Supplementing Maize or Soybean Hulls to Cattle Fed Rice Straw: Intake, Apparent Digestion, In situ Disappearance and Ruminal Dynamics*

Transcription

1 807 Asin-Aust. J. Anim. Si. Vol. 21, No. 6 : June Supplementing Mize or Soyen Hulls to Cttle Fed Rie Strw: Intke, Apprent Digestion, In situ Dispperne nd Ruminl Dynmis* Nguyen Tien Von 1, Dvid G. St. Louis**, Adm I. Orr nd Brin J. Rude Deprtment of Animl nd Diry Sienes, Mississippi Stte University, Mississippi Stte, MS, 39762, USA ABSTRACT : Steers with d liitum ess to rie strw were ssigned to four diets to evlute the effets of mize or soyen hull supplementtion on intke, in vivo digestiility, ruminl ph, VFA, mmoni-nitrogen (NH 3 -N) nd in situ ruminl dispperne of feed nutrients y ttle onsuming rie strw. Supplement tretments were: no supplement (); soyen mel t 0.127% BW (); rked mize t 0.415% BW plus 0.044% BW soyen mel (); or soyen hulls t 0.415% BW plus 0.044% BW soyen mel (). The nd diets were formulted to provide pproximtely 4 MJ of NE m per kg of diet. Rie strw DMI ws not ffeted (p = 0.34) y supplement. Apprent dry mtter (DM) digestiility ws greter (p<0.001) for nd (56.6 nd 60.0%, respetively) thn for steers onsuming or (51.8 nd 44.4%, respetively). Apprent NDF digestiility ws greter (p<0.0004) for thn (61.7 vs. 58.0%, respetively) nd pprent ADF digestiility ws greter (p<0.0008) for thn (61.1 vs. 49.2%, respetively). There ws no differene in pprent hemiellulose digestiility (p = 0.43). Anlysis of ruminl fluid olleted 0, 2, 4, 6, nd 8 h post-feeding reveled mmoni-nitrogen ws gretest (p<0.05) for steers on nd diets t 2 h (24.08 nd mg/dl, respetively) nd totl voltile ftty ids ws gretest (p<0.05) for t 4 h (230 mm/l). In situ dispperne, mesured t 0, 2, 4, 6, 8, 16 nd 24 h, indited tht, nd tended to enhne the digestiility of DM nd fier omponents of rie strw. In situ dispperne of rie strw DM ws gretest for nd/or from 4 to 24 h (p = 0.03). Rie strw NDF nd ADF dispperne ws enhned y supplementtion from 16 to 24 h (p<0.02). Rie strw DM, NDF nd ADF disppernes t 24 h were similr for nd tretments. When feeding ttle rie strw diets, energy nd proteinsed supplements re essentil. This study showed tht fier-sed supplements re just s, if not more, effetive s strh-sed supplements in rie strw utiliztion. This study shows tht soyen hulls, in spite of their high fier ontent, re s effiient s mize for supplementing rie strw primrily euse fier in soyen hulls is highly digestile s shown y in vivo digestiility nd in situ dispperne. (Key Words : Supplementtion, Rie Strw, Soyen Hulls, In situ Dispperne, Ruminl Metolism) INTRODUCTION Rie strw (Oryz stiv, IRN: ) is onsidered poor qulity forge for ruminnts ut is produed in undne throughout the rie growing res of the tropis nd sutropis. Better qulity forges re usully ville in temperte ountries so rie strw s feed hs not een given muh ttention y ttle (Bos turus) produers or niml sientists. However, refuse urning is eoming more restritive, nd s result, rie produers in the USA re fing eonomi nd environmentl prolems of rie * Journl rtile J11182 of the Mississippi Agriulturl nd Forestry Experiment Sttion, Strkville, Mississippi. ** Corresponding Author: Dvid G. St. Louis. Tel: , Fx: , E-mil: stlouis@r.msstte.edu 1 Hue University of Agriulture nd Forestry, 24 Phung Hung Street, Hue City, Vietnm. Reeived Septemer 14, 2007; Aepted Deemer 23, 2007 strw disposl. Rie strw hs een suessfully treted with ure to improve fier digestiility (Wnpt, 1990; Elseed et l., 2003), improving its use s ttle feed nd in turn serve s n dditionl soure of revenue for rie produers. Supplementtion strtegies hve lso improved the utiliztion of rie strw (Prdhn et l., 1996; Chowdhury, 2001). Cttle fed medium or low qulity forges respond differently to types nd mounts of energy supplements. Redued intke nd fier digestion of low qulity forges with mize (Ze mys, IRN: ) supplementtion is well doumented (Snson et l., 1990; Higgins et l., 1991; Grés-Yépez et l., 1997). It hs een shown, however, tht supplementtion with soyen hulls (Glyine mx, IRN: ) does not ffet intke or digestiility of forges (Mrtin nd Hierd, 1990; Wheeler et l., 1999; St. Louis et l., 2002). Assoitive effets etween low qulity forges nd supplements with different nutrients re not

