Densidad Del Sorgo

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R. S. Swingle, T. P. Eck, C. B. Theurer, M. De la Llata, M. H. Poore and J. A. Moore

digestibility by growing-finishing steersFlake density of steam-processed sorghum grain alters performance and sites of

1999. 77:1055-1065. J Anim Sci

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SWINGLE ET AL.1056

In the feedlot industry, considerable effort is expendedto regulate these var iables to achieve the desi reddegree of processing. Flake density ( FD ) a n d m ea s -ures of s tarch availabi li ty ( i.e ., suscept ibi li ty toenzymatic hydrolysis or degree of gelatinization) arecommonly used as tar get specifications for qualitycontrol in the feedmil l.

Given the emphasis on quali ty control in s team-

flaking of grains, and the t ime, effort , and expensespent to “optimally” process grains, there is surpris-ingly little published data relating the performance of cattle in the feedlot to the extent of steam-processingof corn (Zinn, 1990), and sorghum grain (Xiong et al.,1991; Reinhardt et al ., 1997; Theurer et al ., 1999).These studies report conflicting effects of varying FDon ADG and efficiency by growing-finishing steers.Zinn (1990) repor ted that decreasing FD of s team-processed corn from 360 to 257 g/L (28 to 20 lb/bu)increased tota l d igest ib ili tie s of s t a rch , CP, andenergy. There are no published data on the effect of flaking steam-processed sorghum grain to a range of densities on site and extent of nutr ient digestion. Thiss tudy was conducted to determine 1) the effect of s team-flaking sorghum grain over a range of flakedensities (sta rch availabilit ies) on performan ce andnut rient digestibility responses by growing-finishingsteers a nd 2 ) whet her different labora tory methods forevaluating starch availability in processed grains canbe used sa t isfactor i ly to es tabl ish FD cr i ter ia forquality control of the steam-flaking process.

Materials and Methods

Grain Processing and Starch Availability

Sorghum grain was steam-processed to FD of 412,360, 309, and 257 g/L (referred to respect ively asSF32 , SF28 , SF24 , a nd SF20 , reflect ing bushelweight in pounds, typical of field s tudies) us ing a46- × 76-cm roller m ill fitted with a 3-m sta inless steels t eam chest . S team was from a na tu ra l gas -fir edsteam generator. Grain was f laked a t leas t twice aweek and used immediately for preparation of diets.Flow of gra in in to the r ol lers was m ainta ined a t aconstant ra te to a l low a s teaming t ime of a pproxi-mately 40 min. Desired FD were achieved by progres-sively increasing tension on the rollers; processing wasalways in order from the most dense to least dense inorder t o maintain the desired intervals in degree of processing. Rol lers were preheated by processingabout 454 kg of grain prior to preparing experimentalflakes.

Each t ime grain was prepared, bulk density wasmeasured on whole dry grain and on flaked grain as itexi ted the rol lers . The DM was determined on thegrains a t each sta ge of processing (whole u nprocessed,steamed entering the rollers, and on flaked as it exitedthe rolle r s and as it was we ighed in to the d iet s ) .

Sa mples of ea ch F D wer e com posit ed over28-d periods and analyzed for starch availabili ty byquantifying glucose released and percentage of starchh yd rolyzed d ur in g 30-m in in cu ba t ion s wit hamyloglucosidase (Poore et al., 1989, 1991). Sampleswere also submitted to commercial laboratories forevaluation of relative starch availability by enzymatic(Nutrit ion-Labora tory Services, Inc. , Tolleson, AZ)

and loss of birefringence (High Plains Laborat ory,Hereford, TX) methods. Electrical load on the rollermill during production of each F D was measu red u singa n a m m et er.

Trial 1. Performance and Nu trient Digestibility by Feedlot Steers

Trials 1 and 2 were conducted with approval andunder the supervision of the University of ArizonaInst i tu t ional Animal Care and Use Commit tee . In a231-d feeding trial, 140 crossbred steer calves (about° t o Ô Brahman, wi th the remainder a mixture of

English and Continental breeds) were fed a growingdiet (1.17 Mcal NE g /kg DM, 50% flaked grain, 33%rough age) for t he first 112 d and a finishing diet (1.45Mcal NE g /kg DM, 78% flaked grain, 10% roughage)for the la s t 119 d (Tab le 1 ) . Each flake t r ea tmen t(SF32, SF28, SF24, or SF 20) was randomly assignedto five pens (weight replicates) of seven steers each.Roughage in both die ts was a mixture (equa l NDFbas is) of wheat straw and alfalfa hay. The roughageswere chopped using a rotor-type m ill (alfalfa, 15 cmscreen; wheat s t raw, 2 .5 cm screen). Animals weregiven ad libitum access t o feed, which was added t obu n ks a t 0700 a n d 14 00 d a ily.

