets. The two low-digestibility roughages had different effects at this concentrate level; wheat straw enhanced apparent extent of ruminal digestion for NDF of other ingredients in the mixed diets, but cottonseed hulls did not.     

Effects of calendar date and summer management on the in situ dry matter and fiber degradation of stockpiled forage from bermudagrass pastures.

Limited information is available that describes the disappearance kinetics of bermudagrass (Cynodon dactylon L. Pers.) during fall and early winter. Five ruminally cannulated, crossbred steers (387 +/- 18.3 kg) were used to determine the effects of calendar date and previous summer management on the in situ degradation kinetics of DM and NDF for forage clipped from stockpiled 'Greenfield' bermudagrass pastures. Forage was stockpiled at two sites following summer hay or pasture management, and samples were taken outside (GRAZED) and under caged exclosures (UNGRAZED) at 4-wk intervals beginning October 17, 1997, and ending January 9, 1998. No effort was made to remove or avoid contaminate species. Concentrations of NDF increased (P < 0.001) to a maximum for UNGRAZED forages at the hay site between October 17 and December 12, but sampling date had no effect (P = 0.627) on concentrations of NDF at the pasture site. Concentrations of ADF and lignin increased (P < or = 0.023) during at least one sampling interval in UNGRAZED forages at both sites. At the hay site, degradation rates of DM decreased (P < 0.001) by 0.013/h for UNGRAZED forage between October 17 and January 9, whereas the effective ruminal degradability of DM decreased (P < 0.001) by 33.5% during the same time period. Fractional degradation rates of NDF for UNGRAZED forages at the hay site decreased (P < 0.001) by 0.014/h between October 17 and November 14 but did not change (P > or = 0.077) throughout the remainder of the study. The effective ruminal degradability of NDF decreased (P < 0.001) by 33.8% between the first and last sampling date. At the pasture site, sampling date did not affect (P = 0.458) rates of DM degradation, but the effective degradability of DM for UNGRAZED forages decreased (P = 0.001) by 19.0% from October 17 to December 12. Rates of NDF degradation for UNGRAZED forages did not differ (P > or = 0.113) on the first three sampling dates, but the rate on January 9 was slower than that observed on October 17 (P = 0.025) and November 14 (P = 0.044). The effective degradability of NDF decreased (P < 0.001) by 19.2% between October 17 and December 12. These data indicate that stockpiled bermudagrass should be used during a limited window during the late fall; after this time, the nutritive value becomes very poor.     

Technical note: sampling technique and drying method effects on chemical composition of tall fescue or fescue-ladino clover pasture samples

Although esophageal extrusa is the most readily accepted representation of forage consumed by grazing ruminants, esophageal sampling is demanding from the standpoint of animal care and maintenance and extrusa processing. This experiment was conducted with a split-plot design to evaluate the effects of pasture type, pasture sampling technique and drying method on estimation of grazed forage composition. Ten esophageally fistulated steers grazed pastures of either tall fescue (Festuca arundinacea Schreb.) or tall fescue interseeded with ladino clover (Trifolium repens L.); steers were closely observed during four collection periods to determine their exact grazing location. Forage samples were collected either directly from the esophageal fistula (E) or hand-gathered (HG) from the immediate perimeter of the grazed area. Samples of E and HG from each steer were divided and oven-dried at 40 degrees C or lyophilized. Fescue samples had lower (P less than .01) N and ADF N concentrations than fescue-ladino clover samples, and E-collected fescue samples had lower (P less than .05) in vitro digestible OM than E-collected fescue-ladino clover samples. Sampling x drying method interactions were detected (P less than .01) for OM, NDF, ADF, hemicellulose (HEMI), ADL, alkaline peroxide lignin (APL), ADFN and indigestible ADF (IADF). Oven-dried E had higher (P less than .05) NDF, ADF, HEMI, ADL, APL and ADF N than lyophilized E; ADF N and IADF were higher from oven-dried HG than from lyophilized HG. In vitro digestible OM was not modified by oven drying. Hand-gathered samples, whether lyophilized or oven-dried, did not simulate E dried by lyophilization. Standardized collection techniques and drying procedures should be implemented to minimize damage to fibrous components.     