2 808 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): Tle 1. Nutrient omposition (%, DM) of rked mize, soyen hulls, soyen mel, nd rie strw fed to steers for different tretments 1 Feedstuffs offered (%) Nutrient Crked mize Soyen hulls Soyen mel Rie strw DM OM Ash NDF ADF CP Tretment diets on DM sis: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with well estlished. First, Ntionl Reserh Counil (1996) equtions sed on NE m fil to urtely predit dry mtter intke (DMI) of eef ttle fed ll-forge diets. Seond, supplements re often predited y these equtions to sustitute for forges in the totl diet, not llowing for dditive effets on intke (St. Louis et l., 2002). In ompnion studies, Orr et l. (2007) nd Nguyen et l. (2007), found tht supplementing soyen hulls or mize enhned totl trt digestiility of low qulity ermudgrss hy (Cynodon dtylon, IRN: ). In the sme studies they found tht soyen hulls, in spite of their high fier ontent, resulted in more rpid in situ dispperne of hy onstituents, while produing greter volume of totl VFA in the rumen. Their dt lso suggest tht, when fed t lest 0.5% of BW, soyen hulls re more effiient thn mize s supplement in feeding systems using low qulity forges euse of their dditive nd ssoitive effets. The ojetive of this tril ws to evlute the effets of mize or soyen hull supplementtion on intke, in vivo digestiility, ruminl ph, voltile ftty ids (VFA), mmoni-nitrogen (NH 3 -N), nd in situ ruminl dispperne of feed nutrients y ttle onsuming rie strw. MATERIALS AND METHODS Animls nd experimentl design Four steers were ssigned to one of four diets during four onseutive 24-d periods using 4 4 Ltin squre to evlute pprent nutrient digestiility, ruminl environment, nd in situ ruminl digestiility of individul feeds. Angus, Hereford, nd(or) Chrolis steers with ruminl nnule (initil BW 225±18.9 kg) were fed rie strw d liitum nd were ssigned to one of four tretments, reeiving new supplement eh period. Tretments were: no supplement (); soyen mel t 0.127% BW (); rked mize t 0.415% BW plus soyen mel t 0.044% BW (); or pelleted soyen hulls t 0.415% BW plus soyen mel t 0.044% BW () (Tles 1 nd 2). Soyen mel ws inluded in oth nd diets so the supplemented diets would e isonitrogenous thus preventing the onfounding of protein nd energy effets of the supplements. Rie strw from smll squre les ws fed without hopping y offering weighed mount to eh niml t 0800 dily, fter feeding the tretment supplements. Wholeshelled mize ws rked with hmmer mill with the sreen removed in order to grind s ourse s possile within the restritions of equipment used. The resulting rked mize ontined vrious prtile sizes, from hlfkernel to flour size, somewht finer thn from roller mill. Soyen hulls, flky yprodut (170 kg/m 3 ) of soyen oil extrusion, re usully pelleted to inrese ulk density (513 kg/m 3 ) for trnsporttion nd storge nd to redue wste nd segregtion in feeding (omprison, rie rn = 320 kg/m 3 ). The soyen hull pellets of this study were typil for ommeril trde, mesuring pproximtely 5 mm dimeter y 15 mm long. Body weights were otined with no dietry restritions to determine quntity of supplement to e fed during eh period. To filitte diet dpttion (14 d), steers were housed together in pen with d liitum ess to rie strw. Tle 2. Steer ody weight (BW), diet omposition (% BW) nd estimted dietry energy (MJ/kg) nd protein (% DM) for different tretments Item Tretment diets 1 Diet formultion Rie strw (% BW) Ad liitum Ad liitum Ad liitum Ad liitum Soyen mel (% BW) Crked mize (% BW) Soyen hulls (% BW) Nutrient density of diet 2 Dietry NE m (MJ/kg) Dietry NE g (MJ/kg) Dietry CP (%) Tretment diets on DM sis: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with 2 Estimted using 1.3% BW intke of rie strw for ll tretments, DM sis.

