J. L. Firkins, L. L. Berger, N. R. Merchen and G. C. Fahey, Jr. University of Illinois 1'2 Urbana ABSTRACT

Transcription

1 EFFECTS OF FORAGE PARTICLE SIE, LEVEL OF FEED INTAKE AND SUPPLEMENTAL PROTEIN DEGRADABILITY ON MICROBIAL PROTEIN SYNTHESIS AND SITE OF NUTRIENT DIGESTION IN STEERS J. L. Firkins, L. L. Berger, N. R. Merchen and G. C. Fahey, Jr. University f Illinis 1'2 Urbana 6181 ABSTRACT A 2 s factrial arrangement f treatments was used t study main effects and interactins between particle sie f prairie hay (chpped vs grund), tw levels f feed intake (6 and 9% f ad libitum) and ruminal degradability f prtein surces [dry crn gluten feed (DCGF) vs dry distillers grains (DDG)] n ruminal and ttal tract digestin in eight ruminai- and dudenalcannulated steers. Steers were fed every 2 h t apprach steady-state feeding cnditins. Steers fed grund hay diets digested higher (P.5) percentages f ttal digestible rganic matter (OM) and neutral detergent fiber (NDF) in the rumen and had lwer (P.5) nnammnia-nnbaeterial N (NANBN) flws t the dudenum than did thse fed chpped hay, prbably because greater surface area f grund hay allwed mre extensive ruminal fermentatin. Prtein surce intake interactins were nted fr ruminai OM and NDF digestin when expressed as percentages f ttal digestin. At lw intakes, steers fed DCGF had higher (P.O5) percentages f ttal digestible OM and NDF disappearing in the rumen than did thse fed DDG. Steers fed DCGF had lwer ttal N, NANBN and ttal amin acid (AA) flws at the dudenum than did thse fed DDG, indicating that less DCGF prtein escaped ruminal degradatin. Steers fed DDG had greater (P.O5) ttal tract NDF digestin, suggesting that escape prtein frm DDG may stimulate hindgut fermentatin and thereby affect site and extent f nutrient digestin. Regressin analysis indicated that extent f ruminal fermentatin and efficiency f micrbial grwth in viv are assciated with ruminal rates f passage within individual animals. When steers were fed at high-intake levels (1.6% f bdy weight), ruminal dilutin rates were nt increased (P.5) due t frage particle sie r level f intake treatments, accunting, in part, fr the lack f expected treatment differences in efficiency f bacterial grwth and dudenal N flw, and fr the lw number f interactins between main effects. (Key Wrds: Particle Sie, Feed Intake, Prtein Degradatin, Steers.) Intrductin Replacement f urea with amin acids r casein may increase efficiency f micrbial crude prtein (MCP) synthesis in the rumen (Bergen et al., 1982). Hwever, little is knwn cncerning the effect f inclusin f slwly degradable prtein surces in ruminant diets n efficiency f bacterial grwth. Prtein requirements are greatest fr the grwing calf r lamb during stages f grwth when frages cmprise a relatively high prprtin f the diet. Tw imprtant factrs affecting ruminal digestin f frages are particle sie and level f 1 Dept. f Anita. Sci. 2 Research supprted in part by a grant frm Crn Refiners Assc., Inc., Washingtn, DC. Received May 2, Accepted Nvember 14, feed intake. Grinding frages generally decreases ruminal fluid-phase dilutin rate (D) but increases particulate D (Westn and Hgan, 1967) and decreases extent f ruminal digestin (Blaxter et al., 1956 ; Hgan and Westn, 1967). Increasing feed intake als results in faster D (Grvum and Williams, 1977). Increasing D f particulate r fluid digesta may increase efficiency f MCP synthesis (Bergen et al., 1982). Cnsequently, particle sie and level f feed intake may als affect efficiency f ruminal MCP prductin. Studies evaluating effects f level f feed intake and frage prcessing in the same experiment (Beever et al., 1972; Alwash and Thmas, 1974) have shwn depressins in ruminal digestin f rganic matter (OM) and fiber due t decreased ruminal retentin times assciated with greater feed intakes r smaller frage particle sie. Hwever, pssible interactins f these factrs n ruminal digestin have nt been elucidated. 181 J. Anim. Sci :