Steers were weighed (pencil shrunk 4%) individu-ally on two consecutive days to start the experiment(mean ini t ia l weight , 181 kg) and on s ingle days a t28-d intervals. Final shrunk live weight was calcu-lated from hot carcass weight using a mean dressingpercentage (64.7%) across treatments. Group weights(s h r u n k 4 %) on ea ch pen , t a ken on t h e da y of shipment, were used to calculate dressing percentage.Steers were implanted with Ralgro (Mal linckrodtVeterinary Inc., Mundelein, I L) at the beginning of the exper iment and re implanted with Synovex ® -S(Syntex, Des Moines , I A) on d 85 and 169. Perfor-mance data were calcula ted from DMI and shrunk (4%) live weights. Estimated diet NE concentrationswere calculated from performan ce data using estab-lished energy relationships (NRC, 1984). Fecal grabsamples were taken from at least four steers in eachpen on d 42 of the 112-d growing pha se an d on d 88 of the 95-d fin ishing phase. Fecal samples were com-posited for each pen. Chromic oxide (.05% of DM,growing phase; .1% of DM, fin ishing pha se) wasadded to diets at least 5 d prior to fecal sampling as adigestibili ty mar ker.

Diet samples from each pen were dried at 55 ° C in aforced-air oven, a nd fecal samples were lyophilized








FLAKE DENSITY OF STEAM-PROCESSED SORGHUM 1057

Table 1. Ingredient comp osition and nutrient an alysesof growing and finishing diets (Trials 1 and 2)

aTrial 1: Growing diet fed d 1 through 112; finishing diet fed d113 through 231. Calculated NE g for growing a nd finishing diets

were 1.17 and 1.45 Mcal/kg DM, respectively.bSteam-flaked to densities of 412, 360, 309, and 257 g/L (32, 28,

24, and 20 lb/bu).cProvided 3,300 IU vitamin A an d 33 mg monensin/kg of diet

DM.

Diet a

Item Growing F in ish ing

% of DM

Composit ion (Trials 1 an d 2 )

Alfa lfa ha y 20.5 6.3Wheat stra w 12.2 3.5Steam-flaked sorghum grain b 50.0 78.3Cottonseed mea l 8.0 3.0Mola sses 4.0 4.0Anim al fa t 2.0 2.0Supplement c 1.0 1.0Lim estone .7 .9Urea .6 .5NaCl .5 .5Mono-, dica lcium phospha te .2 —Ch rom ic oxide (Tr ia l 1 ) .05 .1

Nutrient a nalysesTrial 1

DM, % 86.1 88.9

DM composition, %OM 92.8 95.5Starch 38.9 59.8Protein 14.3 12.9NDF 27.6 15.4

Gross energy, Mca l/kg 4.18 4.15Trial 2

DM, % 88.1 84.3Composition of DM, %

OM 92.7 95.6Starch 40.4 61.8Protein 14.6 12.8NDF 28.2 16.0ADF 19.2 14.7

Gross energy, Mca l/kg 4.14 4.11

prior to laboratory measurements . Diet and fecalsamples were ground to pass through a 2-mm screenin a Wiley Mill (Arthur H. Thomas Co., Philadelphia,PA) and then re-ground through a 1-mm screen in acyclone mill (Teca tor Cyclotec Model 1093, Hogan as,Sweden). F ina l DM was dete rmined by d rying a t100 ° C under vacuum. Nit rogen was determined byautomated procedures (Technicon, Tarrytown, N Y)after Kjeldahl digestion (AOAC, 1984). The NDF wasana lyzed accord ing to Rober t son and Van Soest(1981), using heat stable a -amylase ( Bacillus licheni- forms Type XII-A, Sigma Chemical Co., St. Louis,MO). Gross energy was determ ined by adiabatic bombcalor imetry (Par r Model 1241, Moline , IL) . Totals tarch was determined indirect ly as glucose (YSIModel 27, Yellow Springs Instrument Co., Inc., YellowSprings, OH ) following hydrolysis of samples usingamyloglucosidase (Diazyme L-200, Miles Inc., Elk-

hart , IN) according to the method described by Karre t a l . (1987) . Chromium was determined by a tomicabsorption spectrophotometry after wet ashing (Pooree t a l., 1991).

Data were an alyzed using a randomized completeblock design, with four t reatments in five blocks(weight replicat es), with pen a s the experimental u nit(Steel and Torr ie, 1980). Orthogonal polynomials

(linear, quadratic, and cubic components) were usedto characterize response curves, and orthogonal con-trasts were used to compare treatments. Cubic compo-nents are not given in the results because linear andquadra tic components a lmost a lways had lower pr oba-bili ty values. Orthogonal comparisons were SF32 vsSF28, SF24, and SF20; SF28 vs SF24 and SF20; andSF24 vs SF20 .

Trial 2. Nu trient Digestibilitiesin the Rumen and Intestines

Four crossbred steers (275 kg) fitted with cannulae

in the rumen, duodenum (flange approximately 5 cmfrom the pyloric sphincter), and ileum (flange approx-imately 60 cm from the ileocecal junction) were usedin a L at in s qu a r e d es ign . Th e obje ct ive wa s t oevaluate the effects of flaking sorghum grain to t hesame densi t ies as for the performance t r ia l (SF32,SF 28, S F24, a n d S F 2 0) on s it e a n d ext en t of digestion. Growing and finishing diets were the sameas in Trial 1 (Table 1). Digestibil it ies of the growingdiet ( fi rs t s tu dy) and of the fin ishing die t (secondst udy) were conducted with the same steers. Chromicoxide (.1% of DM) was included in the diets through-ou t each s tudy as a d igest ib ility marker.