3 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): During this time, steers were seprted dily nd individully fed their supplement. Minerl loks were offered free hoie only during diet dpttion ( % NCl with dded Zn, Fe, Mn, Cu, I, nd Co; Akzo Noel Slt, In., Clrks Summit, PA, USA). After diet dpttion, steers were pled into individul digestion stlls ( m), with seprte troughs nd utomti wterers, nd llowed three dys for limtion immeditely followed y five dys of dt olletion for in vivo digestion. While in the stlls, steers remined hltered nd tied, ut le to stnd or lie down t will. Totl fel olletions egn 17 d fter eing introdued to tretments (d 18). Apprent nutrient digestiility ws determined y weighing nd nlyzing dily DMI nd totl fel exretion from d 18 through 24. Rie strw nd supplements offered, nd rie strw refused (i.e., orts), were smpled dily from d 18 to d 23 nd omposited for eh steer nd smpling period. There were no supplement orts. Totl fel exretion ws weighed dily nd smpled, tking 5% liquot. Rumen environment Vrition in ruminl digestion due to supplementtion ws evluted from d 22 through d 24 y mesuring NH 3 -N, VFAs, ph, nd in situ dispperne. On d 22 ruminl fluid ws smpled t 0, 2, 4, 6, nd 8 h post-feeding of supplements eginning t Rumen fluid ws olleted y smpling ruminl ontents from four to five lotions within the rumen, whih ws pressed through four lyers of heeseloth. Colleted ruminl fluid ws immeditely pled on ie. After hilling, the ph ws determined using Thermo-Orion omintion eletrode meter (model 290A meter, Beverly, MA, USA). Ruminl fluid ws su-smpled (two replites of eh originl smple) nd entrifuged (900 g, 20 min). Superntnt ws trnsferred to plsti vils (sorted y dte, steer, nd h of olletion) ontining m-phosphori id (25% wt/vol) t 5 smple/1 id rtio. After mixing, vils were pled on ie until susequent ruminl fluid olletions were ompleted; smples were then frozen (-20 C) until VFA nd NH 3 -N nlysis. Upon VFA nlysis, frozen ruminl fluid ws thwed nd shken, nd 5 ml su-smples were entrifuged (30,000 g, 4 C, 20 min). To the resulting superntnt, 2-ethyl utyri id ws dded (2 g/l) followed y VFA nlysis using gs hromtogrphy equipped with mss spetrophotometer. Gs hromtogrphy nlysis ws sed on proedures desried y Grigsy et l. (1992) nd temperture grdient progrm desried y Btemn et l. (2002), who lso modified the proedure y using helium s the rrier gs with n injetion flow rte of 60 ml/min. Ammoni-N ws nlyzed using originl ruminl fluid smples (i.e., without 2-ethyl utyri id). Smples were thwed, vortexed, nd entrifuged (3,500 g, 4 C, 15 min) followed y nlysis using diret olorimetri method desried y MCullough (1967). Smples were inuted t 91% humidity, 5% CO 2, nd 37 C for t lest 35 minutes prior to olorimetri nlysis. Preliminry dt neessitted revising MCullough s (1967) method suh tht the smples were not deproteinted prior to NH 3 -N determintion. In situ study On d 22, 23, nd 24 in situ ruminl digestion ws evluted. For eh period, pooled smples of dily feed offered during the in vivo olletion were ground to pss 2-mm sreen. In situ smples onsisting of 3 g of ground rie strw, 5 g of soyen mel, 5 g of ground mize, or 5 g of soyen hulls were diretly weighed into seprte nylon in situ gs (No. 510; 5 m 10 m; 50±20 μm, Ankom, Firport, NY, USA). Eh steer reeived 12 in situ smples of rie strw nd 12 in situ smples of the supplement (soyen mel, mize or soyen hulls) ssigned to tht steer s diet (,, or, respetively). In situ smples for rie strw nd supplements were held in seprte mesh gs llowed to move freely within the rumen. At 0800, mesh gs ontining in situ smples were immersed in uket of wrm wter prior to plement in the rumen to dmpen smples nd filitte immedite miroil inoultion. At 2, 4, 6, 8, 16, nd 24 h fter initition, two in situ smples of rie strw nd two in situ smples of supplement were rndomly withdrwn from eh steer nd immeditely pled in ie wter to ese miroil digestion. All hrvested in situ smples were wshed y hnd ording to proedure desried y Vnznt et l. (1996). Dried gs were weighed, nd the remining smple ws nlyzed s desried elow. Lortory nlysis Rie strw, supplements, nd fel smples were ground in Thoms Wiley Mill (model 4, Thoms Sientifi, Swedesoro, NJ, USA) to pss through 2-mm sreen. Smples were nlyzed for DM, sh, CP, NDF, nd ADF (Vn Soest et l., 1991; AOAC 2003) using the Fier Anlyzer (ANKOM Tehnology, Firport, NY, USA). Anlysis for NDF inluded sodium sulfite to id in the removl of omplex proteins; in ddition α-mylse ws used. Neither NDF nor ADF were orreted for sh ontent. After ruminl inution, dried in situ gs with their remining smples were nlyzed for DM, NDF, nd ADF. Not enough feedstuffs remined in the in situ gs to nlyze for CP. In situ nutrient dispperne ws expressed s rtio of inuted to initil feed nutrient ontent. All lortory nlyses were onduted in duplite. Clultions nd sttistil nlysis Weights for rie strw, supplements nd fees were reorded to field sheets dily for eh steer. Weights nd