Comparing relative feed value with degradation parameters of grass and legume forages

Relative feed value (RFV) was evaluated relative to in situ degradation parameters of grass and legume forages. Early-cut alfalfa (n = 20), late-cut alfalfa (n = 26), cool-season grass (n = 11), warm-season grass (n = 4), and grass-legume (n = 20) samples were collected from duplicate hay bales submitted to the 2002 and 2003 Missouri State Fair Hay Contests. Subsamples were incubated in the rumen of 2 lactating Holstein cows for 0, 6 or 8, 12, 24, and 48 h to determine in situ degradation of DM, ADF, NDF, CP, and hemicellulose over time. Degradation data were fit to a variety of candidate models to estimate degradation parameters. Correlation coefficients between degradation parameter estimates [sorted according to forage (early-cut alfalfa, late-cut alfalfa, grass, or grass-legume)] and RFV were determined. For further comparison, correlations between NDF degradation parameter estimates and digestible DMI were determined with data from a previous study. Degradation data were best fit to a single, gamma 2-distributed pool model without a lag phase. Relative feed value was significantly correlated (P < 0.05) with potentially digestible DM and CP for early-cut alfalfa, potentially digestible DM for late-cut alfalfa, and potentially digestible DM, NDF, and hemicellulose for grass-legume. The percentage of significant correlations (10.7%) across the entire data set was low and no correlations were significant for grass. Relative feed value did not account for the variation in degradation parameters, especially for grasses. A further correlation analysis, which compared digestible DMI with degradation parameter estimates reported from another data set, revealed that digestible DMI and degradation parameter estimates were related for grass but not for alfalfa forages. These results suggest that RFV is limited by its failure to include degradation parameters.     

Estimation of feeding value of four tropical forage species at two stages of maturity

The feeding value of four tropical grasses was assessed through voluntary intake and digestibility studies using yearling Brahman x British steers (average BW = 256 +/- 34 kg). The digestibility of OM was estimated using total fecal collection (TFC), in vitro OM digestibility (IVOMD), and by estimating fecal production using insoluble acid detergent fiber (IADF) as an indigestible marker. The four grasses consisted of bahiagrass (Paspalum notatum), limpograss (Hemarthria altissima), bermudagrass (Cynodon dactylon), and stargrass (Cynodon spp.). Grass was harvested at two stages of maturity (approximately 4 and 10 wk). Forages were ground (5 to 10 cm) and offered to steers ad libitum. Forage treatments were assigned randomly to steers over eight 28-d periods and repeated over two consecutive years. Total forage offered and refused was determined during a 14-d sample collection period. For determination of fecal output, steers were placed into metabolism crates for 7 d. Composited samples of forage offered, forage refused, and feces of each steer at each period were analyzed for DM, OM, NDF, ADF, IADF, IVOMD, and CP. All digestibility results were calculated on an OM basis. There were year x grass x maturity interactions (P < 0.01) for all measures of forage quality, except CP. Increased maturity resulted in a 37.8% decrease (P < 0.001) in CP concentration when averaged across all forages. Four-week bermudagrass contained the greatest (P < 0.05) concentration of CP compared with all other grasses at both maturities, except 4-wk stargrass. Bahiagrass IVOMD did not differ among 4- and 10-wk maturities in both years; however, the IVOMD content of both stargrass and bermudagrass decreased (P < 0.05) when these forages matured from 4 to 10 wk. Apparent OM digestibility, determined by TFC, was greater (P < 0.05) than OM digestibility determined by IVOMD and IADF for all forages except bahiagrass, for which IADF did not differ from TFC. In Year 1, OM intake (OMI) of 10-wk limpograss was less (P < 0.05) than all other 4-wk forages. In Year 2, voluntary OMI of 10-wk limpograss was less (P < 0.05) than all grass x maturity combinations, except for 10-wk bermudagrass. These data suggest that important differences exist in changes in nutrient quality associated with increased maturity in tropical forages. Among the forages assessed in this study, bahiagrass seems to better retain nutrient quality when maturing from 4 to 10 wk.     

Effects of supplemental alfalfa hay on feed intake and digestion by Holstein steers consuming high-quality bermudagrass or orchardgrass hay

