Effects of Supplement Strategy on Intake and Digestion of Prairie Hay by Beef Steers and Plasma Amino Acid Concentrations1

56

Greenwood al. The Professional AnimaletScientist 14:56–61

of Supplement Strategy on Effects Intake and Digestion of Prairie Hay by Beef Steers and Plasma Amino Acid Concentrations1,2 R. H. GREENWOOD, E. C. TITGEMEYER, C. A. LÖEST, and J. S. DROUILLARD Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS 66506-1600

Abstract

those steers assigned to the control treatment (2.4 kg/d). Although RPM increased plasma methionine concentrations (P<0.05), it was ineffective in stimulating forage intake or digestion. In summary, supplementation with a cooked molasses block increased digestible OM intake by increasing forage intake and digestion, whereas corn supplementation depressed forage intake but nonetheless increased total digestible OM intake.

content, but this can be improved by addition of degradable intake protein (11). Producers commonly use corn Twelve steers (373 kg initial BW) to provide supplemental energy or were used in three simultaneous 4 × 3 molasses-based blocks to supply incomplete Latin squares to evaluate the supplemental N and energy to effects of supplemental corn (1.8 kg/d, animals fed low-quality forages. 0.14 kg CP/d), cooked molasses block Feed intake may be depressed by (0.45 kg/d, 0.14 kg CP/d), and rumenelevated plasma histidine concentraprotected methionine (RPM; 3.5 g DLtions (16). One possible explanation methionine/d) on intake and digestion of for increased plasma histidine is a prairie hay (5.7% CP, 72.3% NDF on deficiency of methionine. During DM basis). Steers that consumed the regeneration of methionine from cooked molasses block ate more (P<0.05) (Key Words: Cattle, Forage, Supplehomocysteine, free tetrahydrofolate, forage OM (7.0 kg/d) and those fed mentation, Digestion, Intake.) which is required for histidine supplemental corn ate less (P<0.05) catabolism, is regenerated. Thereforage OM (5.5 kg/d) than control steers fore, an inadequate supply of me(6.2 kg/d). Total OM intake was higher thionine may limit histidine catabo(P<0.05) for steers consuming the corn lism, thereby increasing plasma (7.0 kg/d) and cooked molasses block Intake of forage (hay or pasture) histidine concentrations and depress(7.3 kg/d) than for control animals (6.2 by ruminants often is depressed ing feed intake. kg/d). Digestible OM intake was lower when the crude protein content of The objectives of this study were (P<0.05) for steers assigned to the the forage is below 6 to 7% (6). to evaluate the effects of three control treatment (3.1 kg/d) than for Depressed forage intake decreases different supplement strategies [corn, steers consuming the cooked molasses available energy and decreases cooked molasses block, and block (3.9 kg/d) or corn (3.6 kg/d). animal performance. Available ruminally protected methionine Digestible NDF intake was higher energy to the animal can be in(P<0.05) for steers assigned to the creased directly by supplying supple- (RPM)] on intake and digestion of prairie hay by beef cattle and plasma molasses block treatment (2.9 kg/d) and mental energy in the form of starch lower (P<0.05) for steers assigned to (20) or indirectly by increasing forage amino acid concentrations. supplemental corn (2.0 kg/d) than for intake with supplemental protein (7). The amount of energy in a forage that will be available to an animal is 1Contribution No. 98-91-J, Kansas Agric. Exp. a function of the quality and ruminal During the fall and early winter of Sta., Manhattan, KS. microbial fermentation of the forage. 1996, 12 British and British-cross Microbial fermentation is hindered steers (373 kg initial BW) were used Sponsored by W. P. Flatt. when a forage has a low protein in three simultaneous 4 × 3 incomReviewed by N. A. Cole and K. Coffey.