4 810 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): Tle 3. The effet of supplementing mize or soyen hulls on DM intke of steers onsuming rie strw during digestion tril Diets 1 SEM p-vlues Dry mtter intke Rie strw (kg/d) Totl (kg/d) Rie strw (% BW) Totl (% BW) Tretment diets on dry mtter sis: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with 2 Totl = Dry mter intke of rie strw plus supplement., Within rows, mens without ommon supersript differ (p<0.05). smple nlyses were entered nd tegorized y steer, tretment nd period on eletroni spredsheets for further lultions (lso y period, dy nd hour for ruminl nd in situ dt). From DMI nd fel exretion, pprent digestiilities were lulted s perent dispperne of DM, OM, NDF, ADF, hemiellulose (HC) nd CP. Hemiellulose ws lulted s differene etween NDF nd ADF residues. Response vriles were nlyzed s 4 4 Ltin squre, using the GLM proedure in SAS (V9.1, SAS Institute In., Cry, NC, USA). Plnned omprisons of vs. other tretments nd vs. nd were onduted using GLM CONTRAST sttements so proilities ould e reported. When signifint, mens were seprted using Ryn-Einot-Griel-Welsh multiplernge test (REGWQ) to minimize risk of Type 1 errors. Ruminl environment dt (NH 3 -N, ph nd VFAs) were nlyzed s 4 4 Ltin squre, where two smples were olleted from eh steer, using the GLM proedure for eh smpling time (0, 2, 4, 6 nd 8 h). The previous REGWQ proedure for men seprtions nd CONTRAST sttements were not used. Insted, lest-squres mens were seprted using multiple pirwise t-tests when tretment effets were signifint (p<0.05). In situ degrdtion rtios for DM, NDF nd ADF were nlyzed for eh smpling time (0, 2, 4, 6, 8, 16 nd 24 h) s 4 4 Ltin squre, using the MIXED proedure of SAS, where two smples were olleted from eh steer. All lortory nlyses were preformed in duplite. Steer nd time period were nylzed s fixed ftors; susmples nd su-susmples were nlyzed s rndom ftors. Lest-squres mens were reported for eh tretment y time for ruminl environment nd in situ degrdtion results nd were seprted using multiple pirwise t-tests when tretment effets were signifint (p<0.05). RESULTS AND DISCUSSION Digestion tril Rie strw in this study typified the low qulity reported y others. Most of the rie in the Mississippi delt re is grown in dry seeded ulture, where the permnent flood is not estlished until the five-lef stge. Coodrie, Cheniere, nd CL 161 re the most populr vrieties with verge yields out 5800 t/h (MSUres, 2007). Whether this strw is signifintly different from tht of other ountries is doutful when ompring the nutrient omposition of rie strw in Tle 1 with other pulished dt. High sh onentrtions (15.8%, Tle 1), grees with the 16.5 to 21.4%, reported y Gohl (1984) who indited sili ws the predominnt minerl present. With its high fier nd low CP (3.8%), rie strw lone oviously will not meet mintenne requirement of ruminnts. Consumption of rie strw nd other low qulity forges is often suppressed s shown in the present study (1.2 to 1.6% BW, Tle 3), whih is in greement with previous work (Sdulh et l., 1983; Preston nd Leng, 1984; Wnpt, 1990; Nguyen, 1996). The DMI of rie strw ws not ffeted y tretment (p = 0.34, Tle 3). As result, steers offered, or diets hd greter (p = 0.008) totl DMI ompred to steers not supplemented. However, dt indites tht supplements were not sustitutive of sl forge diet (Tle 3). Also, steers on the diet hd redued pprent digestion of DM, OM, nd CP ompred to those reeiving supplements (p<0.0001, Tle 4). Proly euse the diet hd smller quntity of tul supplement, pprent digestiility of NDF ws less ompred with nd diets (p = 0.004). Apprent DM digestiilities of nd were similr (p = 0.12) inditing tht soyen hulls nd rked mize hve similr feeding vlue for supplementing low qulity forges t the level of this study. Why soyen hulls, with more fier, n still hve similr digestiility to rked mize, with more strh, n e prtilly explined euse pprent NDF nd ADF digestiility ws greter (p<0.0008) for thn, nd there ws no differene in pprent HC digestiility (p = 0.43). Weidner nd Grnt (1994) reported tht non-forge fier soures, suh s soyen hulls, my inrese ruminl rte of pssge nd redue NDF digestiility due to smll prtile size nd greter speifi grvity. Grle et l. (1988) reported non-forge fier soures hve potentil to reple