2 182 FIRKINS ET AL. It is uncertain hw inclusin f prtein surces that vary in ruminal degradability affects digestin f frages under these cnditins. The bjectives f the current study were t determine main effects and interactins f frage particle sie, prtein surce N degradability and level f feed intake n ruminal and ttal tract digestin in steers. Materials and Methds Ruminal and ttal tract digestin f experimental diets were determined using fur Herefrd (35 kg) and fur Angus-Herefrd (55 kg) steers fitted with cannulae in the rumen and prximal dudenum. Steers were blcked by weight grup and randmly alltted t ne f eight cmbinatins f three dietary factrs fr each f fur perids, with restrictins that n animal received the same treatment twice and that treatment cmbinatins remained balanced between blcks after fur perids (tw bservatins f each treatment cmbinatin per blck). A randmied incmplete-blck design with a 23 factrial arrangement f treatments was used. Mdel sums f squares were partitined int single degree f freedm (df) cmparisns fr three main effects and fur interactins. Data als were blcked by perid (3 df) and animal nested within weight grup (6 dr). Three thusand kilgrams f baled prairie grass hay were ammniated {3 g ammnia (NH3)/kg dry matter (DM)] in a sil press bag fr 2 wk. Prairie hay was chsen because f its lw crude prtein cntent (5% n a DM basis). It was ammniated t increase DM digestibility and nn-prtein N cntent t allw adequate ruminal NH 3 cncentratins fr ptimal micrbial grwth. Because ammniated hay cntained 15.5% crude prtein, nn-ammniated prairie hay als was incrprated int the diets t decrease N cntent. Ammniated and nn-ammniated hay were either grund thrugh a hammer mill (1-cm screen) r chpped with a frage chpper (5.8-cm screen). Prtein surces cmprised 2% f diet DM and remaining ingredients were included t balance diets t cntain 15% crude prtein (table 1). Particle sie f grund and chpped frages was determined using a dry-sieving technique (Wald et al., 1971). Because grund hays, bth ammniated and nn-ammniated, lst apprximately.9 percentage units f crude prtein during grinding, ammniated hay cmprised a higher percentage f the grundthan f the chpped-hay diets. Dry crn gluten feed (DCGF) and dry distillers gains (DDG) were chsen as prtein surces because they have a similar amin acid cmpsitin (Annymus, 1975, 1981) but DCGF-N is mre rapidly degraded in the rumen than is that f DDG (Firkins et al., 1984). Casein, which has a different amin acid pattern but is very rapidly degraded in the tureen, was added t DCGF diets t make prtein supplements isnitrgenus. A cracked crn-based supplement was fed t prvide supplemental minerals and vitamins. Samples f all feeds were taken daily 2 d befre and during each cllectin perid and cmpsited fr nutrient analysis. Diets were fed in equal prtins every 2 h using autmatic feeders (Stkes et al., 1979) t establish apprximate steady-state cnditins in the gastrintestinal tract. Diets were fed at 9 r 6% f ad libitum intake f the lwest-cnsuming steers in each weight grup (8.2 vs 5.4 and 6.4 vs 4.2 kg DM intake/d fr high- vs lw-intake treatments fr the heavier and lighter steers, respectively). Steers were allwed 1 d dietary adaptatin at the beginning f each experimental perid. Cbalt ethylenediaminetetraacetate (C-EDTA) was prepared (Uden et al., 198) and mixed (.56 g C) with the diet daily fr use as the dudenal fluid-phase flw marker. Chrmic xide (Cr 23) was used as the particulate-phase marker (.15% f diet DM). On d 11 t 15 f each perid, dudenal samples (35 ml fr the heavier steers and 3 ml fr the lighter steers) were cllected every 6 h and cmpsited. On each successive day, cllectin started 7 min later s that 2 samples were btained arund a 24-h time perid. Fecal grab samples (2 g) were taken twice daily such that a sample was btained fr every 14-rain interval f a 24-h time perid (1 samples). Feeding f C-EDTA and Cr 23 was discntinued n d 16. On d 18, ytterbium chlride (YbC13" 6H2 O) was disslved in distilled water and sprayed n 1/13 prtins f the diets (1 g Yb). After these prtins were cnsumed as a single meal, 167 ml C-EDTA slutin (.95 g C) was pulsedsed via the ruminal cannulae. Immediately befre pulse-dsing f passage rate markers and at 4, 8, 12, 24, 3 and 36 h pst-dsing, ruminal samples (4 ml) were taken with a cre sampler. A.75-m cnduit pipe (3.5-cm id), which had a wire inserted inside and cnnected t a stpper at the bttm, was inserted

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4 184 FIRKINS ET AL. thrugh the ruminal fistula. The stpper was remved, the pipe pushed thrugh the digesta t the bttm f the rumen and the bttm plugged with the stpper. This technique enabled a representative "cre" sample f ruminal cntents t be btained. Additinal ruminal cntents (5 ml) were taken at the -, 3- and 36-h sampling times and squeeed thrugh tw layers f cheeseclth. Fifty milliliters ruminal fluid frm these samples were acidified with 3 ml 6 N HC1, cmpsited and centrifuged at 27, x g fr determinatin f ruminal NH 3 (Chancy and Marbach, 1962) and vlatile fatty acid (VFA) cncentratins (Erwin et al., 1961). A Varian ~ Mdel 46 autmated gas chrmatgraph equipped with a hydrgen flame iniatin detectr was used t quantify VFA. It hused a stainless steel clumn (18 cm lng 3mm d) packed with Chrmsrb W (6 t 8 mesh) cated