Effects of level and frequency of supplementation with alfalfa (A) on feed intake and digestion by steers fed bermudagrass (B) or orchardgrass (O) were determined in two Latin square experiments. In Exp. 1, six Holstein steers (224 kg) were fed B (2.25% N; 71.4% NDF) or O (2.52% N; 64.3% NDF) with 0, 15 or 30% (DM) A (2.70% N; 44.0% NDF). Total DMI was 2.43, 2.72 and 2.85% BW for B and 2.98, 3.00 and 2.87% BW for O with 0, 15 and 30% A, respectively. Total DMI was affected by forage (P less than .05), A level (linear; P less than .06) and a forage x A level (linear) interaction (P less than .05). Digestible OM intake increased .42 (15%) and .67 kg (24%) with feeding of 15 and 30% A, respectively, for B, but for O, only dietary inclusion of 30% A elevated digestible OM intake (.14 kg and 4% increases). In Exp. 2, five Holstein steers (165 kg) were fed B (1.81% N; 78.6% NDF) alone or with A (2.76% N; 52.8% NDF). Morning meals consisted of ad libitum B (OA), .3% BW of A daily (.3A), .6% BW of A every 2nd d (.6A), .9% BW of A every 3rd d (.9A) or 1.2% BW of A every 4th d (1.2A). All steers received B in the afternoon ad libitum, and B was given in the morning when A was not fed. Total DMI was 2.31, 2.12, 2.12, 2.26 and 2.29% BW for OA, .3A, .6A, .9A and 1.2A, respectively (SE .049). Grass characteristics affected response in feed intake to legume supplementation. Frequency of dietary legume addition may alter feed intake.     

Effects of supplemental degradable intake protein on utilization of medium- to low-quality forages

Three independent experiments were conducted each using 16 ruminally fistulated beef steers fed bermudagrass (8.2% CP, 71% NDF; Exp. 1), bromegrass (5.9% CP, 65% NDF; Exp. 2), or forage sorghum (4.3% CP, 60% NDF; Exp. 3) hays to evaluate the effects of increasing level of supplemental degradable intake protein (DIP) on forage utilization. In each experiment, steers were blocked by weight and assigned to one of four treatments, and hay was offered to each steer at 130% of average voluntary intake for the preceding 5-d period. Supplemental DIP (sodium caseinate) was placed in the rumen at 0700, immediately before feeding forage. Levels of DIP supplementation were .041, .082, and .124% BW; the control received no supplemental DIP. Following a 10-d adaptation, intake and total fecal output were measured for 7 d. In Exp. 1, neither forage OM intake (FOMI) nor fiber (NDF) digestion were influenced (P > or = .20) by increasing level of DIP supplementation. The DIP supplied by the bermudagrass hay was estimated to be 8.2% of the total digestible OM intake (TDOMI) for control steers. In Exp. 2, increasing level of supplemental DIP did not affect (P > or = .26) FOMI but tended to increase total OM intake linearly (TOMI; P = .10). The tendency for a rise in TOMI coupled with a slight numeric increase in digestion resulted in an increase (linear; P = .06) in TDOMI. In the treatment group in which the maximum TDOMI was observed (supplemental DIP treatment of .082% BW), total DIP intake constituted approximately 9.8% of the TDOMI. In Exp. 3, FOMI, TOMI, organic matter digestion (OMD), and TDOMI were improved (P < .01) by increasing amounts of supplemental DIP. Although there was some evidence of a tendency for a decrease in the magnitude of change in TDOMI in response to increasing DIP supplementation, a clear plateau was not achieved with the levels of supplement provided. When the highest level of supplemental DIP was fed, DIP constituted approximately 12.8% of the TDOMI. In conclusion, significant variation was observed among forage in the amount of DIP needed to maximize intake and digestion when expressed in relationship to the digestible OM.     

Effects of supplement type on animal performance, forage intake, digestion, and ruminal measurements of growing beef cattle