5 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): Tle 4. The effet of supplementing mize or soyen hulls on pprent nutrient digestiility during digestiility tril Diets 1 SEM p-vlues Apprent nutrient digestiility (%) DM OM NDF ADF HC CP Tretment diets on dry mtter sis: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with 2 HC = Hemiellulose s differene etween ADF nd NDF.,, Within row, mens without ommon supersript differ (p<0.05). mg/dl NH 3 -N ph Smpling time (h) Smpling time (h) Figure 1. The effet of supplementing mize or soyen hulls on ruminl mmoni-n onentrtion (mg/dl) mesured 0 to 8 h fter feeding supplements. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p<0.0001), 2 h (p<0.0001), 4 h (p<0.01), 6 h (p<0.0001), nd 8 h (p<0.0001).,, Mens within smpling time differ, p<0.05. dietry forge, due to their low onentrtion of lignin nd euse they ontin lrge portion of digestile fier. Apprent CP digestiility ws lest for (10.9%), euse rie strw ontins very little protein (Tle 1) nd likely euse most of the CP in rie strw is ound in the ell wll mtrix (Cherney, 2000), mking it less ville to miroil fermenttion. Apprent CP digestiility ws gretest for followed y nd (p< , Tle 4). Ruminl hrteristis Compred to, supplementtion inresed (p<0.0001) ruminl NH 3 -N onentrtion pre- nd post-feeding with the exeption of prior to feeding (Figure 1). Diets nd hd similr nd gretest NH 3 -N onentrtion t 2 nd 4 h post-feeding (p = 0.63 nd 0.57, Figure 2. Chnge in ruminl ph from 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p = 0.26), 2 h (p = 0.46), 4 h (p = 0.17), 6 h (p = 0.13), nd 8 h (p<0.01).,, Mens within smpling time differ, p<0.05. respetively) ut were different pre-feeding nd 8 h postfeeding (p<0.04). Conentrtion of NH 3 -N for the diet mesured highest 2 h lter (4 h) nd ws intermedite etween nd the other two supplemented diets ( nd, Figure 1). Beuse not ll ruminl teri shre the sme N requirement, ruminl mmoni my e ffeted y miroil metolism of ville N (Hungte, 1966; Chlup et l., 1970; MAllen nd Smith, 1983). Ruminl mmoni lso depends on reyled mmoni nd, more importntly, on the extent of rohydrte fermenttion. In this study, mmoni vlues for supplemented nimls exeeded the optiml rnge (2 to 5 mg/dl) proposed y Stter nd Slyter (1974). As seen in Figure 2, ruminl ph of nd remined elevted nd reltively stle with mens rnging etween 6.9 nd 7.1 for nd etween 6.7 nd 6.8 for, nd were not different from eh other (p>0.08).

6 812 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): mm totl VFA Smpling time (h) mol/100 mol ette Smpling time (h) Figure 3. Totl voltile ftty id onentrtion (mm) of steers fed ermudgrss hy nd supplemented with mize or soyen hulls from 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with soyen hulls (0.415% BW) nd soyen mel (0.043% BW). Tretment time intertion. Mens within time differ: 0 h (p = 0.91), 2 h (p = 0.65), 4 h (p = 0.10), 6 h (p = 0.23), nd 8 h (p = 0.14). Prior to feeding, ruminl ph of remined numerilly more idi thn (6.7 vs. 7.1 ph, p = 0.07). Ruminl ph of oth nd remined similr (p = 0.13) t ll points mesured, delining to 6.42 nd 6.41 y 8 h, respetively. A similr study y Nguyen et l. (2007) reported greter hnge in ruminl ph, 8 h fter supplementing forge with rked mize (6.1) or pelleted soyen hulls (5.9) where soyen hulls were p<0.001 thn mize. Lk of differenes in the urrent tril might hve ourred euse rie strw diets with no supplement hd lower pprent DM digestiility (44.4%) thn the ermudgrss hy of Nguyen et l. (2007) (52.9%). On the other hnd, Pengkoum (1998) supplemented rie strw with ure treted ssv hips t 0.5% BW, nd ruminl ph rehed its lowest level of 6.1 (2 h) wheres our lowest level ws 6.4 for (6 h). Apprent DM digestiilty of Pengkoum s (1998) diet ws 58.8%, similr to 56.6% nd 60.0% for our nd diets, respetively. Fermenttion yproduts suh s VFAs nd lti id redily redue ruminl ph (Burrin nd Britton, 1986; Olson et l., 1999), nd reserh hs shown tht feeding soyen hulls prevented drsti redutions in ph providing ruminl environment more onduive to fier digestion (Klopfenstein nd Owen, 1987, Sung et l., 2007). In