Oven drying improves the nutritional value ofCalliandra calothyrsus andGliricidia sepium as supplements for sheep given low-quality straw

J Sci Food Agric 1997, 75, 503È510

Oven Drying Improves the Nutritional Value ofcalothyrsus and sepium asCalliandra Gliricidia

Supplements for Sheep Given Low-Quality StrawJong-Ho Ahn,* Robert Elliott” and Barry W Norton°

Department of Agriculture, The University of Queensland, Brisbane, Queensland 4072, Australia

(Received 26 November 1996 ; revised version received 8 April 1997 ; accepted 2 May 1997)

Abstract : Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Cal-liandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) tosheep (n \ 3) given a basal diet of barley straw ad libitum. Tree leaves were fedeither freshly harvested (F\ fresh) or after drying at 60¡C in a forced draughtoven (D\ dried). Voluntary intakes, digestibility and aspects of nitrogen (N) andphenolic compound metabolism were measured in all sheep. Drying decreasedthe condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg~1 DM).Total phenolics (TP) were signiÐcantly decreased when Gliricidia was dried (F 39,D 21 g TP kg~1 DM), and CT content was reduced from 20 g CT kg~1 DM tozero. Sheep given Gliricidia had higher rumen ammonia concentrations (73È85 mg N litre~1) than did sheep given Calliandra (37È40 mg N litre~1). For bothspecies, drying signiÐcantly increased the voluntary consumption of straw,increased DM digestibility, decreased faecal N excretion and increased Nbalance. For calliandra, drying decreased the apparent degradability of N in therumen (DNR) from 0É40 to 0É28 g N g~1 N ingested, and increased the apparentdigestibility of N (ADN) in the post-ruminal tract from 0É20 to 0É52 g Nabsorbed g~1 N Ñowing into the small intestines. For Gliricidia, DNR decreasedfrom 0É64 to 0É51 and ADN increased from 0É41 to 0É56. There were no signiÐ-cant e†ects of drying on rates of microbial N synthesis. The above changes werediscussed in relation to changes in tannin content and it was concluded thatdrying facilitates the formation of proteinÈtannin complexes which protect pro-teins from degradation in the rumen. These proteins are subsequently released inthe small intestines, thereby promoting an increased efficiency of dietary N uti-lisation.

J Sci Food Agric 75, 503È510 (1997)No. of Figures : 0. No. of Tables : 5. No. of References : 34

Key words : condensed tannin, Gliricidia, Calliandra, nitrogen metabolism, sheep,drying e†ects

INTRODUCTION

Tree leaves are used as sources of feed for ruminants inmany di†erent areas of the world and there is an

* Present address : Department of Dairy Science, Faculty ofAgriculture, 67 Seockjeong-ri, Anseung-up, Kyunggi-do,Republic of Korea 465-749.” Present address : Colbourn-Dawes Australia (Pty) Ltd, 46Industrial Avenue, Wacol, Queensland 4076, Australia.° To whom correspondence should be addressed.

increasing interest in trees as a fodder source for rumi-nants. L eucaena leucocephala (Lam) de Wit (L eucaena),Gliricidia sepium (Jacq) Steud (Gliricidia) and Calliandracalothyrsus Meissn (Calliandra) are tree species whichhave their origin in central America, and have been dis-tributed widely throughout the tropics as useful foddertree species. However, all species have anti-nutritivefactors which may limit use. For example, L eucaenacontains mimosine and its goitrogenic metabolite dihy-droxypyridone (DHP) (Hegarty et al 1979), Gliricidia is

5031997 SCI. J Sci Food Agric 0022-5142/97/$17.50. Printed in Great Britain(

504 J-H Ahn, R Elliott, B W Norton

of low and variable palatability to animals (Lowry1990 ; Simons and Stewart 1994) and Calliandra con-tains high levels of condensed tannins which mayrestrict intake (Palmer et al 1994). New technologiesand management techniques are being developed toovercome these limitations, eg the introduction of DHPdegrading organisms into the rumen of animals fed L eu-caena (Jones 1994).