with 2% Tween 8 and 2% phsphric acid. Helium was used as a carrier gas with a flw rate f 4 ml/min. The ven temperature was 125 C. The remaining ruminal fluid was cmpsited by animal and centrifuged at 5 g and 27, x g fr islatin f bacteria-rich fractins as described by Firkins et al. (1984). The bacterial islates were freee-dried and analyed fr N (AOAC, 1975) and nucleic acid cntent (inn and Owens, 1982). Ttal dudenal cntents were centrifuged at 5 g t separate fluid frm particulate matter. While dudenal fluid was being cntinuusly stirred with a hmgenier, subsamples were taken fr determinatin f N, NH3 (Chaney and Marbach, 1962) and C (Uden et al., 198) cntents. Als, ten milliliters were taken, freee-dried and analyed fr nucleic acid cntent (inn and Owens, 1982) and 1 ml were dried at 9 C and analyed fr Cr2 3 (Williams et al., 1962). This allwed crrectin fr Cr23 flwing with the fluid phase, the flw f which was quantified using C-EDTA as the reference marker. Dudenal particulate matter and fecal samples were dried at 6 C in a frced-air drying cabinet and grund in a Wiley mill (2-mm screen). Feed, dudenal particulate matter and fecal samples were analyed fr DM, Kjeldahl N and OM (AOAC, 1975) and fr neutral detergent 3 Varian, Inc., Walnut Creek, CA. 4 Beckman Instruments, Pal Alt, CA. fiber (NDF; Gering and Van Sest, 197). Cracked crn supplement and dudenal and fecal samples were analyed fr Cr2 3 (Williams et al., 1962). Nucleic acid cntent (inn and Owens, 1982) f dudenal particulate matter was determined. Cmpsite feed samples, dudenal particulate matter, bacterial islates (.15 g each) and dudenal fluid (1 ml, freee-dried) were hydrlyed fr amin acid analysis with 15 ml 6 N HC1 (previusly bubbled with N 2 fr 15 rain) at 11 C fr 22 h in sealed test tubes evacuated with N2. Hydrlysates were millipre-filtered and adjusted t ph 2.2 with citrate buffer cntaining NaOH. Amin acid cncentratins were determined n a Beckman 4 63 amin acid analyer. Ruminal cntents were squeeed thrugh eight layers f cheeseclth. The particulate matter was dried (6 C), grund (2-mm screen)and analyed fr Yb by atmic absrptin spectrphtmetry as described by Firkins et al. (1984). Fluid was analyed fr C (Uden et al., 198). Ruminal particulate and fluid D were calculated as the slpe f the regressin f the natural lgarithm f Yb and C cncentratins, respectively, ver time. The antilgarithm f the y-intercept f C regressin was divided int the amunt f C pulse-dsed fr calculatins f rumen fluid vlume. All flw calculatins were based n Cr23:g DM r C:ml liquid ratis, as described by Faichney (1975). Statistical analyses were perfrmed using analysis f variance btained frm the General Linear Mdels prcedure, and Pearsn crrelatin cefficients frm the Crrelatin prcedure (SAS, 1982). Means were cmpared using the F test-prtected, Least Significant Difference methd (Carmer and Swansn, 1973). Results and Discussin Essentially n chrmic xide was present in fluid fractins f dudenal samples. Chrmic xide des nt assciate exclusively with either particulate- r fluid-phase digesta (Ellis et al., 1982) but flws predminantly with the particulate phase (MacRae and Armstrng, 1969). Our methd f separating dudenal particulates frm fluid (centrifuging at 5 x g) may have separated small particles and Cr2 3, which rdinarily flw with the fluid phase, int the particulate fractin. Hwever, such an errr shuld be distributed evenly acrss treatments. Therefre, dudenal particulate

5 PARTICLE SIE, INTAKE AND PROTEIN SOURCE IN STEERS 185 flw was based n Cr2s cntent withut crrecting fr Cr2a in the fluid phase. In rder t maintain isnitrgenus diets while using the same percentage f ammniated ~ and nn-ammniated hays (table 1), it wuld have been necessary t add urea t grund hay diets rather than varying levels f hay. Because grund hays cntained less N, it is likely that mre leaf tissue was lst during prcessing than ccurred with chpped hays. Other researchers have nted lwer N cntent due t frage prcessing, attributing this t lss f leaves (Beever et al., 1981 ;Jaster and Murphy, 1983). Frage stems are less digestible than are leaves (Lared and Minsn, 1975) s the relative ~- digestibility f grund hay wuld prbably be u, slightly lwer than wuld that f chpped hay given similar retentin times in the tureen.,.~ When ammniated r nn-ammniated hay ~. (grund t pass a 2-mm screen) were incubated m in situ int the same fur steers, 35.2 and 56.]