Intake, Digestibility, and In Situ Digestion Kinetics of Treated Wheat Straw and Alfalfa Mixtures Fed to Holstein Heifers

Intake, Digestibility, and In Situ Digestion Kinetics of Treated Wheat Straw and Alfalfa Mixtures Fed to Holstein Heifers D. G. ATWELL,' N. R. MERCHEN, E. H. JASTER, G. c. FAHEY, JR., L. L. BERGER, E. C. TITGEMEYER, and L. D. BOURQUIN Department of Animal Sdences University of Illinois Urbana 61801 ABSTRACT

Twelve Holstein heifers averaging 370 kg of BW (4 animals fitted with permanent ruminal cannulas and 8 intact animals) were used in three replications of a 4 x 4 Latin square design to determine effects of feeding combinations of alkaline hydrogen peroxide-treated wheat straw and alfalfa haylage on ad libitum nutrient intake and digestibility and Nmind characteristics. A second experiment was conducted simultaneously to determine effects of feeding combinations of these forages on in situ digestion kinetics of both treated wheat straw and alfalfa. Diets consisted of an 80:20 forage to concentrate ratio (DM basis), and dietary designations were based on DM ratios of treated wheat straw:alfalfa haylage. Positive associative effects were noted for both DM and OM intakes due to addition of alfalfa; greatest increases occurred when the lowest (27%) level of alfalfa was added. Dry matter and OM intakes increased by 12 and 14%, respectively, when diet 53:27 was compared with diet 800. Digestibility of OM was similar across diets, averaging 63.6%. Associative effects were not noted for total tract fiber digestibilities. Positive associative effects of combinations of the forages were noted for in situ rates of disappearance of DM, NDF, and certain hemicellulose neutral monosaccharides (arabinose, galactose, mannose, and xylose) of both treated wheat straw and alfalfa haylage. Apparent discrepancies

Received December 6, 1990. Accepted May 20, 1991. 'current address: rowm mark, Bloomington. tL 61702. 1991 J Dairy Sci 743524-3534

IUC.,

PO

BOX

between in vivo and in situ data may have been due to compensatory hindgut fermentation masking improvements in ruminal digestibility when combinations of the forages were fed. (Key words: treated wheat straw, alfalfa, neutral monosaccharides)

Abbreviation key: AHP = alkaline hydrogen peroxide, DIP = degradable intake protein, DMD = DM digestibility, DR = dilution rate, HNM = hemicellulose neutral monosaccharides, LDR = liquid dilution rate, OMD = OM digestibility, OM1 = OM intake, PDR = particulate dilution rate, WS = wheat straw. INTRODUCTION

Chemical pretreatment has been the most significant technique used for improving the nutritional value of cereal straws for ruminants. In recent years, the alkaline hydrogen peroxide (AHP) treatment process developed by Gould (9) has shown particular promise in increasing the availability of structural carbohydrates of cereal straw to ruminal microorganisms (13). The process increases availability of structural carbohydrates by combining both alkaline hydrolysis and peroxide oxidation to reduce the integrity of the lignin-hemicellulose matrix of the plant cell Wall.

The ability of the A€P process to increase intake and digestibility of wheat straw (WS) compared with untreated WS is well documented (14). However, evidence exists that further enhancements in intake and digestibility of AHP-WS may be obtained by adding relatively small amounts of a high quality forage such as alfalfa to diets containing AHPWS (4, 21, 26). ZOO, The mechanism by which alfalfa improves utilization of alkali-treated crop residues may 3524

3525

TREATED WHEAT STRAW-ALFALFA COMBINATIONS TABLE 1.

Ingredient and chemical composition of diets fed to dairy heifers.

Item

AHP-WS:Alfalfa haylage, 5% DM1 5327 2753

8O:O

080

Ingredient composition

AHP-ws Alfalfa baylage Urta Corn gluten mcal Ground corn Dicalcium phosphate Calcium sulfate Miacral and vitamin mix2 Chemical composition DM. OM

CP NDF

ADF DIP? 96 of CP

80 1 9.2 8.5

.72 .23 .35 65.7 86.2 12.9 53.5 36.8 66.8

53 27 1 1.6 165 55 .35 64.3 87.8 13.6 47.4 32.3 77.0

27 53 1

80 1

18.3 .35

18.3 .35

.35

.35

63.4 89.0 17.5 41.9 27.6 78.3

62.4 89.9 22.5 36.0 23.3 77.6

'AHP-WS = Aliraline hydrogen pcroxidatreatad wheat straw. *MiaemIs (mglkg diet DM): S, 350; K, 262; Mg, 175; Mn, 105; ZS 105; Fe, 7 4 Cu, 18; I, .88; Se, .5; Co, .12. Vitamins (IU/kg diet DM): A, 7709; D3, 2313; E. 27. b I P = Degradable intake protein. Values were estimated using data from NRC (19) and assuming AHP-WS protein to be 80% DIP.

reside in its complementary nature. Treated crop residues such as AHP-WS are primarily energy sources because they generally are low in Ca, P, trace minerals, nonstructural carbohydrates, and ~ m i n a l l ydegradable intake protein (DIP). Alfalfa, however, is a relatively good source of these nutrients. Paterson et al. (21) suggested that alfalfa may improve digestibility by slowing the rate of digesta passage from the rumen of animals consuming high amounts of alkali-treated crop residues. Additionally, alfalfa generally is well accepted by ruminants. Given these factors, it is possible that feeding these two forages together may improve the utilization of AHP-WS. Dairy heifers typically are fed high forage diets; consequently, they represent a good target species for the feeding of AHP-WS:alfalfa combinations. Experiment 1 was conducted to study the effects of feeding combinations of AHP-WS and alfalfa haylage on ad libitum nutrient intake, total @act digestibilities @My OM, CP, NDF. ADF, and cell content), and ruminal characteristics of Holstein heifers. Experiment 2 was conducted to determine the effect of diets in Experiment 1 on in situ lag

time and rate and extent of DM, NDF, and hemicellulose neutral monosaccharides (HNM) disappearance of both AHP-WS and alfalfa haylage. MATERIALS AND METHODS