the present study neither mize nor soyen hulls redued ph elow norml physiologil rnge. However, feeding soyen hulls resulted in redution of ruminl ph equl to tht of mize. Shriver et l. (1986) reported tht ruminl ph of 5.8 ws hrterized y 43% redution in the Figure 4. Molr proportions of ette 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p = 0.05), 2 h (p = 0.09), 4 h (p = 0.12), 6 h (p<0.05), nd 8 h (p<0.05)., Mens within smpling time differ, p<0.05. proportion of miroes ssoited with fier prtiles, inditing fier digestion ws fvored in the present study. As seen in Figure 3, totl VFA onentrtion for steers onsuming remined reltively stle verging etween 149 nd 182 mm/l, whih ws numerilly less y ontrst ompring vs. other tretments ross ll times (p = ). Totl VFA onentrtions were not different mong tretments pre- nd post feeding (p>0.10), ut t 4 h post-feeding, produed numeril inrese, followed y derese in totl VFA onentrtion while oth nd exhiited numeril inrese from 6 to t lest 8 h post-feeding. Inresed totl VFA onentrtions immeditely followed peks of ruminl NH 3 -N (Figures 2 nd 3). Ammoni should inrese ph, ut didn t in this study (Figures 1 nd 2), inditing ville N is eing utilized y ruminl miroflor, onfirming the required synhrony etween N nd energy vilility. In ontrst, Nguyen et l. (2007), supplementing ermudgrss hy with mize nd soyen hulls showed tht the redution in ph oinided with the inrese in totl VFA onentrtions for the vrious feedstuffs. The present study showed similr reltionship etween totl VFA onentrtions nd ph, lthough not s pronouned. One exeption ourred when steers were supplemented with. For resons not yet understood, totl VFA onentrtions inresed while ruminl ph remined stle. In the urrent study, the pek totl VFA onentrtion ws 230 mm for 4 h post-feeding ompred to Nguyen et l. (2007) who reported 185 mm pek 6 h post-feeding

7 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): mol/100 mol propionte Smpling time (h) Figure 5. Molr proportions of propionte 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p = 0.32), 2 h (p = 0.50), 4 h (p = 0.62), 6 h (p = 0.40), nd 8 h (p = 0.20). Aette:propionte rtio Smpling time (h) Figure 6. Aette:Propionte rtio 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Re strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p = 0.25), 2 h (p = 0.40), 4 h (p = 0.61), 6 h (p = 0.27), nd 8 h (p = 0.12). for soyen hulls fed t 0.607% BW. It is possile tht peked t 4 h in the present study, s opposed to 6 h reported previously, euse there were fewer totl digestile nutrients ville from s shown y its redued digestiility of rie strw ompred with ermudgrss. Diurnl flututions in totl VFA onentrtions for steers onsuming highly firous mol/100 mol utyrte Smpling time (h) Figure 7. Molr proportions of utyrte 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p<0.05), 2 h (p<0.01), 4 h (p<0.05), 6 h (p = 0.11), nd 8 h (p = 0.09).,, Mens within smpling time differ, p<0.05. indite tht it ws redily digestile in the rumen even though (66.2% NDF nd 46.2% ADF; Tle 1). Previous reserh reported soyen hulls to e digested s muh s 75% in vivo (Streeter nd Horn, 1983; Hsu et l., 1987). Aette nd propionte re the two primry ftty ids produed in the rumen. Consumption of grins usully results in reltive inrese in molr proportions of propionte wheres fier inrese reltive proportions of ette. Supplementtion with soyen hulls hs shown mixed results with regrd to ruminl ette nd propionte onentrtions. Although soyen hulls ontin mostly fier nd very little strh, trils reported y Nguyen et l. (2007) nd Mrtin nd Hierd (1990) showed supplementtion with soyen hulls dereses molr proportions of ette nd inreses tht of propionte. In ontrst, this study showed no hnge (p = 0.2; Figure 5) in reltive proportions of propionte nd grees with Grigsy et l. (1992) who fed pproximtely 90% soyen hulls nd reported n inresed ruminl ette onentrtions nd redued ruminl propionte onentrtions. Figure 4 shows molr proportions of ette tended to e gretest for the diet 2 through 6 h post-feeding. By 8 h, ette ws gretest (p<0.05) for (Figure 4). Similrly, Gllowy et l. (1993) who found mize or soyen hulls to derese (p<0.06) the molr proportion of propionte. However, the ette:propionte rtio tended to derese during the present study wheres, Grigsy et l. (1992) reported ette:propionte rtios to inrese linerly when low qulity romegrss ws sustituted with 15, 30, 45, or