% f the riginal DM, respectively, remained after 27 h f mminal expsure. This,~ wuld suggest that there wuld be apprximately a 21% difference in ruminal hay DM a: digestibility due t ammniatin. Theretically, this wuld result in a 1.5% (21% 7% difference in ammniated hay level in the diet) greater ruminal DM digestibility f grund vs chpped hay diets. The prbable lwer di- gestibility f grund hays due t greater leaf lss shuld have been ffset by the 7 percent- ~) age unit higher level f ammniated hay in the a: K) diet, and the latter effect shuld nt have significantly biased results due t hay prcessing. Lack f treatment differences in ttal tract OM r NDF digestin supprt this hypthesis. N differences (P>.5) due t treatment were nted fr particulate- r fluid-phase ruminal D (table 2). Level f intake had relatively less effect n ruminal passage rates in this study than in previus reprts (Grvum and Williams, 1977;Mudgal et al., 1982; Staples et al., 1984). On average, steers fed at high intakes were fed at abut 1.6% f bdy weight but intakes greater than 1.75% f bdy weight may be necessary t elicit respnses in ruminal D due t feed intake (F. N. Owens and A. L. Getseh, persnal cmmunicatin). Higher intake levels als may be required fr differences in ruminal D t ccur due t frage prcessing. Dudenal fluid flw and ruminal fluid vlume were greater (P.5) fr steers receiving diets at high vs lw levels f intake, ~' ~_ E O~ 9 -a "-a ~ "-a --a E. 6 v II d 6 E 8 e~

6 186 FIRKINS ET AL. prbably due t greater saliva prductin and water cnsumptin. The higher (P.5) ruminal NH 3 cncentratin bserved fr steers fed DCGF than fr thse fed DDG reflects the faster degradability f DCGF prtein. Ttal VFA cncentratins tended (P.1) t be higher fr steers fed at high intakes. A linear increase in VFA cncentratins with increased intake was reprted by Staples et al. (1984), prbably due t increased quantity f substrste available fr fermentatin. Treatment differences in mlar prprtins acetate and butyrate, while statistically significant, are lw in magnitude and may be bilgically insignificant. Prcessing f hay had n effect n mlar prprtins f individual VFA in the current study. Osburn et al. (1976) nted that grinding frages resulted in a decreased mlar rati acetate:prpinate. Hwever, the acetate:prpinate rati was increased with mre frequent feeding (Kaufmann et al., 198; Getsch and Galyean, 1983). The frequent feeding pattern used in this study may have caused the lack f respnse in mlar prprtins f VFA, which wuld be anticipated due t hay prcessing by animals given ad libitum access t feed. Organic matter intake and dudenal OM flw were nt affected (P>.5) by prcessing methd (table 3). Apparent ruminal OM digestin and percentage f digestible OM disappearing in the rumen were greater (P.5) fr steers fed grund- vs chpped-hay diets. Because n differences were nted fr ruminal particulate D (table 2) and because f the frequent feeding pattern used, bth grund and chpped hay particles were prbably retained in the rumen fr the same length f time. Therefre, greater surface area per gram DM f grund hay shuld allw mre rapid clniatin by ruminal micrbes and, subsequently, mre extensive fermentatin f grund vs chpped hay. Crrecting ttal dudenal OM flw fr bacterial OM did nt change relatinships fr any main effects (data nt shwn). Greater NDF intakes (P.5) by steers fed chpped-hay diets ccurred due t slightly greater DM intakes and slightly greater NDF cncentratins in chpped hay (66.8, 68.9, 73.8 and 74.3% NDF fr ammniated-grund, ammniated-chpped, grund and chpped hays, respectively). Steers fed grund-hay diets had lwer (P.5) dudenal NDF flw and higher (P.5) ruminal NDF digestibilities than did thse fed chpped hay (% intake and % ttal NDF digestin). As stated previusly, this is prbably due t greater surface area f grund vs chpped hay. Because prairie hay cntained 67 t 74% NDF, mre extensive ruminal NDF digestin accunts fr mst f the increase in ruminal OM digestin in steers fed grund- vs chpped-hay diets. Increased pstruminal digestin f cell walls due t smaller frage particle sie has been reprted (Beever et al., 1972, 1981; Thmsn et al., 1972). These effects are prbably due t decreased ruminal retentin times (Hgan and Westn, 1967) and cnsequent escape f digestible cell wall material t the lwer tract. Lack f differences in D due t hay prcessing in the current study explains why n shift in site f NDF digestin t the lwer tract was bserved with chpped vs grund treatments. Organic matter intake, OM flw, NDF intake and NDF flw t the dudenum were greater (P.5) fr the high vs lw level intake (table 3). Apparent ruminal NDF digestir/, expressed as a percentage f intake r as a percentage f digestible NDF, was lwer fr steers fed high vs lw levels f intake. Because significant prtein surce intake interactins were detected, these results will be discussed