Two experiments were conducted to determine the effects of supplement type on the rate of gain by heifers grazing bermudagrass and on the intake, apparent total-tract OM digestibility, ruminal fermentation, digesta kinetics, in situ DM digestibility, and forage protein degradation by steers fed prairie hay. In Exp. 1, 45 heifers (284+/-24 kg) grazed a bermudagrass pasture for 91 d in the late summer to determine the effects of no supplement (CON), or one of four individually fed monensin-containing (150 mg/[heifer x d]) supplements (MINCS; 0.1 kg of mineral mix with 0.2 kg [DM] of cottonseed hulls as a carrier/[heifer x d]), a pelleted protein supplement (PROT; 1 kg of DM, 242 g of degradable intake protein [DIP]/[heifer x d]), or high-fiber (HF) and high-grain (HG) (2 kg of DM, 243 and 257 g of DIP, respectively/[heifer x d]) pelleted energy supplements. In Exp. 2, four ruminally cannulated steers (311+/-22 kg) with ad libitum access to low-quality (4% DIP, 73% NDF, 40% ADF) prairie hay were individually fed monensin-containing (200 mg/[steer x d]) treatments consisting of 1) mineral mix + corn (MINCR; 0.1 kg of mineral and 0.4 kg of cracked corn [DM] as a carrier, 19 g of DIP/[steer x d]), 2) PROT (1.4 kg of DM, 335 g of DIP/[steer x d]), 3) HF, or 4) HG (2.9 kg of DM, 340 and 360 g of DIP, respectively/[steer x d]) in a 4 x 4 Latin square with 14-d adaptation and 6-d sampling periods. In Exp. 1, the HF-, HG-, and PROT-supplemented heifers had greater (P < 0.01) rates of gain than CON heifers, and the HF- and HG-supplemented heifers tended (P < 0.11) to gain more weight than those fed PROT. In Exp. 2, steers fed PROT consumed more (P < 0.05) hay OM than HF and HG, or MINCR. Total OM intake was greater (P < 0.01) by supplemented steers than MINCR-fed cattle. Hay OM digestibility was not affected (P = 0.19) by treatment, but total diet OM digestibility was greater (P < 0.01) for HF- and HG- than for MINCR- or PROT-fed steers. The rate of in situ DM digestibility was greater (P < 0.01) for HF, HG, and PROT than for MINCR. Results from these studies indicate that feeding milo- vs fiber-based energy supplements formulated to provide adequate DIP did not result in different forage intake, OM digestibility, or in situ DM digestibility, whereas both increased ADG in heifers consuming low-quality forages compared with unsupplemented or mineral- or protein-supplemented cattle. An adequate DIP:TDN balance decreased the negative associative effects often observed when large quantities of high-starch supplements are fed with low-quality hay.     

Effects of diet concentrate level and sodium bicarbonate on site and extent of forage fiber digestion in the gastrointestinal tract of wethers

Four adult wethers (45 kg) with permanent ruminal and abomasal cannulae were used in a repeated measures Latin-square arrangement of treatments to quantitate the effects of diet concentrate level and sodium bicarbonate (NaHCO3) on site and extent of forage fiber digestion in the gastrointestinal tract. Experimental diets consisted of Kentucky-31 tall fescue hay, soybean meal and a semi-purified concentrate mixture in ratios of 95:5:0, 76:4:20, 57:3:40 and 38:2:60; NaHCO3 represented 0 or 7.5% of the concentrate mixture. Ruminal digestion (% of intake) of neutral detergent fiber (NDF) and hemicellulose decreased linearly (P less than .05), whereas acid detergent fiber (ADF) digestion responded in a cubic (P less than .05) fashion to increasing concentrate level; NaHCO3 improved ruminal digestion of NDF (P less than .10) and ADF (P less than .05), but not hemicellulose. Post-ruminal digestion (% of rumen non-degraded) of NDF and ADF tended to increase, whereas hemicellulose digestion responded in a cubic (P less than .05) fashion to increasing concentrate level; NaHCO3 decreased (P less than .05) post-ruminal digestion of all fiber fractions. Total tract digestion of NDF and ADF showed a cubic (P less than .05) response, whereas hemicellulose digestion responded in a quadratic (P less than .05) fashion to increasing concentrate level; NaHCO3 had no effect on total tract digestion of any fiber fraction. Correlations of ruminal hemicellulose digestion with mean pH (r = .33; P = .07) and minimum pH (r = .30; P = .09) were attained in a 24-h feeding cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of alfalfa maturity on energy utilization by cattle and nutrient digestibility by cattle and sheep.

Two comparative slaughter experiments conducted with growing beef steers (300 kg to 480 kg BW) fed alfalfa cubes demonstrated that animal performance diminished as alfalfa matured. In each trial, ADG (empty BW basis) was 10 to 20% greater from pre-bloom than from early-bloom alfalfa. Net energy for maintenance (Mcal/kg) followed a pattern similar to that of ADG, but NEg (Mcal/kg) did not decrease (P greater than .05) as alfalfa maturity increased. Digestion trials with steers and wethers clearly indicated significant reductions in apparent digestibilities of DM, energy, and cell wall fractions as alfalfa matured. Steers fed at 110% of maintenance in digestion Trails 1, 2, and 3 consistently digested cubed alfalfa to a greater extent than wethers fed the same alfalfa ground and pelleted. Digestion coefficients (percentages) for ADF, cellulose, NDF, and crude fiber were 5 to 14% greater for steers fed cubes than for wethers fed pellets. Regression equations calculated from results of three digestion trials indicate that digestible DM % and DE (Mcal/kg) could be predicted from ADF %, but they were 4 to 5% lower for wethers fed pelleted alfalfa than for steers fed cubes.