Wilting has been reported as a means of increasingthe acceptance of Gliricidia in Indonesia (Nitis 1986),and mixing fresh leaves with other forages alsoimproves palatability (Lowry 1990). High coumarinlevels in leaves have been implicated in the variableacceptability of Gliricidia (Stewart 1996). Despite highconcentrations of condensed tannins, fresh Calliandraappears to be well accepted by sheep and goats(Kochapakdee 1991), but wilting depresses digestibilityand voluntary intake by sheep (Palmer and Schlink1992). However when Calliandra was provided as a sup-plement (30% intake) to rice straw, drying improved thenutritive value of the tree leaves (Robertson 1988). Ahnet al (1989) reported that oven drying (60¡C) markedlyreduced the tannin content of Calliandra and eliminatedtannins in Gliricidia. It seems possible that wilting ordrying may improve palatability and/or nutritive valuepartly or fully by its e†ects on tannin content and com-position. The following experiment was designed toinvestigate the e†ects of drying on phenolic and tanninmetabolism, nitrogen and organic matter digestion andutilisation in sheep fed Gliricidia and Calliandra as sup-plements to a low-quality straw diet and to identify amechanism by which drying might improve nutritivevalue.

MATERIALS AND METHODS

Feed preparation and feeding

Leaves and shoots of Gliricidia and Calliandra werehand harvested as a 6 month regrowth from 4-year-oldtrees grown at the University of Queensland ResearchFarm at Mt Cotton in south-eastern Queensland. TheCalliandra germplasm was originally obtained fromnaturalised populations in the Bogor region of Indone-sia. Gliricidia sepium seed from Tobago, Thailand andIndonesia (Bali) was introduced to the farm in 1980,and all provenances were judged the same after studiesof comparative morphology. The forage to be fed driedwas harvested and dried in a forced draught oven for48 h at 60¡C. Fresh forage was harvested from cutbranches of Calliandra and Gliricidia and placed inbuckets of water in a cool room (5¡C). Leaves wereremoved daily from the branches and fed to the sheep.Barley straw was obtained from a commercial supplierand cha†ed prior to feeding.

Experimental design and animal management

Six Merino ] Border Leicester wethers were each Ðttedwith a permanent rumen cannula (110 mm internaldiameter) and T-piece cannula in the abomasum,approximately 8 cm from the pylorus. In the week fol-lowing surgery, the sheep were housed in individualcages and fed barley straw ad libitum (50% more thanprevious dayÏs intake) and 100 g of sunÑower meal perday. After this time, three sheep were each o†ered driedCalliandra (400 g dry matter (DM) day~1) and theremaining three sheep each o†ered dried Gliricidia(400 g DM day~1). These legumes were provided inaddition to the basal diet of barley straw and sunÑowermeal. After 1 month on these diets, sheep were trans-ferred to an air-conditioned animal house at the Uni-versity campus and o†ered a diet of barley straw (adlibitum) plus 200 g of either dried Calliandra or driedGliricidia. The legumes were fed from continuous over-head feeders throughout 24 h. This regime lasted for 28days (period 1), after which time fresh legumes were fedin place of dried legumes being o†ered for 28 days(period 2) with the same measurements. Both frozen anddried supplements of Calliandra were consumed withinminutes of presentation, but Gliricidia supplements,although totally consumed over a day, were eaten lessreadily.

Experimental measurements

Digestibility and nitrogen balance measurementsIn period 1, total urine, and faecal outputs were col-lected daily over a 7-day period following a 21-dayadaptation to these diets and in period 2, a 14-dayadaptation period was used. Daily outputs of faecesfrom each animal were measured and 10% subsampleswere composited for drying at 60¡C in a forced draughtoven. A second subsample was freeze-dried for sub-sequent tannin analysis. Urine was collected daily inbuckets containing 20 ml of glacial acetic acid, and sub-samples (10% volume) removed each day and bulkedfor subsequent analysis.