Introduction

Materials and Methods

57

Supplementation of Prairie Hay

plete Latin squares, which were developed to equalize carryover effects among treatments. Steers were housed in an open-front barn in individual 1.4 × 6.8 m pens with continuous lighting. Tallgrass-prairie hay (Table 1) and water were available for ad libitum intake. Experimental treatments (as-fed) were 1) control, no supplement; 2) 1.8 kg/d supplemental corn that provided 0.14 kg CP/d; 3) 0.45 kg/d supplemental cooked molasses block that provided 0.14 kg CP/d; and 4) 5.0 g/d supplemental Smartamine™M (Rhône-Poulenc Animal Nutrition, Atlanta, GA), a RPM product that provided 3.5 g DL-methionine/d. Chemical compositions of supplements are reported in Table 1. All steers received 20 g/d white salt, and the RPM was mixed with the salt. The cooked molasses block was provided in small pieces so that it could be consumed rapidly. Steers received the supplements at 0600 h just before forage was fed. Forage, which had been coarsely chopped to pass through a 76-mm screen, was offered at 115% of the average consumption for the previous 5 d. Collections. There were three experimental periods of 21 d each. Steers were allowed to adapt to treatments for 14 d. Representative forage and supplement samples were collected on d 13 to 19, and orts were collected on d 14 to 20. Steers were fitted with fecal bags to allow for

total fecal collection during the final 7 d of each period. Feces were removed and weighed daily to determine output; a 2% subsample was collected for later analysis. At 0630 h on d 21 of each period prior to offering supplements, 10 mL of jugular blood were collected by venipuncture into vacutainer tubes containing sodium heparin (Becton Dickinson, Franklin Lakes, NJ) and placed on ice until further processing in the laboratory. Forage and corn samples were dried at 50 °C in a forced-air oven for 48 h. Daily fecal samples were mixed, subsampled, and dried at 50 °C in a forced-air oven for 96 h. Airequilibrated (48 h) forage, corn, and fecal samples were weighed and then ground to pass a 1-mm screen. Laboratory Analysis. Dietary ingredients, orts, and fecal samples were analyzed as follows: DM by drying samples for 24 h at 100 °C; OM and ash by placing dried sample in a muffle oven for 12 h at 460 °C; NDF by the procedures of Van Soest et al. (23); and N by the Kjeldahl method (1). The DM of the cooked molasses block was analyzed by drying samples for 12 h at 70 °C in a vacuum oven. Samples of the corn and cooked molasses block were prepared and analyzed for mineral content according to AOAC (1). The cooked molasses block was analyzed for sugar content as follows: extraction in 50% ethanol solution con-

TABLE 1. Chemical composition of tallgrass-prairie hay and supplements. Nutrient

Prairie hay

Corn

Blocka

RPMb

DM

86.5

87.6

95.8

99.9

92.3 72.3 5.7

(% of DM) 98.6 13.6 8.9

71.4 8.3 32.3

99.9 NDc 46.6

OM NDF CP aCooked

molasses block. methionine. cND = not determined. bRumen-protected

taining phenyl-β-D-glucopyranoside as an internal standard at 50 °C for 60 min (9); sample clean-up by passing through cation exchange resin (AG50W-8X; Bio-Rad, Richmond, CA) and then anion exchange resin (BIO-REX-5; Bio-Rad) (14); trimethylsilyl derivatization (22); and analysis by GLC (HP-5890; HewlettPackard, Wilmington, DE) using a crosslinked methyl-silicone capillary column (HP-1, 15 m × 0.32 mm × 0.1 µm film; Hewlett-Packard, Wilmington, DE) and flame ionization detector (10). Jugular blood was prepared for analysis and analyzed for amino acid concentration by cation exchange HPLC according to the procedures described by Campbell et al. (4). Statistical Analysis. During period 2, one steer refused to consume the supplemental cooked molasses block, so data for that steer collected during that period were removed from the analyses. Data were analyzed as Latin squares using the GLM procedure of SAS® (21). The statistical model contained the effects of animal, period, and treatment. Treatment means, determined using the LSMEANS option, were separated by using t tests for all possible comparisons among means when the overall F test for treatment was significant (P<0.05).