Steers were kept in individual pens (2.5 × 5.0 m )with concrete floors and partial shade, and had freeaccess to water and t race-mineral ized sa lt b locks(provided 3,500 mg Zn, 2,000 mg Fe, 1,800 mg Mn,350 mg Cu, 100 mg I, and 60 mg Co per kg of block).Steers were fed t wice daily a t 0550 an d 1750. F eedoffered, r egardless of treatm ent, never exceeded themaximum intake established for each steer prior toinitiation of each study. In these digestibility studies,DMI averaged 6.8 and 6.4 kg/d for the growing andfinishing die ts , respect ively, and was 91 and 86%,respectively, of ad libitum intakes by feedlot steers fedt h es e s a me d iet s in Tr ia l 1.

Per iods of the Lat in square consis ted of 10 d of adaptation followed by 4 d of sample collection. Feedand ort samples were taken daily for 4 d. Samples of duodenal ( ∼300 m L) a nd ileal digesta ( ∼150 mL ) andfeces ( ∼250 g wet bas is) were col lected four t imesda ily ove r 3 d . These samples were immedia te lyplaced on ice. Collection t imes were moved forwa rd 2 heach day. This collection system provides a total of 12samples, representing each 2 h of a 24-h period. Feed,or t , d igesta , a nd fecal samples were kept frozen a t− 4 ° C until composited. These samples were pooled bys tee r with in per iods and then d r ied a t 55 ° C in a








SWINGLE ET AL.1058

Table 2. Dry matter content and starch availability measurements for sorghumgrain steam-flaked to different densities a

a Each value is the mean of eight samples (each sample pooled over 28-d periods). Grain DM prior toprocessing and prior to entering the rollers (mean ± SD) was 88.0 ± .39 and 81.8 ± .50%, respectively.Starch availability measures for unprocessed grain (mean ± SD) were: method 1, 202 ± 6.3 mg glucose/gDM and 25.3 ± 1.2% starch hydrolysis; method 2, 168 ± 12.2 mg glucose/g DM; birefringence method, 10 ±

2.3 gelatinization.bSF32, SF28, SF24, and SF20 = steam -flaked a t den sities of 412, 360, 309, and 257 g/L (32, 28, 24, and

20 lb/bu ), r espectively.cDept. Anim. Sci., Univ. Arizona, Tucson: incubation with amyloglucosidase for 30 min.dNutr ition-Laborat ory Services, Inc., Tolleson, AZ: incubation with Taka -Diastas e (cont ain s a -amylase

and other amylolytic, pr oteolytic, an d lipolytic enzymes from Aspergillus oryzae ) .eHigh Plains Laboratory, Inc., Hereford, TX: loss of microscopic birefringence (percentage of starch

granules gelat inized).yLinear effect of f lake density ( P < .05).zQuadratic effect of flake density ( P < .05).

Flake density b

Item SF32 SF28 SF24 SF20 SEM

Grain DM, %E xit ing rollers 82.6 82.9 83.5 83.9 .1E nter ing diet s 82.9 83.3 83.9 84.3 .1

Star ch availabilityEnzyme method 1 c

Glucose release, mg/g grain DM yz 531 614 684 730 7.8Percentage starch hydrolysis yz 67.6 75.4 83.2 88.1 .8

Enzyme method 2 d

Glucose release, mg/g grain DM y 283 321 376 413 3.9

Birefringencee

Percentage gelatinization yz 52.6 54.6 54.9 55.3 .4

forced-ai r oven for 48 h . Sample processing andanalytical methods for starch availability, DM, OM, N,NDF, starch, GE, and chromium are described in Trial1. The ADF was analyzed using the methodology of Goering and Van Soest (1970). Data for each study(growing and finishing) were separately analyzed asa 4 × 4 Latin square using SAS (1985). Orthogonalpolynomials and orthogonal comparisons are described

in Tr ia l 1 .

Results and Discussion

Starch Availability

Char acteristics of grain flaked to different densitiesar e present ed in Table 2. Moisture conten t of the gra inwas increased from 12% to a pproximat ely 17% duringexposure to steam. Starch availability, as measured byeach of the laboratory methods, increased linearly orquadratically ( P < .05) in response to increased extent

of processing (decrea sed F D), with SF32 always beingthe lowest value and SF20 the highest value. Therange of responses was much greater for enzymaticmethods than for gela t in izat ion based on loss of b irefr ingence. Table 3 shows corre la t ions amonglaboratory measures of s tarch availabi li ty. Flakedensity was more highly correlated with enzymaticmeasures of starch availabili ty than with percentagegelatinization determined as loss of birefringence (R 2