Digesta Ñow from the stomachLiquid digesta Ñow at the abomasum was estimatedusing 51Cr EDTA (Downes and McDonald 1964 ;Weston and Hogan 1967). Ytterbium quantitativelyrecovered in faeces was used as the solid phase marker(Coleman et al 1984 ; Teeter et al 1984 ; Siddons et al1985). Incorporation of 35S-labelled sodium sulphateinto microbial cystine was used to estimate the propor-tion of microbial protein in abomasal digesta (Elliottand Armstrong 1982). Approximately 2É2 g of ytterbium(as ytterbium acetate) was dissolved in 160 litres ofwater. Cha†ed barley straw (5 kg) was soaked in thissolution for 3 days. After this time the straw was dried

E†ects of drying on nutritive value of fodder trees 505

in a forced draught oven at 60¡C (Teeter et al 1984).During each 8 day sampling period, ytterbium treatedstraw (50 g) mixed with untreated straw was given dailyto each sheep which also received a continuous intraru-minal infusion of a solution (250 ml) containing 51Cr-EDTA (3É8 MBq) and (7É8 MBq). In the last 2Na235SO4days of this period, abomasal samples (8 ] 200 ml) werecollected from each sheep at 09 :00, 13 :00, 18 :00 and23 :00 h. These samples were bulked and mixed well anddivided into three portions. One portion was separatedthrough cheesecloth into Ðltrate and particulate matteras described by Faichney (1980). The concentrations ofnitrogen, 51Cr, Yb and organic matter was determinedin each fraction. A second portion of whole abomasaldigesta was freeze-dried and ground for the determi-nation of the speciÐc activity of cystine 35S. The remain-ing quantity of whole digesta was centrifuged initially at2000 ] g for 10 min to separate feed particles and thesupernatant centrifuged at 20 000] g for 20 min toobtain a microbial fraction which was freeze-dried.

Analytical methods

Frozen (fresh) samples of Calliandra and Gliricidia werefreeze-dried before analysis for the following com-ponents. The dry matter content of barley straw, oven-dried Calliandra and Gliricidia feed, feed refusals andfaeces were determined after drying the samples at 60¡Cfor 48 h in a forced draught oven while organic matterin this fraction was determined by ashing for 3 h at500¡C. Total nitrogen contents of feeds, abomasaldigesta and urine were determined by the Kjeldahlmethod (AOAC 1980).

Rumen ammonia concentrations were determined bysteam distillation and titration, while concentration andmolar proportion of the volatile fatty acids were deter-mined in the rumen liquor samples by gas chromatog-raphy following deproteinisation with phosphoric acid.

The condensed tannin contents of feed, faeces andabomasal digesta were measured by the vanillinÈHCl

method (Broadhurst and Jones 1978). The total phenol-ic contents of feed digesta and urine were measured bythe Folin Denis reagent (Burns 1963).

Measurement of the ytterbium content of feed, faecesand digesta was conducted by atomic absorption spec-trophotometry (AA-875, Varian). Samples (0É5 g) weredigested in perchloric/nitric acid and diluted with tripledeionised water before measurement.

Statistical analysis

The experiment was statistically analysed as 2 (treespecies)] 2 (dried or fresh) factorial with three sheepper treatment cell. Di†erences between treatments weretested by least signiÐcant di†erence (LSD) following theanalysis of variance (Steel and Torrie (1980).

RESULTS

Chemical composition of feeds

Table 1 shows the mean values for the nitrogen, organicmatter, total phenolics and condensed tannins of a basaldiet, barley straw. Values for Calliandra and Gliricidiawere determined for both freeze- and oven-dried leaves,respectively, and are also presented.

Concentrations of ammonia and volatile fatty acids inrumen liquor

Oven drying of dietary legumes had no e†ect (P\ 0É05)on rumen ammonia or total volatile fatty acid concen-trations (Table 2). The fermentation pattern in therumen was not changed by either oven drying or by thespecies of browse used. However, ammonia concentra-tions were lower (P\ 0É05). in the rumen Ñuid of sheep

TABLE 1Chemical composition (g kg~1 DM) of barley straw and freeze- or oven-dried Calliandra

calothyrsus and Gliricidia sepium

Feed Nitrogen Organic T otal Condensedmatter phenolics tannins

Barley straw 3É0 922 6É2 NDCalliandra

Freeze-dried 37É8 956 188É2 117É1Oven-dried 38É2 955 176É5 82É2

GliricidiaFreeze-dried 34É6 944 38É8 19É9Oven-dried 31É8 946 21É2 NDa

a ND, not detected by vanillin-HCl.