8 814 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): mol/100 mol vlerte Smpling time (h) Figure 8. Molr proportions of vlerte 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p<0.05), 2 h (p<0.001), 4 h (p<0.0001), 6 h (p<0.0001), 8 h (p<0.01)., Mens within smpling time differ, p< % soyen hulls. However, greement with these finding ws reported y Chse nd Hierd (1987) who found tht ntive grss hy supplemented with 0, 1, 2, or 3 kg ground mize to linerly derese the ette:propionte rtio. In ddition, these results re lso in greement with Mrtin nd Hierd (1990) reporting ette:propionte rtios to derese with inresing soyen hulls supplementtion. In the present study, the molr proportions of ette for ws not different (p<0.11) from or from 0 h to 8 h. However, molr proportion of ette for remined numerilly elevted (p<0.16) ove the other tretments from 0 to 8 h (Figure 4). Molr proportions of propionte remined reltively stle post-feeding (p<0.20), rnging from the lest of 16.7 mol/100 mol for t 0 h to the gretest of 18.7 mol/100 mol for t 8 h (Figure 5). The molr proportions of utyrte differed t 0, 2, nd 4 h with remining more onentrted thn nd ut not different from exept t 2 h (p<0.001). Butyrte ws similr mong tretments from 6 to 8 h postfeeding (Figure 7). Molr proportions of isoutyrte remined stle from 0 to 8 h for ll tretments, rnging etween 0.69 nd 1.00 mol/100 mol (dt not shown), nd showed no tretment differenes (p<0.11). Vlerte onentrtions were mrkedly ffeted y supplementtion from 0 to 8 h (p<0.05) ut,, nd did not differ (Figure 8). Isovlerte onentrtions followed similr trend to vlerte exept tht ws ssoited with less proportions of isovlerte thn t 2 h nd mol/100 mol isovlerte Smpling time (h) Figure 9. Molr proportions of isovlerte 0 to 8 h fter feeding supplements to steers onsuming rie strw. Tretment diets: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with Tretment time intertion. Mens within time differ: 0 h (p<0.05), 2 h (p<0.05), 4 h (p<0.05), 6 h (p = 0.11), 8 h (p = 0.11).,, Mens within smpling time differ, p<0.05. ws not different from or other supplements t 4 h (Figure 9). In situ dispperne of nutrients In situ dispperne of rie strw DM from the rumen (Tle 5) ws gretest for the tretment 6 to 24 h postfeeding (p<0.04). Rie strw NDF nd ADF dispperne tended to e gretest for supplemented steers (16 to 24 h, p<0.02). Redution in rie strw dispperne in diet is likely due to n insuffiient supply of metolizle protein within the rie strw (Tles 1 nd 2) euse did not inlude soyen mel. The ruminl DM dispperne of rked mize in the diet ws greter (p<0.05) thn soyen hulls in the diet from 2 to 8 h fter feeding supplements. At 24 h, ruminl soyen hull dispperne exeeded (p<0.05) tht of mize, likely euse muh of the mize strh would hve een digested or wshed out of the smple gs. Although soyen hulls were digested slower thn mize, they still proved to e highly digestile, whih is supported y previous studies evluting the digestion of soyen hulls y ttle (Quike et l., 1959; Hintz et l., 1964; Ludden et l., 1995). Compring nd, the differenes in pprent fier (NDF nd ADF) digestiilities shown in Tle 4 n e explined y in situ disppernes of rie strw nd supplements in Tle 5 nd 6. By implition, the fier digestion of in Tle 4 involved fier from oth rie strw nd soyen hulls. Beuse there were no differenes in in situ fier (NDF nd ADF) dispperne

9 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): Tle 5. Lest squres mens of ruminl remined rtios of inuted to initil rie strw nutrient ontent etween supplemented nd non-supplemented steers Inution (h) Tretment 1 SEM p-vlue DM < < NDF < ADF Tretment diets on dry mtter sis: = Rie strw diet with no supplement; = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with 2 Proility of effets due to tretment within eh time.,, Within row, mens without ommon supersript differ (p<0.05). Tle 6. Lest squres mens of ruminl remined rtios of inuted to initil nutrients from soyen mel, mize, nd soyen hulls in respetive supplemented steers Inution (h) Supplement y tretment 1 Soyen mel Mize Soyen hulls SEM p-vlue DM < < < < < < < NDF ADF Tretment diets on dry mtter sis: = Rie strw diet supplemented with soyen mel (0.127% BW); = Rie strw diet supplemented with mize (0.415% BW) nd soyen mel (0.044% BW); = Rie strw diet supplemented with soyen hulls (0.415% BW) nd soyen mel (0.043% BW). 2 Proility of effets due to tretment within eh time.,, Within row, mens without ommon supersript differ (p<0.05).