Experiment 1

Animals and Diets. Twelve Holstein heifers weighing an average of 370 kg (4 animals fitted with permanent ruminal cannulas and 8 intact animals) were used in three replications of a 4 x 4 Latin square design. Diets ("able 1) consisted of an 8020 forage:concentrate ratio on a DM basis. Dietary designations were based on DM ratios of AHP-WS:alfalfa haylage in the diet: 800, 53:27, 2753, and 0:80. Native WS was treated as described by k a v a et aL (5); however, larger batches of approximately 115 kg of W S were processed for this experiment. Additionally, AH?'-WS was s t o d in an upright oxygen-limiting silo until it was fed. Treated WS contained 62% DM; OM, CP, NDF, and ADF averaged 85, 2.8, 64.5, and 45.3% of DM, respectively. Alfalfa was harJonmal of Dairy Science Vol. 74. No. 10, 1991

3526

ATWELL ET AL.

vested in the early bloom stage, chopped to a length of approximately 5 cm,and stored in an oxygen-limiting silo prior to feeding. Alfalfa haylage contained 58.8% DM, OM, CP, NDF, and ADF averaged 88.6,22.2,42.5, and 28.1% of DM, respectively. Diets were b a l a n d to meet or exceed NRC (19) requirements for CP, Ca, P, K, trace minerals, and vitamins A, D, and E for growing dairy heifers greater than 12 mo of age. Concentrates for diets 80:O and 53: 27 contained corn gluten meal as the major source of hue protein in an effort to limit supply of DIP. Diet 80:O had the lowest estimated DIP value at 66.8%of CP.Over 30% of this value was contributed by urea 0. The presence of urea and alfalfa in the remaining diets had the combined effect that DIP was relatively high, averaging 77.6% of CP across these diets. Urea was added to diets 800 and 53:27 to meet requirements for CP.In order to avoid a confounding effect of urea on intake, urea was added at the same level to diets 2753 and 0:80.Concentrate and forage portions of the diet were weighed and mechanically mixed daily for each animal and offered in equal portions at 0800 and 2000 h at a level to ensure 10%feed refusal. Heifers were housed in stanchions with individual mangers and water cups. Animals were allowed to exercise in a drylot adjoiniig the barn from O900 to 1100 h daily, weather and sampling schedule permitting. Sampling Procedures. Experimental periods were 21 d in length with a 14-d adaptation phase followed by a 7 d collection phase. Feed offered and refused was monitored daily throughout each period, and DMI was C ~ C U lafed as the mean intake from d 12 through 21. Samples of forages and concentrates were taken daily on d 14 through 21. Feed refusals were analyzed and used to correct for differences between composition of feed offered and that consumed. Heifers received boluses of 7.5 g of CrzO3 twice daily at 12-h intervals during d 8 through 21 of each period. Fecal grab samples were collected twice daily on d 15 though 20 in a sampling scheme such that a sample was taken at each 1-h interval between the morning and evening feedings. A 100-g aliquot of each sample was composited by animal and period, dried at 55'C, and ground (2-mm screen) prior to analysis. Strained ruminal fluid (30 ml) was taken from cannulated animals at 2-h intervals beJomnal of Dairy Science VoL 74. No. 10, 1991

tween the morning and evening feeding on d 17, analyzed for pH, and acidified with 1.2 ml 6N HCl. On d 17 of each period, the moming

feeding for cannulated heifers was marked with 1 g of Yb, and these heifers were given an intraNmul * al dose of 2 g of Co as Co-EDTA (27). Whole ruminal contents were taken from several sites within the m e n to obtain representative samples of 300 to 400 g at 4, 8, 12, 18,24, 36, and 48 h following marker administration to determine particulate (Yb) and liquid (Co) dilution rates from the rumen. Whole ruminal contents were partitioned into particulate and fluid fractions by squeezing through eight layers of cheesecloth. Ruminal fluid samples were mtrifuged (18,000 x g for 20 min), and Co was determined in the supernatant. Particulate matter was dried at 55'C and ground (2-mm screen) before Yb analysis. Sample Analyses. Feed, feed refused, and fecal samples were analyzed for DM, OM, and Kjeldahl N (2). NDF (23). and ADF (8). Fecal samples were analyzed for Cr (29), and fecal DM excretion was calculated by dividing Cr intake by the Cr concentration in feces. Fecal output of various nutrients was determined by multiplying concentration of a nutrient in feces by daily fecal output of DM. Ytterbium was extracted from ruminal particulate samples as described by Hart and Polan (12) and quantitated as described by Merchen et al. (16). Ruminal fluid samples were analyzed for Co as described by Merchen et al. (16). Particulate and liquid dilution rates were determined as the slope of the regression of the natural logarithm of Yb and Co concentrations, respectively, on time. Ruminal fluid samples were analyzed for NH3 N (6) and VFA (16). Staristical Analyses. Data were analyzed using the general linear models procedure of SAS (24). Intake and total tract digestibility data were analyzed using data from the three 4 x 4 Latin squares with 2 df for squares, 9 for animal, 9 for period, 3 for diet, and 24 for error. Sums of squares for diet were further partitioned into orthogonal contrasts as follows: 1) linear, 2) quadratic, and 3) cubic effects of dietary M - W S or alfalfa Ruminal data collected from cannulated heifers were analyzed as a 4 x 4 Latin square. The model included animal, period, and diet effects. Sums of squares for diet were separated further into orthogonal contrasts as described earlier. Data collected at different times postfeeding (VFA,