= .87 to .92 vs .36, respectively), and the enzymaticmethods were highly correlated with each other (R 2 =.90 to .93) . Xiong e t a l . (1990a) a lso found tha tenzymatic methods are more sensitive than gelatiniza-tion. Other studies have demonstrated that decreasingFD linear ly increases in vitro ra te of star ch hydrolysisin grains by amylolyt ic enzymes (Theurer, 1986;Xiong et al., 1990a,b; 1991; Zinn, 1990; Theurer et al.,

1999).We emphasize that the data from the present study

were determined from grain flaked to different densi-ties in a single mill, under controlled conditions, andover relatively short periods of t ime. Other factors,including initial density and moisture content of thegrain, steam ing time, level of moisture addition, andcondition of the rollers, affect laboratory measures of s tarch availabi li ty a t a g iven FD (Karr , 1984). Weconclude tha t the enzymat ic l abora tory me thodscommonly used to evaluate s tarch availabi li ty inprocessed grains can be used sat isfactorily to esta blishFD criteria for quality control of t he steam-flakingprocess.

Trial 1. Performance and Nu trient Digestibility by Feedlot Steers

Per formance da ta for growing (d 1 to 112) andfinishing (d 113 to 231) phases and for the ent irefeeding period (d 1 to 231) are in Table 4. The largestand most consistent response to increased extent of









Table 3. Correlations (R 2) am ong starch availability m easurementsfor sorghum grain steam-flaked to different d ensities a

aNumber of observations per measurement = 32 (four f lake densit ies × eight sampling periods).bDept. Anim. Sci., Univ. Arizona, Tucson: incubation with amyloglucosidase for 30 min.cNutr ition-Laborat ory Services, Inc., Tolleson, AZ: incubation with Taka-Diastase (conta ins a -amylase and other amylolytic, pr oteolytic,

and lipolytic en zymes from Aspergillus oryzae ) .dHigh Plains Laboratory, Inc. , Hereford, TX: loss of microscopic birefringence (percenta ge of starch granules gelat inized).

Measurement

Flake Enzym e E nzyme Enzym e Percen tdensity, method 1a , meth od 1b, method 2, gela t in -

Measurem ent g/L m g/g % mg/g iza t ion

F la ke density, g/L 1.00 .88 .87 .93 .36Enzyme method 1a b, mg glucose/g gra in DM .88 1.00 .90 .90 .36Enzyme method 1b b, percen ta ge sta rch hydrolysis .87 .90 1.00 .93 .39Enzyme method 2 c, mg glucose/g gra in DM .93 .90 .93 1.00 .46Birefringence m ethod d percenta ge gela t in iza tion .36 .36 .39 .46 1.00

processing (decrea sing F D from SF32 to SF 20) was alinear ( P < .05) decrease in DMI, expressed either askilograms per day or as a percentage of BW. Depres-

s ion in DMI was a lmost twice as great when s teerswere fed finishing diets (13 %) than when steers werefed growing die ts (7%). Xiong e t a l . (1991 ) , Rein-ha rd t e t a l . (1997) , and Theure r e t a l . (1999) a l soreported linear decreases in DMI by feedlot steers asFD of steam-flaked sorghum decreased. In the finish-ing phase and for the ent ire t r ia l, ADG decreasedlinearly ( P < .05) as FD decreased, which resulted ina linear decrease ( P < .05) in final live weights. In thegrowing phase, the efficiency (DMI/gain) response todecreasing FD was a curvilinear decrease (qua dra tic,P < .05), with the lowest value (most efficient) forSF28 and the highest value (least efficient) for SF32.The efficiency responses in the finishing pha se andoverall tria l followed a similar patt ern ( P > . 10). Themajor change in efficiencies in the growing andfinishing phases and the 231-d trial occurred betweenSF32 and SF28; efficiencies for SF28, SF24, and SF20were very similar. The major change in gain/DMI inthe s tudy by Xiong e t a l . (1991) was between SF34and SF28 .

The response pattern of ADG and efficiency in otherFD s tudies is not cons is t en t . Xiong e t a l. (1991)reported th at lowering FD (SF 34 t o SF22) resulted ina linear increase in efficiency by feedlot steers, but no

change in ADG. Reinhard t e t a l . (1997) r epor t edl inea r decreases in da ily ga in , but no changes inefficiency, with decreasing sorghum FD (SF28 toS F 2 2). T he ur er e t a l. ( 1 9 9 9 ) n ot ed a n u m er ica ldecrease in ADG ( − 4%) and improvement in efficiency(+4%) by steers as density of steam-flaked sorghumdecreased from SF30 to SF20. Est imated NE m andNE g values for the growing and finishing diets (Table4 ) also showed a tendency for a curvilinear responseto FD, although the quadratic component was statisti-cally significant ( P < .05) only for the growing diet.The NE m and NE g concentrations for the growing dietwere h ighest for SF28; for the finishing diet, NE m and