TABLE 2InÑuence of oven-drying browse legumes on ammonia and volatile fatty acid concentration in the rumen Ñuid

of sheep fed fresh and dried Calliandra and Gliricidia

Measurement Calliandra Gliricidia SEM SigniÐcance ofdi†erence betweena

Fresh Dried Fresh DriedT ree Form of

species feed

Ammonia N (mg litre~1) 37 40 85 73 7É7 * NSVolatile fatty acids (mmol litre~1) 91 101 131 107 12É6 NS NSProportions (mmol mol~1)

Acetic 767 752 740 756 12É5 NS NSPropionic 144 168 203 163 9É1 * NSn-Butyric 74 76 54 58 6É8 * NSiso-Butyric 14 0 1 2 7É3 NS NSn-Valeric 19 4 0 1 0É9 NS *iso-Valeric 6 0 0 0 3É3 NS NSTotal other 39 4 1 3 2É5 * *

a SigniÐcance of di†erence between means : * P\ 0É05, ** P\ 0É01, NS not signiÐcant.

fed Calliandra than in the rumen Ñuid of sheep givenGliricidia.

Intake, digestibility of dry matter and nitrogen utilisation

Sheep readily accepted Calliandra, but Gliricidia leafwas eaten reluctantly even after drying. Dryingincreased (P\ 0É01) the straw intake of sheep o†eredboth Calliandra and Gliricidia and there was no signiÐ-cant (P[ 0É05) e†ect of legume type on straw intake(Table 3). The apparent digestibilities of dry matter and

nitrogen retention were all higher (P\ 0É01) when thebrowse supplements were fed dried rather than fresh.The change from dried to fresh supplements resulted inan immediate decrease in straw intake although thesupplements themselves were rapidly consumed.

The decrease in intake was also associated withdecreased (P\ 0É01) DM digestibilities in sheep fedfresh Calliandra and Gliricidia. The change from driedto fresh legumes also resulted in a reduction in theapparent digestibility of nitrogen (P\ 0É01), and nitro-gen retention in sheep fed fresh Calliandra (P\ 0É01)was particularly low.

TABLE 3InÑuence of drying browse legumes on intake of barley straw, digestibility of DM, N digestibility and N Ñow

along the digestive tract of sheep.


Fresh Dried Fresh DriedT ree Form

species of feed

Dry matter (g day~1)Straw intake 436 691 392 679 64É5 NS **Total intake 640 891 593 880 64É6 NS **Leaving stomach 344 559 323 477 41É8 NS **In faeces 405 365 362 352 37É4 NS NS

NSDry matter digestibility (g g~1) 0É363 0É590 0É423 0É605 0É026 NS **Nitrogen (g day~1)

Total intake 9É2 9É7 8É3 8É5 0É21 ** NSIn faeces 8É6 5É8 6É3 4É5 0É31 ** **In urine 2É4 1É4 2É9 2É6 0É56 NS NSN balance [1É7 2É5 [0É9 1É4 0É48 NS **

Apparent N digestibility (g g~1) 0É073 0É399 0É246 0É474 2É69 ** **

a SigniÐcance of di†erence between means : ** P\ 0É01, NS not signiÐcant.