3527

TREATED WHEAT STRAW-ALFALFA COMBINATIONS

N H 3 N, and pH) were analyzed as described for each time interval. Differences due to diet were consistent at each point of time; therefore, data for these variables were summarized, and analyses of mean values over all time intervals were conducted as described. Significance was declared at P < -05 unless otherwise noted.

substrate for each animal in each period were introduced into the rumen simultaneously at the morning feeding on d 17, and duplicate samples of each substrate were removed at the time periads indicated. On removal from the rumen, all bags were rinsed and hand squeezed under cold tap water until rinse water was clear. zero-hour bags were soaked in tap water for 1 h prior to being rinsed as mentioned. Bags subsequently were dried at 55'C for 48 h Experlrnent 2 prior to analyses. Substrates and Procedures. The four rumiSubstrate Analyses. Dried contents were naUy cannulated Holstein heifers from Experi- emptied from bags, and duplicates were comment 1 were used simultaneously as experi- posited. The NDF (8) content then was determental animals in this trial. The experimental mined using two subsamples of the composited design was a 4 x 4 Latin square. Substrates for material, and the resultant NDF-extracted resiExperiment 2 were AHP-WS and alfalfa hay- due was composited. Extracted residues from lage. The concentrations of nutrients in &&'- bags incubated for 0, 6, 12, 18, 24, 30, and 48 W S and alfalfa haylage were similar to those h as well as NDF extracts of the original reported in Experiment 1. Both substrates were substrates then were ground in a Wig-L-Bug dried (5s'c) in a forced-air oven and ground to (Crescent Dental Co., Lyons, la) to prepare a pass a 4-mm screen.Duplicate, 4-g (DM) sam- highly uniform sample for determination of ples of AHF'-WS and alfalfa haylage were HNM content. The HNM were prepared and weighed into 7- x 1 k m dacron bags (20- to analyzed using hydrolytic method 2 reported 70-pm pore size) and suspended in the rumen by Garleb et al. (7), with the exception that the of each heifex in each period for 6, 12, 18,24, inositol (internal standard) concentration of 30, 36, 48, and 72 h. Sixteen bags of each 72% H2SO4 was 300 mg/dl.

TABLE 2. Effects of feeding different combinationsof AHP-WS' and alfnlfn hayla@ on nutrient intake and digestibility by dairy heifers. 8&0

Item Intake DM. Wd' DM, 46 BW'

8.3 2.26 7.0 1.1 4.3 3.0 2.7

OM. Wd. CP, kgld' NDP, Wda ADP, kg/da CC, kgld2*b Digestibility, 96 DM~ OM Cpc N D P

65 4 64.5 60.4 68.3 68.1 58.2

ADP ccb ~~

AHP-WS:AlfaLfa haylage 46 DM 53:27 2753

9.3 2.54 8.0 1.3 4.4 3.0 3.6 64.4 63.6 55.8 62.3 61.4 65.0

9.8 2.67 8.5 1.7 4.0 2.7 45 63.0 63.3 60.4 545 512 71.0

0:80

9.8 2.67 8.6 2.2 3.4 22 52 61.5 63.1 63.7 43.1 37.1 76.1

SE .2

-04 .2 <.1 <.l <1 .1 .5

.6 9 .8 1.o 1.o

~

.m).

'Qmdratic effect of diet (P < bLinear d e c t of diet (P e .OS). 'Cubic effect of did (P < .05).

'AHP-WS = Alkaline hydmgcn pxidetreated what straw.

2ce = cell

contents

= OM-NDF.

I o d of Dairy Science Vol. 74, No. 10, 1991

Item

8o:O

Toml VPA, mM Acetate,’ mol/lOO mol Ropionate, mol/lOO mol Isobntyrate? mol/lOO mol Butyrate? moUlOO mol Isovalmte,b movloo mol Valerate,” moVlOO mol Ruminal pH N H 3 N, mg/lOO dl’ Liquid dilution rate (Co). %/b Particulate dilution rate (Yb)),%/b Ruminal volume, L

122.4 75.1 17.1 .43 6.7 .31 .43 7.01 4.4 7.6 3.7 81.7

A€W-WS:Alfalfa haylage, % DM 5327 2753 117.4 74.2 16.2 .67 7.8 .39 .80 7.04 8.9 7.4 4.7 83.7

114.9 72.0 16.2 .a4 8.7 .93 1.21 6.74 15.4 7.6 4.4 79.2

0230

SE

114.9 70.7 16.1 1.10 9.0 1.40 1.65 6.66 23.7 7.6 4.8 68.4

3.2 .6 .4 .08

.3

.w

.o 1 .30 1.6 .3 .6 5.1

%inear effect due to diet (P < ,OS). bCubic effect due to diet (P < .05). lAHP-WS = Alkaline hydrogen peroxide-treated wheat straw.