later. Organic matter intake was nt different (P>.5) but OM flw t the dudenum was lwer (P.5) fr steers fed DCGF vs DDG (table 3). Apparent ruminal OM digestibility was higher (P.5) fr steers fed DCGF- than fr thse fed DDG- cntaining diets. Greater intake f NDF by steers fed DDG diets than by thse fed DCGF diets was due t a slightly higher NDF cntent f DDG relative t DCGF (45 and 4% f DM, respectively). N difference due t prtein surce was nted fr percentage ruminal NDF digestin (% NDF intake). Hwever, steers fed DDG diets had greater (P.5) ttal NDF digestibilities and lwer percentages f ttal NDF digestin ccurring befre the dudenum than did thse fed DCGF diets. These results will als be discussed later. Dudenal NH3-N flw (table 4)was higher (P.5) fr steers fed grund- vs chpped-hay diets, prbably due t a greater amunt f NH 3 arising frm a greater percentage f ammniated hay in these diets. Feeding grund frages generally results in increased dudenal N r amin acid flws cmpared with feeding chpped frages (Osburn et al., 1976; Beever et al., 1981). Hwever, this was nt bserved in the current trial, prbably because the

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8 logg FIRKINS ET AL. e~ ~a ua~ r, e~ m ~8 ~ _ a2 m ~ 8~ ~ r~ ~ua:..i1 II M [- ~ g e ~.._. m -'-a'-a ~ -'-a ~ -,~, "D "~ "I~ ~" "~I ~ ~'

9 PARTICLE SIE, INTAKE AND PROTEIN SOURCE IN STEERS 189 twelve times daily feeding frequency negated expected differences in ruminal particulatephase D. In fact, chpped-hay treatments had higher NANBN flws t the dudenum, prbably due t lwer ruminal OM digestin f this treatment and less digestin f frage prtein in chpped hay. Steers fed high vs lw level f intake had greater (P.5) flws f dudenal particulatephase N, fluid-phase N and NH3-N, (table 4). When expressed as percentages f N intake, level f DM intake had n effect n dudenal NANBN r N flws r ttal N digestin. Increased DM intake has resulted in increased quantity f feed prtein escaping ruminal digestin (Miller, 1973; Tamminga, 1979), prbably because f faster passage f ruminal particulate matter. Passage rate differences were nt detected in ur study, explaining lack f treatment differences in prprtins f dietary N escaping the rumen due t level f intake. Bacterial N:nucleic acid ratis were affected (P.5) by weight grup and perid (data nt shwn), s individual ratis btained frm each steer were used t calculate bacterial N flws. The ~ average N:nucleic acid rati in bacterial islates was Micrbial OM flws were subtracted frm ttal dudenal OM flws t calculate efficiency f micrbial grwth n a truly digested OM basis. Dudenal flws f bacterial N in bth fluid and particulate matter were greater (P.5) fr steers fed high vs lw level f intake (data nt shwn). Althugh ttal bacterial crude prtein flw was greater (P.5) in steers fed at high intakes, efficiency f bacterial grwth was nt affected (P>.5) by level f intake. Steers fed DDG, cmpared with thse fed DCGF, had greater (P.5) dudenal particulate-phase N flw, lwer (P.5) NH3-N flw and greater (P.5) NANBN and ttal N flws t the dudenum (table 4). Assuming that casein additin (2.8% f diet DM) had a small effect, this crrbrates previus wrk (Firkins et al., 1984) which shws that N f DDG escapes ruminal fermentatin t a greater extent than des N f DCGF. Decreased dudenal N flw in steers fed DCGF prbably resulted frm increased ruminal degradability f DCGF vs DDG and, subsequently, greater NH 3 absrptin acrss the ruminal wail. Because dudenal flw f bacterial crude prtein was similar between steers fed DDG r DCGF, the trend (P.6) fr greater bacterial efficiency nted fr the DDG treatment reflects the lwer true ruminal digestin f the DDG diets. Intake and flw f amin acids (AA) t the dudenum are presented in table 5. Amunt f bacteria/ and dudenal AA flwing with fluid and particulate phases f digesta were calculated independently and then pled. N differences (P>.5) in intake, bacterial flw r ttal dudenal flw f essential, nnessential r ttal AA (EAA, NAA and TAA, respectively) were detected due t hay prcessing. Greater DM intakes by steers fed the high level f intake resulted in greater bacterial and ttal dudenal AA flws cmpared with thse fed the lw level f intake. Level f intake had n effect n bacterial and dudenal TAA flw, hwever, when expressed as percentages f TAA intake. These data crrbrate the earlier cnclusin that level f intake had n effect n NANBN flwing t the dudenum. Steers fed DDG, cmpared with thse fed DCGF, had greater (P.5) intakes f NAA and TAA (table 5). Steers fed DDG had greater (P.1) dudenal flws f EAA, NAA and TAA than did thse fed DCGF diets. Because dietary treatment had