NE g content was lowest for SF32. As with DMI/gain,the largest changes in estimated NE concentrat ionsfor both diets were between SF32 and SF28. Ratios of

d ie t NE values est imated from performance to NEva lu es ca lcu la t ed fr om t h e N RC ( 1 9 8 4 ) for t h egrowing diet were greater than 1:1 for all FD (average= 1.045), with the highest values for SF28 and SF24(Table 4). In contra st , estimated/calculated NE rat iosfor fin ish ing d ie t s were le ss than 1 :1 for a ll FD(average = .968), with the lowest values for SF32. Itseems likely that the feedlot performance responses toincreased degree of grain processing ar e influenced bylevel of roughage in the diet . Estimated NE intakeswere highest for SF28 and lowest for SF20, whensteers were fed th e growing and finishing diets (dat anot shown). Mean NE g values for SF32, SF28, SF24,and SF20, respectively, for the growing diet were 6.0,6.2, 5.8, 5.4 Mcal/d and for the finishing diet were 5.8,6.0, 5.7, 5.1 Mcal/d. Thus, NE g in takes seemed todecrease in a more curvil inear manner than DMI,which was linea r, w ith decreasing FD.

With the except ion of ca rcass weigh t , wh ichdecreased linearly ( P < .05) in response to increasedextent of processing, car cass char acteristics were notinfluenced by FD (Table 5) . Percentage of pelvic,kidney, a nd hear t fa t tended to decrease ( P < .10)with decreasing FD. The percentage of carcassesgrading low choice or bet ter (data not shown) was

highest (53%) from steers fed SF32, SF28, and SF24,and lowest (31%) for steers fed SF20 ( P = .10). In t hep re se nt s t ud y, t h is cou ld h a ve be en r ela t ed t odifferences in carcass weight, but Xiong et al. (1991)also observed a tendency for improved choice percen-tage when steam-flaked sorghum grain with a heavierFD (SF34 vs SF28 or SF22) was fed. Theurer e t a l .(199 9) reported t hat dressing percentage and carcassfat thickness decreased linearly as FD decreased fromSF30 to SF20. Reinhardt et al . (1997) also found thesame dressing percentage response, but reported nodifferences in carcass merit due to varying sorghumFD.








SWINGLE ET AL.1060

Table 4. Feedlot performance of crossbred steers fed diets containing sorghumgrain steam-flaked to different densities (Trial 1)

a SF32, SF28, SF24, and SF20 = steam -flaked a t den sities of 412, 360, 309, and 257 g/L (32, 28, 24, and20 lb/bu ), r espectively.

bLive weights reduced 4% t o account for gastrointestina l fill.cFinal l ive weight (231-d) calculated as hot carcass weight/.647.dRatio of NE estimated from performance to NE calculated from NRC (1984 ).yLinear effect of f lake density ( P < .05).zQuadratic effect of flake density ( P < .05).

Flake density a

Item SF32 SF28 SF24 SF20 SEM

Pen replica tes, n 5 5 5 5 —

Live weight, kgInitial b 182 181 182 180 1112-d b 354 357 353 344 4Final cy 486 488 477 463 6

DMI, kg/d1− 112 d y 7.72 7.50 7.36 7.18 .12113 − 231 d y 7.91 7.59 7.27 6.91 .131− 231 d y 7.82 7.54 7.32 7.04 .11

DMI, % BW1− 112 d y 2.88 2.78 2.76 2.75 .03113 − 231 d y 1.89 1.80 1.75 1.71 .03

1− 231 dy

2.34 2.26 2.18 2.19 .02Daily gain, kg

1− 112 d 1.54 1.57 1.52 1.46 .03113 − 231 d y 1.11 1.10 1.05 1.00 .031− 231 d y 1.31 1.32 1.28 1.22 .03

DMI/gain1− 112 d z 5.03 4.78 4.84 4.92 .06113 − 231 d 7.15 6.95 6.91 6.92 .191− 231 d 5.95 5.70 5.71 5.75 .08

Diet NE m , Mcal/kg1− 112 d z 1.83 1.91 1.89 1.85 .02113 − 231 d 1.98 2.09 2.11 2.11 .06

Diet NE g, Mcal/kg1− 112 d z 1.21 1.28 1.25 1.21 .02

113 − 231 d 1.34 1.43 1.45 1.43 .05NE estima ted/calculated d

NE m1− 112 d 1.01 1.06 1.04 1.02 —113 − 231 d .93 .98 .99 .98 —

NE g1− 112 d 1.03 1.09 1.08 1.03 —113 − 231 d .91 .98 .99 .98 —

The greatest changes in nutrient digestibil i t ies bysteers in the feedlot occurred as FD was decreasedfrom SF32 to SF28, with both diets (Table 6). Fecalstarch concentrations decreased linearly and apparentdigestibilities of starch increased linearly in responseto increased degree of gra in pr ocessing in the growingand finishing periods ( P < .05). Fecal star ch was twiceas high for SF32 when st eers were fed the growing

compared to the fin ishing die t , result ing in s tarchdigestibilities of 92 and 98%, respectively. With highroughage diets, SF32 ma y not be adequat ely processedto appr eciably improve sta rch digestibility over t hat of dry-rolled sorghum (90 and 87% for Theurer, 1986,and Huntington, 1997, respectively). Decreasing FD

decreased linear ly ( P < .05) t he NDF digestibilities inthe finishing diet only. Digestibilities of DM, CP, andGE increased linearly ( P < .05) with decreased FD inthe growing diet, but not the finishing diet . The DE(Mcal/kg) increased linearly with decreasing FD forthe growing die t , but decreased l inear ly with thefinishing diet ( P < .05). The la t t e r was due to thelowest GE digest ib il ity for SF20 and the very low

digest ib il it ies of NDF for SF24 an d(or) SF20.Characteristically, electrical energy requirements