Results and Discussion Chemical compositions of forage and supplements are presented in Table 1. Whole shelled number 2 corn was used. The corn was analyzed to contain (dry basis) 0.01% Ca, 0.30% P, 0.10% Mg, 0.35% K, 0.01% Na, 2.3 ppm Cu, and 14.8 ppm Zn. The cooked molasses block was labeled to be not less than 30% CP, of which not more than 12% equivalent CP was provided by nonprotein N (urea). Predominant ingredients in the block included molasses products and by-products, animal fat, plant and animal proteins, and processed grain by-products. Total sugar content of the molasses block was 371 mg/g (dry basis) which included (milligrams per

58

Greenwood et al.

corn. These lower intakes illustrate the substitutive effect that lowTABLE 2. Effect of supplement strategy on OM, NDF, and N intakes protein high-energy supplements can and digestibilities in beef steers fed tallgrass-prairie hay. have on low-quality forage intake. Cochran (6) reported that when lowItem Control Corn Blocka RPMb SEM protein high-energy supplements were fed at levels higher than 0.5% of Forage intake, kg/d BW, intake of low-quality forages was OM 6.2d 5.5e 7.0c 5.9d 0.11 reduced by approximately 50% of the NDF 4.9d 4.3e 5.5c 4.7d 0.09 amount of supplement. Sanson and N 0.060d 0.053e 0.066c 0.057d 0.001 Clanton (20) reported that providing Total intake, kg/d steers supplemental corn at increasOM 6.2d 7.1c 7.3c 5.9d 0.11 ing percentages of BW decreased NDF 4.9d 4.6e 5.5c 4.7d,e 0.09 forage DM intake with the nadir at N 0.060e 0.075d 0.089c 0.057e 0.001 0.5% of BW, which yielded a substitutive ratio of 54%. In our investigaDigestible intake, kg/d tion, steers received supplemental OM 3.1d 3.6c 3.9c 2.9d 0.12 corn at approximately 0.5% of BW. NDF 2.4d 2.0e 2.9c 2.3d 0.08 Supplementation of 1.53 kg/d of corn N 0.016d 0.018d 0.036c 0.013d 0.002 OM decreased forage OM intake by Digestion,% 0.7 kg/d, yielding a substitution ratio OM 49.6 50.3 53.5 49.6 1.2 of 46%. NDF 49.2c 42.1d 52.9c 50.5c 1.4 Total OM intakes were increased N 25.7d 22.1d 40.2c 23.0d 2.9 (P<0.05) similarly by supplementation with either corn or cooked aCooked molasses block. molasses block. Intake of corn OM bRumen-protected methionine. provided 21% of the total OM intake, c,d,eMeans within rows with no common superscript differ significantly whereas OM provided by the cooked (P<0.05). molasses block represented only 4% of the total OM intake. This difference compensated for the lower intake of forage OM by steers fed corn than those fed the cooked ineffective in stimulating forage gram) fructose, 4.0; glucose, 4.3; molasses block. intake or digestion of prairie hay by sucrose, 351.4; and raffinose, 11.0. Responses for digestible OM intake beef steers. Steers fed the cooked By analysis, the molasses block were similar to those for total OM molasses block consumed more contained (dry basis) 2.8% Ca, 2.1% intake, because no significant differ(P<0.05) forage OM than those P, 0.34% Mg, 4.0% K, 1.1% Na, 10.4 ences in OM digestibility occurred assigned to other treatments. The ppm Cu, and 659 ppm Zn. Differamong treatments. However, total beneficial effect of providing molasences among treatments in mineral digestible OM intakes tended supply cannot be excluded as a factor ses blocks to ruminants fed low(P<0.06) to be higher for steers quality forage has been reported (2, influencing animal response. assigned to the cooked molasses Most steers readily consumed their 8, 12). Badurdeen et al. (2) reported block (3.9 kg/d) than for those fed a 10% increase in low-quality forage supplements each morning. Excepcorn (3.6 kg/d) even though more intake when bull calves were offered tions were one steer that completely a 56% CP molasses lickblock, whereas supplemental energy was provided by refused to consume the cooked the corn than the cooked molasses Hossain et al. (8) reported an 11% molasses block (removed from block. increase when sheep were offered a analysis) and one steer that did not Badurdeen et al. (2) reported that completely consume all of its supple- similar product. Kunju (12) reported DM digestibility and digestible DM a 29.5% increase in low-quality mental corn (retained for analysis). Reluctance of ruminants to consume forage intakes when Jersey bull calves intakes were not affected by lickblock supplementation, even though intake were supplemented with a urea molasses blocks is not uncommon of low-quality forage increased. We molasses block. We observed that and has been reported previously observed a 26% increase (P<0.05) in forage OM intake increased (P<0.05) (13). digestible OM intake compared to Intake and Digestion. The effects by 13% relative to control when the control, when steers were provided of supplement strategy on OM, NDF, cooked molasses block was fed. the cooked molasses block. Factors Forage OM intakes were lowest and N intakes and digestibilities are contributing to this increase were a (P<0.05) for steers fed supplemental reported in Table 2. The RPM was