n effect n bacterial AA flw r dudenal fluid-phase AA flw (data nt shwn), these data verify the greater ruminal escape f DDG vs DCGF AA. ThrenJne, glycine and lysine flw were the nly values nt affected (P>.5) by prtein surce, mst likely due t the high cncentratins f these AA in bacterial prtein. Flws f threnine and glycine were similar t their intakes (data nt shwn) but bacterial flw f lysine was greater than dietary intake (37.1 and 35.9 g/d bacterial flw vs 24.9 and 17.6 g/d dietary intake f lysine frm DCGF and DDG treatments, respectively). The greater lysine intake f DCGF treatments is due t additin f casein t these diets. Cncentratins f individual AA in islated bacteria (data nt shwn) were nt affected (P>.5) by treatment and were very similar t thse reprted by Bergen et al. (1968). Bacterial prtein als had similar cncentratins f ttal EAA cmpared with ttal NAA, whereas diets used in this study had abut 2% higher cncentratins f ttal NAA than ttal EAA. Ttal AA flw t the dudenum was abut 32% greater than TAA intake acrss treatments. Thus, ruminal micrbes utilied cnsiderable amunts f dietary r recycled nn-prtein N fr amin acid bisynthesis and imprved the

10 19 FIRKINS ET AL. TABLE 5. INTAKE AND DUODENAL FLOW OF AMINO ACIDS IN STEERS FED CHOPPED OR GROUND HAY" AT TWO LEVELS OF INTAKE WITH TWO PROTEIN SOURCES Item Prcessing methd Intake Prtein surce a Chpped Grund High Lw DCGF DDG SE b Intake, I~/d EAA c 226 NAA clef 278 TAAdfg 55 Bacterial flw t dudenum, g/d EAA d 216 NAA d 223 TAA d 439 Ttal dudenal flw, g/d EAA df 357 NAA df 44 TAA df adcgf -- dry crn gluten feed; DDG = dry distillers grains. bstandard errr f the mean. CEssential amin acids including arg, his, ile, leu, lys, met, phe, thr, val. dlntake effect (P.5), ennessential amin acids included ala, asp, gin, gly, pr, ser, tyr. fprtein surce effect (P.5). gttal amin acids included EAA + NAA. quality (EAA:NAA) f prtein reaching the dudenum. Prtein surce x intake interactins (P.5; table 6) were detected fr apparent ruminal OM digestin (% OM intake) and OM and NDF digestin in the rumen (% ttal OM r NDF digestin). At lwer intakes, a trend (P.ll) fr greater ruminal OM digestin and higher (P.5) prprtins f the ttal OM and NDF digestin f DCGF diets ccurred in the rumen than at higher intakes. This effect was nt detected when DDG diets were fed. Firkins et al. (1985) shwed that NDF disappearance frm dacrn bags was greater fr DDG than fr DCGF at 9- and 18-h ruminal expsure. Firkins et al. (1984) nted that ruminal NDF digestibility tended t be lwer fr DCGF than fr DDG diets. Because DCGF and DDG bth cntain mst f the riginal fiber frm crn grain (Annymus, 1975, 1981), nly differences in prcessing shuld affect fiber digestibility in these feeds. Acid treatment during wet-milling (Annymus, 1975) may have hydrlyed sme f the DCGF hemicellulse, resulting in a residual NDF fractin that was mre resistant t micrbial fermentatin than was DDG fiber. Cnsidering that ruminal NDF digestibility was unaffected due t prtein surce in this study, alng with abve evidence that suggests that NDF f DCGF is ften less digestible in the rumen than is that f DDG, it may be hypthesied that passage rate, rather than fermentatin rate, limited extent f ruminal NDF digestin fr bth treatments in this study. Ttal NDF digestin was greater (P.5) fr steers fed DDG vs DCGF, indicating that NDF in DCGF escaping ruminal digestin may be less readily fermented by hindgut bacteria than is escaped DDG fiber. Anther explanatin may be that greater amunts f NANBN (table 4) presented t the dudenum f steers fed DDG diets may stimulate hindgut fermentatin f NDF if a significant fractin f NANBN is nt absrbed in the small intestine. Sants et al. (1984) shwed that much greater amunts f ttal AA disappeared in the large intestine f dairy cws fed DDG diets than fr thse fed diets cntaining sybean meal (SBM), crn gluten meal r wet brewers grains. Plegge et al. (1985) nted that when SBM was replaced with rasted SBM in steers diets, bth ruminal escape f prtein and ttal tract NDF digestin increased. A prcessing intake level interactin (P.2) was nted fr dudenal fluid-phase N

11 PARTICLE SIE, INTAKE AND PROTEIN SOURCE IN STEERS 191 E. > X X X -- ~ ~ ~ r~ 5 B~ X r,. e~ 8 v "O. ~ I e~ X [... P~ [.. r~ I- ce -b t..,, d E._ - -,-.1 e~ -~ -~ r, -~.~. ~ ~. ~ ge'~ 5~

12 .,,~ 192 FIRKINS ET AL. qq q q q ~. q. q e~!-~ I I I I I I m~ m [.., [.., 8 Ou, F. ul,.j ~ r~ ~ ~ ~m ~ g L~ 8 [...,.~.~ ~ 8 2