(data not shown) for processing increased linearly ( P< .05) as FD decreased (20.4 , 22.0, 26.2, and 30.6amps for SF32, SF28, SF24, and SF20, respectively).Electr ical energy requirement s for processing SF20 vs









Table 5. Carcass measurements of crossbred steers fed diets containingsorghum grain steam-flaked to different densities (Trial 1)

aSF32, SF28, SF24, and SF20 = steam -flaked a t densities of 412, 360, 309, and 257 g/L (32 , 28, 24, an d20 lb/bu), r espectively.

b(Hot carcass weight/l ive weight ) × 100.cKidney, pelvic, and heart fat , percentage of carcass weight.dCoded: 4.00 = sl ight 00, 5.00 = sma ll 00.eCoded: 9.00 = select 00, 10.00 = choice 00.f Linear effect of f lake density ( P < .05).gQuadratic effect of f lake density ( P < .05).h Quadratic effect of f lake density ( P < .10).

Flake density a

Item SF32 SF28 SF24 SF20 SE M

P ens (s t ee r s ), n 5 5 5 5 —Hot carcass weight, kg fg 314.4 315.6 308.8 299.8 3.8Dressing percentage b 64.7 64.9 64.5 64.7 .2Fa t th ickness, cm 1.27 1.34 1.31 1.35 .07Ribeye area, cm 2 78.9 78.5 81.4 78.0 1.3KP H c, %h 3.0 2.8 2.7 2.8 .08Marbling score d 5.14 4.94 5.07 4.87 .16USDA Quali ty Grade e 9.24 8.76 9.28 8.60 .29USDA Yield Grade 3.08 3.12 2.88 3.06 .08

Table 6. Dry matter intake, fecal starch concentrations, and nutrient digestibilities by steers fed dietscontaining sorghum grain steam-flaked to different densities (feedlot conditions) (Trial 1)

aSF32, SF28, SF24, and SF20 = steam-flaked at densit ies of 412, 360, 309, and 257 g/L (32, 28, 24, and 20 lb/bu), respectively.bSF32 vs SF28, SF24, and SF20 ( P < .05).cSF28 vs SF24, and SF20 ( P < .05).dSF24 vs SF20 ( P < .05).yLinear effect of f lake density ( P < .05).zQuadratic effect of f lake density ( P < .05).

Growing diet a Finishing diet a

Item SF32 SF28 S F24 S F20 S EM SF 32 S F28 S F24 S F20 SEM

DMI, kg/d 7.7 7.5 7.2 7.1 .1 bcy 8.0 7.5 7.3 6.9 .3 b

F eca l sta rch , % DM 7.6 3.6 2.7 2.3 .3 yz 3.8 2.8 2.4 2.1 .3 y

Digestibility, %DM 55.8 59.6 59.3 60.8 .9 by 67.9 67.7 66.3 64.3 1.3Sta rch 91.6 96.2 97.2 97.7 .4 bcyz 98.0 98.5 98.6 98.8 .2 by

CP 49.1 54.2 51.0 53.5 .8 bdy 43.1 46.6 45.1 46.1 2.2NDF 21.5 21.8 23.1 22.5 2.6 15.1 7.2 1.2 − 1.5 4.9 by

GE 53.9 58.7 59.6 60.5 1.1 by 67.3 67.9 66.7 65.1 .9

DE, Mcal/kg 2.24 2.43 2.52 2.54 .05 by 2.81 2.82 2.77 2.69 .04 y

SF32 increased by 50%, but these requirements forprocessing SF28 vs SF32 increased by only 8%. Oth ers tudies have demonstra ted increased costs as FD isdecreased (Karr, 1984; Xiong et al., 1990a; Reinhardte t a l ., 1997) . In the present s tudy, dai ly gains werenot decreased when steers were fed SF28 compared toSF32. Considering increased processing costs, SF28would be the most efficient FD, because the greatestimprovements in feed conversion occurred when FDwas reduced from SF32 to SF28 .

In t he present st udy, starch a vailability (measu redby laboratory methods, and as evidenced by decreasedfecal starch concentrations and higher digestibility of s ta rch) increased l inear ly as FD of sorghum grain

decreased, but electrical energy use for processing alsoincreased l inear ly. The DMI and ADG decreasedlinear ly as degree of processing increased, resu lting inlighter final l ive weights. Feed efficiency and esti-mat ed diet NE responses to increased grain processingtended to follow a curvilinear patt ern, being impr ovedmost when FD was decreased from SF32 to SF28.Reduced feed efficiency and lower es t imated NEvalues for the growing diet with SF20, a s comparedwith SF28 and SF24, is evidence that sorghum grain

can be “over processed.” Roughage source and levelmay be major factors that influence the performanceresponse by feedlot cattle to differences in degree of s team-flaking of sorghum grain .