Statistical Analyses. Estimates for lag time and rate and extent of DM, NDF, and HNM disappearance were obtained using the brokenline model reported by Mertens and Loften (17) in conjunction with Marquardt’s iterative method of the nonlinear models procedure of SAS (24). Rates calculated using this model may be interpreted as percentage per hour disappearance of the potentially digestible fraction. The potentially digestible fraction was defined as 1 - [fraction initially solubilized (0 h bag) + indigestible fraction]. Extents calculated using this model may be interpreted as 1 - indigestible fraction. Extents were estimated assuming infinite ruminal incubation time. Parameter estimates then were analyzed using the general linear models p d u r e of SAS (24). The model used for data analysis was identical to that described for ruminal data in Experiment 1. Significance was declared at P e .05 unless otherwise noted. RESULTS

Experlrnent 1

There was a quadratic effect due to diet for DMI expressed as either weight per day or percentage of BW (Table 2). Intake increased above that seen on the high AHP-WSdiet (80: 0) by 12% when alfalfa was substituted for AIW-WS at the 27% level. Intake increased another .5 kg/d (5%) when alfalfa comprised Journal of Daky Science Vol. 74, No. 10, 1991

57 or 80% of diet DM. Intake of OM also increased in a significant quadratic manner with increasing level of alfalfa. The largest difference between diets in OM intake (OMI; 1 kg/& 14%) also occurred when 27% alfalfa was substituted for AHP-WS. Intake of CP increased quadratically with increasing level of alfalfa. Neutral detergent fiber and ADF intakes both increased quadratically with increasing level of dietary AHP-WS. Intake of cell content (OM-NDF) increased linearly with increasing level of alfalfa, Apparent DM digestibility (DMD) decreased linearly from 65.4% for diet 80:O to 61.5% for diet 0:80 as the level of dietary alfaLfa increased. However, OM digestibility (OMD) was unaffected by diet, averaging 63.6% across diets. Crude protein digestibility responded in a cubic manner to diet, demonstrating no consistent pattern in response to changing levels of AHP-WS of alfalfa The apparent digestibility of both NDF and ADF increased quadratically with increasing level of AHP-WS. Digestibility of NDF and ADF increased from 43.1 and 37.1%. respectively, on diet 0:80 to 68.3 and 68.1%, respectively, on diet 80:O. Total concentration of VFA was not affected by diet, averaging 117 mM (Table 3). Molar proportion of acetate decreased, whereas molar proportions of all other VFA except propionate increased with increasing level of alfalfa. Molar proportion of propionate was

3529

TRFATED WHEAT STRAW-ALFALF'A COMBINATIONS

TABLE 4. Effect of feeding different combinations of AHP-WS' and alfalfa haylage on in situ lag time and rate2 and exten? of DM, NLW, and hemicellulose nentral monosaccharide (?INMl disappearance of AHP-WS. ItUU

80:O

5327

2753

0:80

SE

3.4 3.3 99.1

4.1 4.7 95.3

5.2 5.4

1.o

93.4

4.3 3.9 95.7

3.2 3.4 99 .O

2.8 4.8 94.2

3.7 5 .O 92.1

3 .O 4.0 94.4

.8 .3 1.7

ND4 8.2 86.9

.6 10.3 87.7

.6 9.4 90.9

.3 7.9 90.4

.3 .9 1.5

6.4 4.2 93 5

4.3 5.4 97.1

5.3 6.3 96.5

4.1 4.0 98.8

3.2 1.2 34

.18 5.9 89.1

.82 6.7 91.3

.53 6.1 95 .J

5.2 94.9

DM Lag, h Rate, %/ha &tent 96'

.4

.9

NDF Lag. h Rate, %/ha Extent % HNM Arabinose Lag. h Rate, %/h Extern % Galactose

Lag, h Rate, %/h Extent, % Xylose Lag. h Rate. %/ll

Extent

96

.a

.2 .6 3.4

effect due to diet (P < .05). lAHp-WS = Au;aline hydrogen peroxidetreated wheat straw. 'Rate is defined as percentage per hour disappearaoce of potmtia~ydigestiite DIM, NDF, and HNM. %tent is defmed as 1 - percentage indigestible DM, NDF, and HNM. %ot detectable. -tic

unaffected by diet, averaging 16.4. Ruminal ever, its concentration was so low (1.5 mg/g of pH also was unaffected by diet, averaging NDF) in the unincubated substrate that analy6.86. Ruminal N H 3 N increased linearly with sis of rhamnose in incubated samples was not increasing alfalfa from 4.4 mg/d on diet 800 justified. Table 4 presents the effects of feeding difto 23.7 mg/dl for diet 0:80. Ruminal liquid dilution rate (LDR) and particulate dilution ferent combinations of AHP-WS and alfalfa on rate (PDR) were unaffected by diet, averaging in situ lag time and rate and extent of DM, 7.6 and 4.496/h, respectively. Ruminal volume NDF, and HNM disappearance of AHP-WS. Lag times were unaffected by diet, averaging was unaffected by diet, averaging 78 L. 4.2, 3.2, .4, 5, and .J h for DM, NDF, arabinose, galactose, and xylose, respectively. Experiment 2 Rates of both DM and NDP disappearance The NDF-extracted residue of unincubated responded in a quadratic manner to diet. Rates AHP-WS contained 37, 4, and 307 mg of of DM and NDF disappearance were greater arabinose, galactose, and xylose, respectively, for AHP-WS incubations when animals were per gram of NDF. Mannose was not detectable fed diets containing combinations of the two in AHP-WS. The NDF-extracted residue of forages (53:27 and 2753) than when fed either unincubated alfalfa haylage contained 20, 16, forage alone. Rates of DM disappearance for 16, and 138 mg of arabinose, galactose, man- diets 53:27 and 27:53 were 4.7 and 5.4%/h, nose, and xylose, respectively, per gram of respectively, whereas rates of DM disappearNDF. Rhamnose was detected in a l f a l f ~how- ance for diets 80:O and 0:80 were 3.3 and Journal of Dairy Science Vol. 74, No. 10, 1991

3530

ATWELL ET AL.