13 PARTICLE SIE, INTAKE AND PROTEIN SOURCE IN STEERS 19J flw (table 6). The interactin ccurred when chpped hay was fed at high-intake levels, with fluid N flw t the dudenum being lwer (P.5) when DCGF vs DDG was included in the diet. This interactin is prbably due t the trend (P.25) fr lwer fluid flw fr steers fed chpped hay-dcgf vs chpped hay-ddg diets at high intakes (97.2 vs 88. liters/d, respectively). Althugh n differences in ruminal D due t treatment were detected, individual values fr particulate D ranged frm 2.4 t 7. %/h and fluid D ranged frm 5.8 t 15.5 %/h in this study. Apparent OM digestin in the rumen (% OM intake) was negatively crrelated with fluid and particulate D (r = and -.57; P.5 and.1, respectively; table 7). Apparent N digestin in the rumen was negatively crrelated with particulate D (r = --.34). These negative crrelatins indicate that extent f ruminal OM, NDF and N digestin are, in part, cntrlled by ruminal passage rates. A psitive relatinship (r =.75; P.1) was nted between true ruminal OM digestin and ruminal NH3 cncentratin, but a negative relatinship (r = -.44; P.1) was bserved between apparent ruminal N digestin (% intake) and ruminal NH 3. Higher levels f ammniated hay in grund- vs chpped-hay diets, and mre rapid prtelysis f DCGF vs DDG, may explain these relatinships because steers fed grund hay r DCGF treatments had higher apparent ruminal OM digestibilities than did thse fed chpped hay r DDG treatments, respectively. Bergen et al. (1982) nted that increased efficiency f micrbial grwth ften ccurs with increasing ruminal fluid- r particulatephase D due t relatively lwer maintenance energy requirements f bacteria (lsaacsn et al., 1975). Highly significant crrelatins (bth r =.64; P.1) between bth fluid and particulate D and efficiency f MCP synthesis reflect a clse relatinship between these variables in the ruminal envirnment within individual steers, regardless f treatment. Fluid- and particulatephase D were highly crrelated (r =.72; P.O1). A similar relatinship was nted by Mees and Merchen (1984) in sheep. This may be due t enhancement f utflw f sluble r small particulate feed cmpnents by increasing fluid utflw (Teeter and Owens, 1983). Fluid D and ruminal vlume were negatively crrelated. This relatinship, has ften been bserved (F. N. Owens and A. L. Getsch, persnal cmmunicatin), and may be due t an inter- actin in cntrl f ruminal vlume and dilutin rate, maintaining a cnstant fluid flw t the dudenum in individual steers. This study did cnfirm that the lwer tract is an imprtant site f fiber digestin in the ruminant. In every treatment cmbinatin, incrprating DDG vs DCGF in the diet increased NANBN and ttal N flws t the dudenum. Feeding DDG in a high-frage diet may increase quantity f fiber digested in the hindgut, but it is nt knwn whether this effect is due t the escape f DDG fiber r prtein. Significant interactins indicate that levels f feed intake may affect results btained in experiments where frage particle sies and prtein surces are evaluated. Effects f frage prcessing n nutrient digestin shuld nt be generalied since very fine grinding and(r) levels f intake near ad libitum may be necessary t elicit these respnses. L iterature Cited Alwash, A. H. and P. C. Thmas Effect f the sie f hay particles n digestin in the sheep. J. Sci. Fd Agr. 25:139. Annymus Crn Wet-milled Feed Prducts. Crn Refiners Assciatin, Inc., Washingtn, DC. Annymus Feeding Value f Ethanl Prductin By-prducts. Natinal Academy Press, Washingtn, DC. AOAC Official Methds f Analysis. (12th Ed.) Assciatin f Official Analytical Chemists. Washingtn, DC. Beever, D. E., J. F. Celh da Silva, J.H.D. Presctt and D. G. Armstrng The effect in sheep f physical frm and stage f grwth n the sites f digestin f a dried grass. 1. Sites f digestin f rganic matter, energy and carbhydrate. Brit. J. Nutr. 28: 347. Beever, D. E., D. F. Osburn, S. B. Cammell and R. A. Terry The effect f grinding and pelleting n the digestin f Italian ryegrass and timthy by sheep. Brit. J. Nutr. 46:357. Bergen, W. G., D. B. Bates, D. E. Jhnsn, J. C. Waller and J. R. Black Ruminal micrbial prtein synthesis and efficiency. In: F. N. Owens (Ed.) Prtein Requirements fr Cattle: Sympsium. pp Oklahma State Univ. Press, Stillwater. Bergen, W. G., D. B. Purser and J. H. Cline Effect f ratin n the nutritive quality f rumen micrbial prtein. J. Anita. Sci. 27:1497. Blaxter, K. L., N. M. Graham and F. W. Wainman Sme bservatins n the digestibility f fd by sheep, and n related prblems. Brit. J. Nutr. 1:69. Carmer, S. G. and M. R. Swansn An evaluatin f ten pair-wise multiple cmparisn prcedures using Mnte Carl methds. J. Amer. Statist. Assc. 18:66. Chancy, A. L. and E. P. Marbach Mdified reagents fr determinatin f urea and ammnia. Clin. Chem. 8:13. Ellis, W. C., C. Lascan, R. Teeter and F. N. Owens.