Supplementation of Prairie Hay

59

cooked molasses block to have higher digestible OM intakes than those assigned to supplemental corn. They reported that across all levels of Amino acid Control Corn Blocka RPMb SEM protein supplementation (0.03% of BW to 0.12% of BW), starch supplementation depressed total digestible (µM) OM intake. In our experiment, even Taurine 24.4d 20.4e 19.8e 31.5c 1.1 though the supplemental corn and Aspartate 10.6 11.1 7.7 10.5 1.0 cooked molasses block treatments Threonine 61.7 51.3 55.2 58.3 4.5 Serine 60.0 59.5 48.8 53.3 4.1 provided the same amount of suppleAsparagine 24.9 24.2 19.6 25.1 1.8 mental CP, the additional starch Glutamine 64.8 66.3 65.4 65.3 2.4 provided by the corn probably was Glutamate 238.9 234.8 247.3 241.4 9.0 responsible for the depressed forage Glycine 171.2 159.6 169.7 160.3 8.7 digestion. Furthermore, this indiAlanine 182.2 197.9 191.6 206.5 8.7 cates that energy source and(or) Citrulline 61.7 58.4 45.8 57.1 6.6 amount can affect digestible OM Valine 273.6c 235.2d 263.1c 267.3c 8.9 intake; energy intake from the 21.5e 23.5d,e 35.9c 1.7 Methionine 26.2d supplement often is a poor indicator Isoleucine 119.9 105.2 114.8 115.4 4.2 Leucine 144.9 139.1 138.2 138.6 4.5 of energy available to the host. Tyrosine 48.9 44.0 43.5 46.2 1.7 The effects of supplement strategy Phenylalanine 57.8 53.8 52.1 56.0 1.5 on forage NDF intakes were consisTryptophan 37.2 33.3 32.9 36.1 1.7 tent with those on forage OM inOrnithine 67.0 72.3 66.5 81.7 10.8 takes. Total NDF intakes were highc d d c Lysine 127.2 98.6 98.7 131.1 7.0 est (P<0.05) for steers assigned to the c,d d d c Histidine 64.8 63.7 58.8 69.9 2.1 cooked molasses block treatment. Arginine 82.7c 70.2d 68.3d 86.1c 3.9 Steers assigned to the supplemental Total 1,951 1,820 1,831 1,974 52.5 corn treatment consumed less (P<0.05) total NDF than those aCooked molasses block. assigned to the control treatment. bRumen-protected methionine. Digestible NDF intakes were highest c,d,eMeans within rows with no common superscript differ significantly (P<0.05). (P<0.05) for steers assigned to the cooked molasses block treatment, whereas digestible NDF intakes were lowest (P<0.05) for steers assigned to They further reported that apparent 13% increase in forage OM intake, DM digestibility increased linearly as the supplemental corn treatment. 0.31 kg/d OM provided by the This decrease occurred because the supplemental corn intake increased, molasses block, and an 8% increase but, by assuming that the DM digest- digestibility of NDF was depressed in OM digestibility. Research results (P<0.05) 14% by supplemental corn reported by Okine and Mathison (18) ibility of corn was 90%, they calculated that DM digestibility of hay was when compared with control. illustrate the negative effect that Reported effects of corn suppleincreases in OM intake often have on not affected by corn supplementamentation on NDF digestion vary. tion. Applying the assumption that OM digestibility. We observed increases in both OM intake and OM OM digestibility of corn is 90% to our Sanson and Clanton (20) observed that providing supplemental corn up data, corn supplementation dedigestibility. Thus, when ruminally to 0.75% of BW did not negatively creased digestible OM intake proavailable N was supplied, digestion affect NDF digestion, whereas Chase vided by forage from 3.1 kg/d for rate must have increased more than control steers to 2.2 kg/d. Forage OM and Hibberd (5) and Matejovsky and enough to compensate for the Sanson (15) reported that providing digestion also was predicted to increased passage rate that would be supplemental corn at 0.5% of BW decline from 50% for the control expected with the higher intakes. steers to 39% when corn was supple- decreased NDF digestion. Chase and The increase in digestible OM Hibberd (5) noted NDF digestibilities mented. The depression in NDF intake for steers fed supplemental of 39.6% for control animals, corn agrees with the results of Sanson digestion (from 49 to 42%; Table 2) whereas animals receiving supplewhen corn was supplemented supand Clanton (20). They reported mental corn at 0.5% of BW had NDF ports this conclusion. that as supplemental corn intake digestibilities of 29.9%. Data of Olson et al. (19) could be increased, total digestible DM intake Forage N intakes, total N intakes, used to explain the tendency increased linearly, but digestible DM and digestible N intakes were highest (P<0.06) for steers assigned to the intake from hay decreased linearly.