TABLE 5. Effects of feeding different combinations of AHP-WSl and alfalfa haylage on in situ lag lime and rate2 and extent? of DM, NDF, and heanicelldose mutd monosaccharide (HN?vl) dirappearance of alfalfa haylage. AHP-WSMalfa haylane. % DM Item

8030

53:27

2753

080

SE

3.2 8.6 81.0

1.8 14.6 79.5

2.7 15.5 79.2

1.4 11.6 795

.7 1.4 A

3.0 7.7 58.0

1.9 11.6 56.0

2.4 12.0 55.4

1.3 9.6 55.5

.9 1.3 1

1.8 15.4 84.7

15 26.0

84.7

1.3 20.6 85.4

.8 23.7 85.4

.6 2.7 .8

2.7 9.3 86.6

2.2 22.3 83.6

3.4 22.4 83.1

.8 12.3 85.7

9 3 .O 1.1

7.9 9.8 80.6

8.6 18.9 77.9

62 20.8 76.1

5.6 12.6 77.7

2.7 7.8 3.3

.2 7.2 44.8

ND4

2.0 20.8 38.7

.6 7.6 44.6

.7 1.8 2.1

DM Lag, h Rate, %/ha Extent, % NDF Lag. h Rate, %/ha Extent, % Arabinose Lag, h Rate, %/h ExtenL % Galactose Lag, h Rate, %ha Extent, %"

.o

UannOSC

Lag, h Rate, %/h Extent, % Xylose Lag. h Rate, %pb Extent, 96'

11.0 38.3

BQuadraticeffect due to diet (P < ,06). bCubic effect due to diet (P < .05).

'AHP-WS = Alkaline hydrogen peroxide-treated wheat straw. 2Rate is ddioed as percentage per hour disappearance of potentially digestible DM, NDF, and HNM. 'Extent is defincd as 1 - percentage indigestible DM, NDF, and HNM. 4Not detectable.

3.9%/h, respectively. Rates of NDF disappearance for diets 53:27 and 2753 were 4.8 and 5%/h, respectively, compared with rates of NDF disappearance for diets 80:O and 0 8 0 of 3.4 and 4%h, respectively. No significant effects due to diet were noted for the rates of disappearance of the HNM. Extent of disap pearance of DM increased quadratically with increasing level of AHP-WS,from 95.7% for diet 0:80 to 99.1% for diet 800. Extents of disappearance of NDF, arabinose, galactose, and xylose were unaffected by diet, averaging 95, 89, 96, and 93%, respectively. Table 5 presents results describing effects of feeding different combinations of AHP-WS and alfalfa on in situ lag time and rate and extent of DM, NDF, and HNM disappearance Journal of Dairy Science VoL 74. No. 10, 1991

of alfalfa haylage. Lag times were unaffected by diet, averaging 2.3,2.2, 1.4.2.3.7.1, and .7 h for DM, NDF, arabinose, galactose, mannose, and xylose, respectively. Rates of &sap pearance of DM, NDF, and galactose remanner due to sponded in a quadratic (P< .M) diet. Rates of disappearance for all three variables were greater when combinations of the forages were fed than when forages were fed alone. Similarly, rate of xylose disappearance responded in a cubic manner to diet. Rates of xylose disappearance also were greater when combinations of the forages were fed than when forages were fed alone. Rates of arabinose and mannose disappearance were quite variable and were not significantly affected by diet. Extent of DM, NDF, arabinose,