Table 7 . Nu trient intakes and digestibilities by steers fed diets containing sorghumgrain steam-flaked to different densities (Trial 2)

Growing diet a Finishing diet a

Item SF32 SF28 SF24 SF20 SE M SF 32 SF28 SF24 SF20 SEM

DMInta ke, g/d 6,790 6,706 6,771 6,814 123 6,228 6,473 6,413 6,368 67 b

Flow, g/dDuodenum 4,377 4,172 4,398 4,233 195 3,483 3,223 3,410 3,215 121Ileum 2,686 2,607 2,889 2,862 151 1,995 1,775 1,898 1,800 58 b

Feces 2,222 2,218 2,267 2,334 114 1,520 1,440 1,333 1,350 86

Digestibility, % of intakeRumen 35.0 37.9 34.2 37.7 2.5 43.7 49.5 46.0 49.3 1.4 bx

Rumen + small intest ine(S I ) 60.4 61.1 56.7 58.1 2.4 67.7 72.3 70.2 71.7 .6 byz

Tota l t ract 67.2 67.1 66.4 65.9 1.2 75.5 77.5 79.1 78.8 1.2 cx

StarchInta ke, g/d 2,771 2,672 2,742 2,753 77 3,829 4,001 3,934 3,984 41 b

Flow, g/dDuodenum 466 290 302 232 66 bx 694 466 534 371 84 by

Ileum 115 52 64 56 8 byz 221 140 169 94 38 cx

Feces 30 17 18 17 2.4 by 95 74 46 44 15 by

Digestibility, % of intakeRumen 83.0 89.4 88.8 91.6 2.2 by 81.6 87.9 86.2 90.6 2.2 by

Rumen + SI 95.8 98.0 97.6 98.0 .3 byz 94.1 96.3 95.6 97.6 1.0 cx

Tota l t ract 98.9 99.4 99.3 99.4 .1 byz 97.5 98.1 98.8 98.9 .4 by

Digestibility, % of entryinto intest ineSma ll in test ine 72.9 79.8 78.7 76.1 4 .0 70.2 71.1 69.4 74.5 5 .0La rge in test ine 73.5 66.6 68.2 70.3 2 .4 55.5 46.9 70.1 47.9 6 .4

CPIntake, g/d 986 1,006 984 996 15 796 825 798 845 13 ex

Flow, g/dDuodenum 1,207 1,130 1,167 1,154 40 1,015 975 960 1,036 24 z

Ileum 410 383 384 353 11 by 327 315 309 279 9 by

Feces 400 381 371 366 16 375 348 325 320 11 by

Digestibility, % of intakeRumen − 23.3 − 12.6 − 19.5 − 16.3 3.1 − 28.4 − 20.3 − 21.8 − 23.2 3.7Rumen + SI 58.5 61.8 60.8 64.5 1.2 by 58.5 61.1 60.7 67.0 1.2 bey

Tota l t ract 59.3 62.3 62.1 63.3 1.3 x 52.8 57.2 59.2 62.0 1.5 by

ND FInta ke, g/d 1,975 1,862 1,900 1,882 66.5 1,006 1,074 1,039 963 21 dez

Flow, g/dDuodenum 1,433 1 ,472 1 ,463 1 ,477 9 8 775 749 942 775 56Ileum 1,383 1,368 1,530 1,533 98 854 767 936 818 51Feces 1,298 1,301 1,351 1,357 79 662 649 613 590 64

Digestibility, % of intakeRumen 27.4 21.0 21.4 21.1 5.7 21.3 28.9 7.0 18.9 4.2 d

Rumen + SI 30.1 26.4 16.7 18.5 7.0 14.1 27.3 8.7 14.5 3.1 d

Tota l t ract 34.4 30.2 28.7 28.1 3.3 32.8 38.2 40.4 38.8 5.3

ADFInta ke, g/d 1,338 1,292 1,299 1,252 51 616 661 642 620 17

Flow, g/dDuodenum 1,069 1,086 1,048 1,167 113 446 478 561 496 41Ileum 988 987 965 1,062 51 517 454 523 491 23Feces 979 946 968 988 61 425 423 390 393 38

Digestibility, % of intakeRumen 20.2 15.6 24.7 15.7 5.6 26.3 26.6 9.8 19.8 5.4Rumen + SI 26.4 22.7 27.4 15.2 4 .8 15.3 30.4 17.5 20.3 2 .8 d

Tota l t ract 26.9 26.7 27.8 21.5 3.0 29.5 35.1 38.8 36.5 4.6(cont inued)








SWINGLE ET AL.1064

Table 7 (continued) . N utrient intakes and digestibilities by steers fed diets containing sorghumgrain steam-flaked to different densities (Trial 2)