14 194 FIRKINS ET AL Slute and particulate flw markers. In: F. N. Owens (Ed.) Prtein Requirements fr Cattle: Sympsium. pp Oklahma State Univ. Press, Stillwater. Erwin, E. S., G. J. Marc and E. M. Emery Vlatile fatty acid analysis f bld and tureen fluid by gas chrmatgraphy. J. Dairy Sci. 44:1768. Faichney, G. J The use f markers t partitin digestin within the gastrintestinal tract f ruminants. In: I. W. McDnald and A.C.I. Warner (Ed.) Digestin and Metablism in the Ruminant. pp Univ. f New England Pub. Unit, Armidale, Australia. Firkins, J. L., L. L. Berger and G. C. Fahey, Jr Evaluatin f wet and dry distillers grains and wet and dry crn gluten feeds fr ruminants. J. Anita. Sci. 6:847. Firkins, J. L., L. L. Berger, G. C. Fahey, Jr. and N. R. Merchen Ruminal nitrgen degradability and escape f wet and dry distillers grains and wet and dry crn gluten feeds. J. Dairy Sci. 67:1936. Gering, H. K. and P. J. Van Sest Frage fiber analyses (Apparatus, reagents, prcedures and sme applicatins). ARS, USDA Handbk N USDA, Washingtn, DC. Getsch, A. L. and M. L. Galyean Influence f feeding frequency n passage f fluid and particulate markers in steers fed a cncentrate diet. Can. J. Anim. Sci. 63:727. Grvum, W. L. and V. J. Williams Rate f passage f digesta in sheep. 6. The effect f the level f fd intake n mathematical predictins f the kinetics f digesta in the reticulrumen and intestines. Brit. J. Nutr. 38:425. Hgan, J. P. and R. H. Westn The digestin f chpped and grund rughages by sheep. 2. The digestin f nitrgen and sme carbhydrate fractins in the stmach and intestines. Australian J. Agr. Res. 18:83. lsaacsn, H. R., F. C. Hinds, M. P. Bryant and F. N. Owens Efficiency f energy utiliatin by mixed rumen bacteria in cntinuus culture. J. Dairy Sci. 58:1645. Jaster, E. H. and M. R. Murphy Effects f varying particle sie f frage n digestin and chewing behavir f dairy heifers. J. Dairy Sci. 66:82. Kaufmann, W., H. Hagemeister and G. Dirksen Adaptatin t changes in dietary cmpsitin, level and frequency f feeding. In: Y. Ruckebush and P. Thivend (Ed.) Digestive Physilgy and Metablism in Ruminants. pp AVI Publishing C., Westprt, CT. Lared, M. A. and D. J. Minsn The effect f pelleting n the vluntary intake and digestibility f leaf and stem fractins f three grasses. Brit. J. Nutr. 33:159. MacRae, J. C. and D. G. Armstrng Studies n intestinal digestin in the sheep. I. The use f chrmic xide as an indigestible marker. Brit. J. Nutr. 23:15. Mees, D. C. and N. R. Merchen Effects f sdium bicarbnate additins t wheat straw (WS)-based diets n rumen turnver rates and nutrient digestibility by sheep. J. Anim. Sci. 59(Suppl. 1): 127. Miller, E. L Evaluatin f fds as surces f nitrgen and amin acids. Prc. Nutr. Sc. 32:79. Mudgal, V. D., R. M. Dixn, P. M. Kennedy and L. P. Milligan Effect f tw intake levels n retentin times f liquid, particle and micrbial markers in the rumen f sheep. J. Dairy Sci. 54:151. Osburn, D. F., D. E. Beever and D. J. Thmsn The influence f physical prcessing n the intake, digestin and utiliatin f dried herbage. Prc. Nutr. Sc. 35:191. Plegge, S. D., L. L. Berger and G. C. Fahey, Jr Effect f rasting temperature n the prprtin f sybean meal nitrgen escaping degradatin in the rumen. J. Anita. Sci. 61:1211. Sants, K. A., M. D. Stern and L. D. Satter Prtein degradatin in the tureen and amin acid absrptin in the small intestine f lactating dairy cattle fed varius prtein surces. J. Anim. Sci. 58: 244. SAS SAS User's Guide: Statistics. Statistical Analysis System Institute, Cary, NC. Staples, C. R., R. L. Fernand, G. C. Fahey, Jr., L. L. Berger and E. H. Jaster Effects f intake f a mixed diet by dairy steers n digestin events. J. Dairy Sci. 67:995. Stkes, M. R., W. D. Steinhur, H. B. Puckett and J. H. Clark Cmpact machine fr feeding at hurly intervals. J. Dairy Sci. 62:17. Tamminga, S Prtein degradatin in the frestmachs f ruminants. J. Anita. Sci. 49:1615. Teeter, R. G. and F. N. Owens Characteristics f water sluble markers fr measuring rumen liquid vlume and dilutin rate. J. Anita. Sci. 56:717. Thmsn, D. J., D. E. Beever, J. F. Celh da Silva and D. G. Armstrng The effect in sheep f physical frm n the sites f digestin f a dried lucerne diet. 1. Sites f rganic matter, energy and carbhydrate digestin. Brit. J. Nutr. 28: 31. Uden, P., P. E. Clucci and P. J. Van Sest Investigatin f chrmium, cerium and cbalt as markers in digesta rate f passage studies. J. Sci. Fd Agr. 31:625. Wald, D. R., L. W. Smith, E. L. Cx, B. T. Weinland and W. L. Lucas, Jr Lgarithmic nrmal distributin fr descriptin f sieved frage materials. J. Dairy Sci. 54:1465. Westn, R. H. and J. P. Hgan The digestin f chpped and grund rughages by sheep. 1. The mvement f digesta thrugh the stmach. Australian J. Agr. Res. 18: 789. Williams, C. H., D. J. David and O. lismaa The determinatin f chrmic xide in faeces samples by atmic absrptin spectrphtmetry. J. Agr. Sci. (Camb.) 59: 381. inn, R. A. and F. N. Owens Rapid prcedure fr quantifying nucleic acid cntent f digesta. In: F. N. Owens (Ed.) Prtein Requirements fr Cattle: Sympsium. pp Oklahma State Univ. Press, Stillwater.