TREATED WHEAT S'IRAW-ALPALPA COMBINATIONS

3531

and mannose disappearance was not affected gut. Apparent DMD increased linearly with by diet, averaging 80,56,85, and 78%, respec- increasing level of AHP-WS from 61.5% on tively. Extent of both alfalfa galactose and diet 080 to 65.4% on diet 80:O. However, this xylose disappearance responded quadratically may have been due to the high digestibility of to diet. Extent of disappearance of these two Na in the ash component of the treated WS. sugars was greater for diets 8O:O and 0 8 0 than Maeng et al. (15) observed that virtually all of for diets that contained combinations of the the Na ingested by sheep fed NaOH-treated two forages (53:27 and 2753). barley straw was excreted in the urine. The Na content of AHP-WS used in this study was approximately 3% of WS DM. Increased inDISCUSSION take may have been due to an improvement in diet acceptability with the addition of alfalfa. Experlrnent 1 Additionally, the high Na content of diet 80:O The quadratic increases in DMI (weight per may have reduced intake due to an effect on day and percentage BW) and OMI (Table 2) nuninal osmolarity (11). Intakes of CP, NDF, with increasing level of alfalfa indicate a mod- ADF, and cell content can be explained based est positive associative effect on intake when on their dietary concentrations. The apparent digestibility of NDF and ADF combinations of the two forages were fed. A linear increase would have indicated a re- increased quadraticaUy with increasing level of sponse to alfalfa alone. The greatest improve- AHP-WS and was due to the more digestible ment in DMI and OMI occurred when 27% nature of these fractions in the treated WS alfalfa was added Associative effects on in- compared with alfalfa. The fact that fibex ditake when relatively small amounts of alfalfa gestibility was not improved with the addition were added to diets containing treated crop of alfalfa may indicate that ruminal microorgresidues have been observed by others (21, anisms were not limited in their ability to 26). Paterson et al. (21) and Soofi et al. (26) degrade AHP-WS by availability of DIP or attributed the improvements in intake with ad- other nutrients contained in alfalfa. Corn gludition of alfalfa to improved ruminal digesti- ten meal, which contains a significant portion bility of fiber. However, in the present study, of ruminally undegradable protein (18), was although the apparent digestibility of both used as the major source of supplemental true NDF and ADF increased quadratically with protein in the concentrate portion of diets 800 increasing level of AHP-WS, the fiber digesti- and 53:27. By limiting DIP, as was done by bility observed for diets containing combina- Paterson et al. (21) and Brandt and Klopfentions of the forages (53:27 and 2753) were not stein (4), we expected the same pronounced different from that expected calculated from positive associative effects on digestibility. weighted means of forages in blends. Assum- Additionally, the degradability of alfalfa fiber ing that the digestibility of NDF and ADF did not appear to be enhanced by the presence remained the same for both forages, weighted of m - w s . Approximately 20 percentage units of the means for NDF and ADF digestibility would be 62 and 60.7%, respectively, for diet 53:27 material analyzing as NDF in WS is solubiand 54 and 51.1%, respectively, for diet 2753. lized by AHP. Untreated W S has an NDF These predictions for apparent digestibility of value of approximately 85% compared with NDF and A D F are quite similar to the 62.3 65% for AHP-WS.The digestibility of cell and 61.4% observed for diet 53:27 and the content in this study decreased linearly with 54.5 and 51.2% observed for diet 2753. Fur- increasing AJiIP-WS from 76.1 to 58.2%. re thermore, the fact that apparent OMJ3 was spectively, for diets 0:80 and 80:O. The similar among diets indicates that improve- reduced digestibility of a fraction that is norments in intake probably were not due to mally highly digestible (cell content) mitigates improved diet digestibility. It is possible that the improvements in fiber digestibility obruminal digestibility of fiber was enhanced served as a result of the treatment process. when combinations of the forages were fed, Reduced digestibility of AHP-WScell content but differences in ruminal digestibility were helps explain the similar OMD among diets masked by subsequent digestion in the hind- that demonstrated vastly different fiber digestiJournal of Dairy Scicnce Vol. 74, No. 10, 1991

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ATWELL

bilities. The lower intake and digestibility of cell content observed for animals fed the high AHP-WS diets would seem to argue for positive associative effects on ruminal and total tract nutrient digestibility of fiber when combinations of the forages were fed. Alfalfa would be a source of digestible cell content that would include nonstructural carbohydrates as an energy source for ruminal microbes. However, as previously observed, ruminal microbes were apparently not limited by nutrients contained in the cell content fraction of alfalfa The high molar propoaion of acetate (Table 3) in ruminal VFA is typical of high forage diets. Linear and cubic increases in the molar proportions of isobutyrate and isovalerate, respectively, with increasing level of alfalfa protein are indicative of its extensive ruminal degradation (20). Ruminal pH was relatively constant across diets, averaging 6.86. The linear increase in ruminal NH3 N with increasing level of alfalfa was predictable given the concentration of CP in the diet (Table 1) and the high ruminal degradability of alfalfa protein (18). Our failure to detect a difference because of diet in ruminal LDR and PDR is somewhat surprising. Berger et al. (3) indicated that Nmind dilution rate @R) was increased because of NaOH treatment of corn cobs. Therefore, it might be predicted that ruminal DR would be higher for heifers fed diets high in AHP-WS with its accompanying Na content. There are several possible explanations for the lack of difference in DR observed in the present study. Rumination time may have been greater when animals consumed higher amounts of alfalfa. The increased time spent ruminating would increase saliva flow to the rumen and, consequently, may have increased DR to that observed when heifers consumed large amounts of AHP-WS.The chemically treated substrate and method used to determine DR in the work of Berger et al. (3) were different from those of our study. It may not be reasonable to compare NaOH-treated corn cobs with AHPWS. Many factors such as particle size, specific gravity, and susceptibility to microbial digestion affect the rate at which digesta leaves the rumen (1, 22). Chemically treated corn cobs used by Berger et al. (3) were ground to pass a .65-cm screen, whereas AHP-WS used in our study was ground to pass a .95cm screen. Differences in initial particle size and Journal of Dairy Science Vol. 74, No. 10, 1991

ET AL.

physicochemical characteristics of the substrates may contribute to differences observed in DR. Additionally, Berger et al. (3) used CrzO3 as a digesta flow marker, whereas both Co-EDTA and Yb were used in our study. Chromic oxide is a nonspecific digesta flow marker, Co-EDTA is a fluid phase marker, and Yb is a particulate phase marker. Therefore, differences observed between DR in the two studies may be due partially to differences in marken used. Experiment 2

Rate of in situ disappearance of AHP-WS (Table 4) appeared to be the variable most affected by diet. Rates of both DM and MIF disappearance responded quadratically to diet and were greater for those containing combinations of the two forages (53:27and 2753)than for those containing either AHP-WS (800) or alfalfa (0:80) alone. Although rates of disappearance of HNM were not significantly affected by diet, observed values were always higher for diets 53:27 and 27:53 than they were for diets 80:O and 080. Different rates of disappearance must have been due to differences in the ruminal environment in which the AHP-WS was placed. The combination of AHP-WSas a readily available source of energy, and alfalfa as a source of DIP, macro and trace minerals, and cell content in diets 53:27 and 27:53 may have resulted in a more suitable environment for growth and metabolism of ruminal fibrolytic bacteria. This might explain the increased rates of digestion of DM and NDF seen with these diets. Brandt and Klopfenstein (4) offered a similar hypothesis to explain the positive associative effects observed between alfalfa and NH3:treated corn cobs on rate of in vitro NDF bgestion. Virtual absence of a lag phase for the two major components of WS hemicellulose, arabinose and xylose (Table 4), indicates extensive solubilization of hemicellulose by the AHP treatment process (10). The relatively high rates of disappearance of HNM compared with NDF in AHP-WS probably also is a function of the extensive solubilization and dis~ptionof hemicellulose by treatment with AHP. Estimates of extent of disappearance were quite high for all variables, ranging from approximately 100% for DM to 88% for