TABLE 3. Effect of supplement strategy on plasma amino acid concentrations in beef steers.

60

(P<0.05) for steers assigned to the cooked molasses block treatment. Digestible N intakes were similar between steers assigned to the control and supplemental corn, even though total N intakes were higher (P<0.05) for steers supplemented with corn. Apparent N digestibility was greatest (P<0.05) for steers fed the cooked molasses block. With higher N intakes (as for the block treatment), apparent N digestion will increase, even if true digestibility is not affected, because of dilution of endogenous fecal N. The inability of increased N intakes to increase apparent N digestion for cornsupplemented steers is likely a response to a greater amount of fermentable substrate reaching the large intestine, which could increase microbial N contribution to the feces. We observed whole and fragmented corn in the feces of steers fed the corn treatment, which seems to support this explanation. Plasma Amino Acid Concentrations. The RPM increased (P<0.05) plasma methionine and taurine concentrations, indicating that it was effective in supplying absorbable methionine to the steers (Table 3), but it was nonetheless ineffective in stimulating forage intake or digestion of prairie hay by beef steers. Mercer et al. (17) suggested that methionine concentration could influence histidine catabolism and thus feed intake. Histidine degradation requires free tetrahydrofolate generated during the remethylation of homocysteine to methionine. In our study, plasma histidine concentrations were not decreased by RPM supplementation and were actually numerically higher. The inability of supplemental methionine to decrease plasma histidine concentrations was unexpected but leads us to assume that methionine availability did not limit histidine catabolism. Mercer et al. (16) also reported that elevated plasma histidine concentrations were associated with decreased feed intake. Steers fed the cooked molasses block had the highest forage OM intakes and also

Greenwood et al.

the lowest plasma histidine concentrations. However, when plasma histidine concentrations were expressed as a percentage of total plasma amino acid concentration, no differences were observed. Plasma lysine concentrations were lower (P<0.05) for steers fed the cooked molasses block and supplemental corn treatments, and plasma valine concentrations were lower for steers assigned to the supplemental corn treatment. The decrease in plasma lysine concentrations as digestible OM intake increased could be a result of increased deposition (or decreased mobilization) of body proteins as additional energy was available to the steers. The lower plasma valine concentrations for steers supplemented with corn could have been due to increased branchchain amino acid catabolism in response to increased supply of leucine from the corn (3). In conclusion, total available energy (digestible OM intake) for steers fed low-quality forage can be increased by supplementation with a cooked molasses block or corn. However, supplemental corn decreased forage intake and digestion. A limited supply of methionine does not appear to be an important factor regulating the intake of low-quality forage.