GEIntake, Mca l/d 28.0 27.8 27.9 28.4 .6 25.9 26.5 26.4 26.0 .2 cz

Tota l t ract digestibility, % 65.8 65.2 64.7 63.8 1.1 72.9 75.1 77.5 75.9 1.3 c

DE, Mca l/kg diet 2.71 2.70 2.67 2.65 .03 3.03 3.08 3.19 3.11 .06

a SF32, SF28, SF24, and SF20 = steam-flaked at densit ies of 412, 360, 309, a nd 257 g/L (32, 28, 24, a nd 20 lb/bu), respectively.b,c SF32 vs SF28, and SF24, and SF20 ( P < .05 and P < .09, respectively).dSF28 vs SF24 and SF20 ( P < .05).eSF24 vs SF20 ( P < .05).x,y Linear effect of f lake density ( P < .09 and P < .05, respectively).zQuadratic effect of flake density ( P <.05).

steers were fed diets containing alfalfa hay, or wheats t raw and a l fa l fa (same die t as current s tudy) . Thispat tern was r eversed when s teers were fed th e die tcontaining cottonseed hulls. The effect of FD on NDFand ADF digestibili t ies may differ with sources of

dietary roughages.Digestibilities of GE did not differ with FD whensteers were fed the growing diet, but were increasedquadrat ical ly ( P < .05, S F32 wa s l ow es t ) wit hdecreasing FD when finishing diets were fed. Dietaryconcentrat ions of DE were n ot affected by F D (2.68and 3.10 Mcal/kg DM for the growing and finishingdiets, respectively). With the finishing diet , DE waslowest for SF32 and greatest for SF24, which agreeswith the estimated diet NE in the performance trial .

Total tra ct digestibili t ies by intact feedlot steers(Trial 1) for DM, CP, NDF, and GE were considerablylower than digestibilities determined with cannulateds tee r s (Tr i a l 2 ) . The e ffect of FD on feca l s t a rchconcentra tions a nd t otal sta rch digestibilities were th eonly measurements that were consistent for both dietsin Trials 1 and 2. These differences may reflect the 9to 16% higher DMI for the intact steers compared tothe cannulated s teers , and the sampling techniques .Twelve fecal samples were obta ined in Tr ia l 2 a tvarious hours over a 3-d period, but obtaining fecalsamples for only one day under feedlot conditions(Trial 1 ) may not provide accurat e digestion coeffi-cien ts for DM, CP, fiber, and energy. Nut r ien tdigestibilities of starch a nd pr otein in the total t ra ct of s teers in the more control led condit ions of Tr ia l 2agree more closely with previous values for steam-flaked sorghum grain (Theurer, 1986; Rahnema et al.,1987a,b; Theurer et al., 1996; Huntington, 1997) thando digestibility values obtained under feedlot condi-t ion s (Tr i a l 1 ) .

In conclusion, decreasing FD of steam-processedgrain in the present digestion studies had the greatesteffects on star ch a nd protein digestibilities by steersfed the growing and finishing diet . The most consis-tent responses were for s tarch digest ib il it ies . Thesimultaneous increase in digestibilities of starch and

CP at var ious s ites within the digest ive t ract whensorghum grain is extensively processed is probablydue to the disruption of the protein m atrix associatedwith the s tarch granules wi thin the kernel (Rooneyand Pflugfelder, 1986). This disorganization of protein

matrix and starch granules allows increased suscepti-bility of the protein a nd starch to ru men microbial,pancreatic, a nd intestinal enzymes. As density of thegrain was reduced from SF32 to SF20, values wereincreased l inear ly for s tarch digest ib il it ies in therumen by 10%, rumen plus small intestine by 3%, andtota l t ract by 1%. Greater ruminal s tarch digest ioncan result in improved feed convers ions and netabsorption of energy (Theur er et al ., 1996). Digesti-bi l i t ies of CP in the rumen plus smal l in tes t ine andtota l t r act were linea r ly increased by 8 and 15%,respectively, for steers fed both diets. Because greatestimprovements in s tarch and CP digest ib il it ies oc-curred when density was lowered from SF32 to SF28,op t ima l sorghum gra in FD was SF28 .

Implications

Th e op tim a l fla k e ( b u l k ) d en s it y for s t ea m -processed sorghum grain a ppears to be 360 g/L (2 8 lb/ bu ), based on performa nce by feedlot steers, grainprocessing costs, and diet digestibilities of protein andstarch. Fur ther decreases in flake density wil l notappreciably increase net energy value of the grain or

improve feed convers ions . Flaking to very l ightdensities (i.e., 257 g/L or 20 lb/bu) may result in “overprocessed” grain when compared to flake densities of 360 and 309 g/L (28 and 24 lb /bu), r e su lt ing ininferior feedlot performa nce. Decreasing flake densitywil l consis tent ly increase ruminal and tota l s tarchd igest ib ilit ie s by s t ee r s. Enzymat ic labora torymethods commonly used to evaluate starch availabil-i ty (hydrolysis) are effect ive in es tabl ishing flakedensity criteria for quality contr ol of the steam -flakingprocess . F lake dens ity is more closely r e la t ed toenzymatic methods than to percentage gelatinization.









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