TREATED WHEAT STRAW-ALFALFA COMBINATIONS

arabinose. These percentages indicate the high degradability of AHP-WS. Lag time for in situ disappearance of alfalfa components Vable 5 ) was unaffected by diet; however, rate of ruminal digestion of alfalfa haylage (Table 5 ) was affected by differing dietary combinations in a manner similar to that observed for AHP-WS.Rates of DM, NDF, and galactose all responded in a quadratic manner, whereas xylose responded in a cubic manner to diet. Rates of component disappearance all were greater for diets containing combinations of the two forages than for those that contained only AHP-WS or alfalfa. The presence of AHP-WS as a readily available energy source in diets 53:27 and 27:53 may have improved microbial degradation of alfalfa. Silva and 0rskov (25) observed that the presence of a source of readily digestible cellulose and hemicellulose (such as AHP-WS)increased the numbers of fibrolytic ruminal microorganisms and, consequently, may improve digestibility of other less degradable fiber sources in mixed diets. Rates of disappearance of individual HNM were higher than those observed for NDF. Apparently, the hemicellulose fraction of alfalfa was more available than the cellulose fractions. The rates and extents of disappearance of arabiiose, galactose, and mannose all were relatively higher than that observed for xylose, indicating different availabilities of the constituent sugars of alfalfa hemicellulose. Wedig et al. (28) observed a significant increase in the xy1ose:arabiiose ratio of alfalfa with increasing ruminal incubation time. They suggested that the side chains of alfalfa xylans were hydrolyzed at a more rapid rate than the B1-4 linked xylose backbone. These data agree well with the greater rate and extent of arabinose compared with xylose disappearance observed in our study. The differences in extent of disappearance between DM (average 80%) and NDF (average 56%) indicate the large proportion of cell solubles and nuninally degradable protein present in the alfalfa. Approximately 40% of alfalfa DM was solubilized from 0-h bags. CONCLUSIONS

Positive associative effects were noted for both DMI and OMI by dairy heifers. The

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greatest increase in both OCCUZZed when the lowest level of alfalfa (27% of diet DM) was fed. Positive effects on intake in this study cannot be attributed to improved digestibility of dietary components. Digestibility of OM was similar across diets, averaging 63.6%. Additionally, digestibilities of NDF and ADF in diets containing combinations of the forages (53:27 and 27:53) were not different from those expected calculated from weighted means of forages in the blends. Improvements in intake may have been due to enhanced diet acceptability or a reduction in ruminal osmolarity due to a dilution of Na intake with increasing level of alfalfa. Ruminal LDR and PDR were unaffected by the addition of alfalfa. When combinations of forages were fed, maximum of digestible OM occurzed when the diet contained between 27 and 53% of AHP-WS.This suggests that the productivity of animals consuming high forage diets containing combinations of AHP-WS and alfalfa can be equal to that of animals fed high quality (22% CP) alfalfa alone. Given the right economic circumstances, feeding a 5050 combination (DM basis) of AHP-WS and alfalfa haylage in high forage diets could be an attractive option. Positive associative effects of combinations of the forages were noted for in situ rates of disappearance of both AHP-WS and alfaIfa haylage. Improvements in rates of disappearance for both substrates were facilitated by a ruminal environment more suitable for fiber digestion when both forages were fed than when they were fed alone. Alfalfa provided ruminally degradable protein and other nutrients, and AHP-WS provided a readily available source of energy. Additionally, AHPWS may have stimulated growth of fibrolytic microorganisms, which resulted in greater rates of disappearance of alfalfa when incubated in animals consuming blends of the forages. In vivo data from Experiment 1 indicated that no positive associative effect occurred for diet digestibility, whereas in situ data from Experiment 2 indicated positive associative effects on ruminal digestibility. These data are compatible if potentially digestible fiber leaving the rumen of heifers fed diets 80:0 and 0:80 was fermented in the hindgut. Hindgut fermentation then would have an equalizing effect on total tract digestibility. Journal of Dairy Science Vol. 74, No. 10. 1991

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ATwELt ET AL.