Amino Acids. Vol. 1. M. Friedman (Ed.). p 229. CRC Press, Boca Raton, FL. 4. Campbell, C. G., E. C. Titgemeyer, and G. St-Jean. 1997. Sulfur amino acid utilization by growing steers. J. Anim. Sci. 75:230. 5. Chase, C. C., and C. A. Hibberd. 1987. Utilization of low-quality native grass hay by beef cows fed increasing quantities of corn grain. J. Anim. Sci. 65:557. 6. Cochran, R. C. 1995. Developing optimal supplementation programs for range livestock. In Kansas State University Range Field Day 1995, 50 Years of Range Research Revisited. p 58. Cooperative Extension Service, Kansas State Univ., Manhattan, KS. 7. DelCurto, T., R. C. Cochran, L. R. Corah, A. A. Beharka, E. S. Vanzant, and D. E. Johnson. 1990. Supplementation of dormant tallgrassprairie forage: II. Performance and forage utilization characteristics in grazing beef cattle receiving supplements of different protein concentrations. J. Anim. Sci. 68:532. 8. Hossain, K. B., N. R. Sarker, M. Saadullah, M.A.H. Beg, and T. M. Khan. 1995. Effect of feeding straw supplementing with urea molasses block lick on the performance of sheep. Asian-Australasian J. Anim. Sci. 8:289. 9. Johansen, H. N., V. Gilitsø, and K.E.B. Kundsen. 1996. Influence of extraction solvent and temperature on the quantitative determination of oligosaccharides from plant materials by high-performance liquid chromatography. J. Agric. Food Chem. 44:1470. 10. Juvik, J. A., and D. R. LaBonte. 1988. Single-kernel analysis for the presence of the sugary enhancer (se) gene in sweet corn. Hort. Sci. 23:384. 11. Köster, H. H., R. C. Cochran, E. C. Titgemeyer, E. S. Vanzant, I. Abdelgadir, and G. St-Jean. 1996. Effect of increasing degradable intake protein on intake and digestion of low-quality, tallgrass-prairie forage by beef cows. J. Anim. Sci. 74:2473. 12. Kunju, P.J.G. 1988. Development of urea molasses block and its field application in India (a review). Asian-Australasian J. Anim. Sci. 1:233.

Literature Cited 1. AOAC. 1994. Official Methods of Analysis. (16th Ed.). Association of Official Analytical Chemists, Arlington, VA. 2. Badurdeen, A. L., M.N.M. Ibrahim, and S.S.E. Ranawana. 1994. Methods to improve utilization of rice straw. III. Effect of urea ammonia treatment and urea molasses blocks supplementation on intake, digestibility, rumen and blood parameters. AsianAustralasian J. Anim. Sci. 7:363. 3. Block, K. P. 1989. Interactions among leucine, isoleucine, and valine with special reference to the branched-chain amino acid antagonism. In Absorption and Utilization of

13. Lobato, J.F.P., G. R. Pearce, and D. E. Tribe. 1980. Measurement of the variability in intake by sheep of oat grain, hay and molasses-urea blocks using chromic oxide as a marker. Aust. J. Exp. Agric. Anim. Husb. 20:413. 14. Low, N. H., A. Brause, and E. Wilhelmsen. 1994. Normative data for commercial pineapple juice from concentrate. J. AOAC Int. 77:965. 15. Matejovsky, K. M., and D. W. Sanson. 1995. Intake and digestion of low-, medium-, and high-quality grass hays by lambs receiving increasing levels of corn supplementation. J. Anim. Sci. 73:2156. 16. Mercer, L. P., S. J. Dodds, M. R. Schweisthal, and J. D. Dunn. 1989. Brain histidine and food intake in rats fed diets deficient in single amino acids. J. Nutr. 119:66.

61

Supplementation of Prairie Hay

17. Mercer, L. P., C. D. Gifford, and S. J. Dodds. 1989. Histidine-methionine metabolic interrelationships. In Absorption and Utilization of Amino Acids. Vol. 1. M. Friedman (Ed.). p 189. CRC Press, Boca Raton, FL. 18. Okine, E. K., and G. W. Mathison. 1991. Effects of feed intake on particle distribution, passage rate, and extent of digestion in the gastrointestinal tract of cattle. J. Anim. Sci. 69:3435.

19. Olson, K. C., R. C. Cochran, T. J. Jones, E. S. Vanzant, and E. C. Titgemeyer. 1997. Effects of various supplemental starch and protein levels on ruminal fermentation and liquid passage of beef steers fed tallgrass-prairie hay. In Cattlemen’s Day 1997, Report of Progress 783. p 52. Agric. Exp. Sta., Kansas State Univ., Manhattan, KS. 20. Sanson, D. W., and D. C. Clanton. 1989. Intake and digestibility of low-quality meadow hay by cattle receiving various levels of whole shelled corn. J. Anim. Sci. 67:2854.

21. SAS. 1988. SAS/STAT® User’s Guide (Release 6.03). SAS Inst. Inc., Cary, NC. 22. Sweeley, C. C., R. Bentley, M. Makita, and W. W. Wells. 1963. Gas-liquid chromatography of trimethylsilyl derivatives of sugars and related substances. J. Am. Chem. Soc. 85:2497. 23. Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583.