10 816 Nguyen et l. (2008) Asin-Aust. J. Anim. Si. 21(6): from the rie strw (Tle 5), then the differenes etween nd in pprent totl trt digestiilities me from the supplements (mize nd soyen hulls, respetively). This seems in onflit with Tle 6 whih shows more rpid dispperne of NDF nd ADF for mize thn for soyen hulls. However, the initil onentrtion of these fier omponents ws muh less to egin with (Tle 1). Dispperne rtios greter thn 1 in Tle 5 nd 6 re most likely explined y prtil espe of smple mteril from in situ gs. Current in situ findings differ from similr study of Nguyen et l. (2007) who reported differene in ADF in situ dispperne of ermudgrss hy. They suggested tht supplying firous feedstuff to the rumen would promote fier-digesting teri while suppressing strh teri. They lso suggested tht feeding t lest 0.5% of BW of soyen hulls n enhne forge digestion through dditive nd ssoitive effets resulting in more effiient supplement thn mize. Current dt does not onur with these findings likely do to the differenes in forge qulity nd digestiility etween ermudgrss nd rie strw. In summry, steers were fed diets of rie strw d liitum supplemented with mize or soyen hulls t 0.4% BW to provide pproximtely 4 MJ NE m per kg of diet. Rie strw DMI ws not ffeted y supplementtion, inditing no sustitutive effets. In ddition, mize or soyen hulls enhned digestiility of the fier in rie strw when protein requirements were met with soyen mel. In spite of high fier ontent of soyen hulls, this study suggests tht they re s effiient s mize for supplementing rie strw primrily euse fier in soyen hulls re highly digestile s shown y in vivo digestiility nd in situ dispperne. Our understnding of the ssoitive effets of soyen hulls, when supplementing low qulity forges suh s ermudgrss, hs eome lerer in reent yers. Rie rn should perform similrly to soyen hulls (Orden et l., 2000; Chudhry et l., 2001). This study shows tht rie strw, even with its lower protein nd higher sili ontent, hs similr ssoitive effets, when dditionl protein is lso provided, euse fier digestion is similr. When feeding ttle rie strw diets, energy nd protein-sed supplements re essentil, ut highly digestile fier-sed supplements my tend to inrese rie strw utiliztion. REFERENCES AOAC Offiil Methods of Anlysis. 17th Ed. Assoition of Offiil Anlytil Chemists. Arlington, Virgini. Btemn, H. G., II, C. C. Willims nd Y. H. Chung Effets of supplementl zin in high qulity diets on ruminl fermenttion nd degrdtion of ure in vitro nd in vivo. Prof. Anim. Si. 18: Burrin, D. G. nd R. A. Britton Response to monensin in ttle during suute idosis. J. Anim. Si. 63: Chlup, W., J. Clrk, P. Opliger nd R. Lvker Ammoni metolism in ruminl teri nd muos from sheep fed soy protein or ure. J. Nutr. 100(2): Chse, C. C., Jr. nd C. A. Hierd Utiliztion of low qulity ntive grss hy y eef ows fed inresing quntities of orn grin. J. Anim. Si. 65: Chudhry, L. C., A. Shoo, Neet Agrwl, D. N. Kmr nd N. N. Pthk Effet of repling grin with deoiled rie rn nd molsses from the diet of ltting ows. Asin-Aust. J. Anim. Si. 14: Cherney, D. J. R Chrteristis of forge y hemil nlysis. In: Forge evlution in ruminnt nutrition. (Ed. D. I. Givens, E. Owen, R. F. E. Axford nd H. M. Omed). CABI Pulishing, Oxfordshire, United Kingdom. p Chowdhury, S. A Effet of grded levels of ottonseed ke supplementtion on intke, nutrient digestiility, miroil N yield of growing ntive (Bos indius) ulls fed rie strw. Asin-Aust. J. Anim. Si. 14: Elseed, A. M., A. Fdel, J. Sekine, M. Hishinum nd K. Hmn Effets of mmoni, ure plus lium hydroxide nd niml urine tretments on hemil omposition nd in so degrdility of rie strw. Asin-Aust. J. Anim. Si. 16: Gohl, Bo Tropil Feeds. FAO Animl Prodution nd Helth Series 12. Rome, Itly. Gllowy, D. L., Sr., A. L. Goetsh, L. A. Forster, Jr., A. R. Ptil, W. Sun nd Z. B. 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