ACKNOWLEDGMENTS

ethylenediaminetefmacetatecomplex in feces. J. Dairy

Sci. 67:888. 13Kcrley, M. S., G. C. Fahey, Jr., L.L. Bergex, J. M. Godd, and P. L. Baker. 1985. Allcaline hydrogen peroxide treatment unlocks energy in agricultural byproducts. Science 230.820. 14Kerley. M. S, G. C. Fahey, Jr., L. L. Berm, N. R W e n , and J. M.Goald. 1986. Effects of sllraline hydrogen peroxide treatmat of wheat straw on site and extent of digestion in sheep. J. Anim. Sci. 63:868. 15-g. W. J.. D. N. Mowat, and W. K. Bilanski. 1971. Digestiility of sodium hydroxidbtreatedstraw fed alooe or in combition with alfalfa silage. Caa J. Anim. Sci. 51:743. REFERENCES 16 Mcrchen, N.R.,J. L.Firkins,and L.L. Beager. 1986. 1 Allen, M. S., and D. R. Mertens. 1988. Evaluating Effect of intake and forage level on ruminal hmover constraints on f i k digestion by rumen microbes. J. rates, bacterial protein synthesis and duodenal amino Nu@. 118:261. acid flows in sheep. J. Anim. Sci. 62:216. 2Association of Official Analytical Chemists. 1984. 17Mertens, D. R., and J. R. Loften. 1980. The effect of official methods of analysis. 14th ed. AOAC, Washstarch on forage fiber digestion kinetics in vitro. J. Dahy Sci. 63:1437. iogton, Dc. 3Berger. L. L.,T. I. Klopfemtein, and R A. Britton 18National Rescarch Council. 1985. Ruminant nitrogen 1980. Effect of sodium hydroxide treatment on rate of usage. Natl. Acad. Sci., Washington, DC. passage and rate of ruminal fiber digestion. J. Anim. 19National Research Council. 1989. Nutrient requireSci. 50745. ments of dairy cattle. 6th rev. d.Natl. Acad. Sci.. 4 Brandt, R. T., Jr.. and T. I. Mopfenstein. 1986. EvaluWashington, DC. ation of alfalfa-corn cob associative action. I. Interao 20Owens, F. N., and A. L. Goetsch. 1988. Ruminal tions between alfalfa hay and ruminal escape protein fermentation. Page 145 in The nlminant animal.D. C. on growth of lambs and stems. J. Anim. Sci. 632394. Church, 4.Prentice-Hall, Englewood Cliffs, NJ. 5 Cecava, M.I., N. R Merchen, L.L.Bergs, and G. C. 21 Patcrson, J. A., T. J. Klopfensteiu, and R. A. Bntton. Fahey. Jr. 1990. Intestinal supply of amino acids in 1982. Digestibility of sodium hydroxidatreated crop sheep fed allcaline hydrogen peroxide-treated wheat residues when fed with alfalfa hay. J. Anim. Sci. 5 4 straw-baseddiets supplemented with soybean meal or 1056. combinations of corn gluten meal and blood meal. J. 22Poppi. D. P.. B. W.Norton, D. J. Minson, and R.E. Anim. Sci. 68:467. Hendriclrsm. 1980. The validity of the critical size 6chancy, A. L.,and E. P. Mnrbach. 1%2. Modified theory for particles leaviog the rumen. J. Agric. Sci. reagents for determinationof urea and ammonia.Clin. (Camb.) W275. Chem. 8:130. 23Robertson, J. B.. and P. J. Van Soest. 1977. Dietary 'IGarleb, K. A., L. D. Bourquis and G. C. Fahey, Jr. fiber estimation in concenlrate feedstuffs. J. Anim. 1989. Neutral monosaccharide composition of various Sci. 45(Suppl. 1):254.(Abstr.) fibrous substrates: a comparison of hydrolytic proce24SASQDUser's Guide: Statistics, Version 5 Edition. dures and usc Of ani~n-e~chaoge h i g h - p d ~ m t ~ SAS Inst., Inc., Gary, NC. liquid chromatography with pulsed amperomtric d e 25 Silva, A. T.. and E. R 0rskov. 1988. Fibre degradation in the rumen of animals receiving hay, untreated tection of monosamharides. J. Agric. Food Chem. 37: 1287. or ammonia-treated straw. Anim. Feed Sci. Technol. 19277. SGoering, H. K.,and P. J. Van Soest. 1970. Forage fiber analyses (app.ratus, reagmts, procedures, and 26 Soofi, R.. G. C. Fahey, Jr., and L.L.Berger. 1982. I n some applications). Apic. Handbmk No. 379. ARSsiru and in vivo digstibilities and nutrient intakes by sheep of alkali-wated soybean stova. I. Anim. Sci USDA, Washington, DC. 55:1206. 9Gould J. M. 1984. Akalinr. peroxide delignification 27Uda1, P., P. E. Colucci, and P. J. Van Soest. 1980. of agriculhnal residues to enbance cnymatic saccharification. Biotechnol. Si-. 26% Investigation of chromhm, cerium and cobalt as markers in digesta rate of passage studies. J. Sci. Food lOGould, J. M., and S. N. Frta. 1984. High-eBliciency ethanol production from lignocellulosic residues pre Agric. 31:625. treated with aIkalim Hz02. Biotcchml. Bioeng. 26: 28 Wedig. C. L.,E. H.laster, and K. J. Moore. 1986. 628. Composition and digestibility of alfalfa and orchardgrass hemicellulose monosaccharides by Holstein 11 Grovum, W.L. 1987. A new look at what is controlling food intake. Page 1 in Feed intake by beef cattle. steas. J. Dairy Sci. 691309. F. N. Ow-, ed. Oklahoma State Univ. Press, Still29 Williams, C. H., D. J. David, and 0. Iismaa. 1962. water. The determination of chromic oxide in faeces samples l2Hart, S. P., and C. E. P o h 1984. Simultaoeous by atomic absorption spectrophotometry.J. Agric. Sci. extraction and determination of yaerbium and cobalt (Camb) 59381.

This study was supported in part by a gift from a consortium of hydrogen peroxide manufacturers (Degussa Corp., Allendale, NJ; E. I. Dupont de Nemours and Co. Inc., Wilmington, DE; FMC Corp., Rinceton, NJ). Appreciation also is extended to the Commodity Credit Corporation, USDA, for partial support of this project.

Journal of Dairy Science Vol. 74, No. 10, 1991