TABLE 4InÑuence of drying Calliandra and Gliricidia on rumen microbial protein synthesis and digestibility of N in the

post-ruminal tract of sheep



species of feed(S) (F)

N leaving the stomach (g day~1)Total non-ammonia N 10É8 12É1 10É7 10É3 0É92 NS NSMicrobial N 5É3 5É1 7É7 6É1 0É64 * NS

Microbial N synthesised per kg 14 15 27 14 2É7 NS *organic matter apparentlydigested in the rumen

Apparent degradability of 0É402 0É278 0É639 0É506 0É0733 ** NSfeed N in rumen (g g~1)

Apparent N digestibility in 0É204 0É521 0É411 0É563 0É0363 ** **post-ruminal tract (g g~1)


There was an apparent gain of nitrogen across therumen of sheep on all dietary treatments. The extent ofmicrobial protein synthesis was lower (P\ 0É05) in therumen of sheep o†ered Calliandra (either fresh or dry)and it was reÑected in a lower efficiency of microbialprotein synthesis (P\ 0É05) than sheep fed fresh Glirici-dia (Table 4). However, oven-dried Gliricidia showedsimilar values to both treatments of Calliandra. Thedigestibility of nitrogen in the post-ruminal tract waslower (P\ 0É01) when fresh browse replaced the oven-dried material.

Disappearance of total phenolics and condensed tanninsin digestive tract

There were substantial losses of both total phenolicsand extractable condensed tannins across the rumen ofsheep fed fresh or dried Calliandra. The digestion ofextractable condensed tannins was complete in the post-ruminal tract of sheep given both browse legume sup-plements. Although the digestibility of total phenolics inthe post-ruminal tract of sheep fed fresh and dried Gliri-cidia was similar (c 0É67), no extractable condensed

TABLE 5InÑuence of over drying Calliandra and Gliricidia on the disappearance of total phenolics and condensed

tannins in the digestive tract of sheep



species of feed(S) (F)

Total phenolics (g day~1)Intake 41É1 39É6 10É2 8É5 0É46 ** **Leaving stomach 18É4 22É7 6É5 7É4 1É01 ** *Faecal excretion 3É2 3É4 2É4 2É6 0É51 NS NSUrinary excretion 18É0 8É9 12É2 9É1 2É61 NS NS% Disappearance

In rumen 55É5 42É7 37É2 13É7 6É33 ** *Post-rumen 37É0 48É7 40É2 56É5 2É54 ** *

Condensed tanninsIntake 23É9 16É4 4É0 NDLeaving stomach 7É8 6É8 ND ND% disappearance in rumen 67É5 60É0 100É0 ND



tannins were recorded in abomasal digesta of sheep fedfresh Gliricidia (Table 5).

DISCUSSION

The e†ects of drying on N digestion and utilisation

The nutritive value of both browse tree species as sup-plements to barley straw was improved by drying. Thegreatest e†ect was an increased voluntary consumptionof barley straw (58È73% increase) and an improveddigestibility of dietary dry matter (from 0É40 to 0É60).Terrill et al (1989a) found that Ðeld drying Sericea lespe-diza (L espedeza cuneata) increased voluntary intake anddigestibility of high tannin varieties but had no e†ect onlow tannin varieties. Drying also decreased faecal Nexcretion and improved N balance in sheep given bothdiets. There were also signiÐcant di†erences between thespecies in nutritive value. It is proposed that drying mayhave its major e†ect through N metabolism. Firstly,drying denatures soluble plant proteins, decreases deg-radation in the rumen and may increase the quantity ofamino acids available for absorption at the intestines(Beever et al 1976). Secondly, drying may also denaturepotentially toxic substances in the diet and/or modifythe biological activity of substances such as condensedtannins. In this case, the e†ect will vary depending onthe nature of the tannins involved. Although tanninsnormally bind to proteins during passage through therumen, and release protein for absorption at the smallintestine, drying may disrupt this process, increasedietary protein degradation in the rumen, and decreaseprotein availability in the small intestine. If binding toplant proteins during mastication is irreversible, boundproteins will not be released thereby limiting N avail-ability in both the rumen and small intestine. Alterna-tively, drying may facilitate tannin binding to bothsoluble cell proteins and the cell wall, in which case,drying would decrease digestion in the rumen, and ifthese proteins are released in the small intestine,increase post-ruminal protein absorption. This hypothe-sis is supported by this study.

The proteins from fresh Calliandra were poorlydigested (40%) in the rumen when compared with theproteins of fresh Gliricidia (64%) and, in both cases,drying decreased degradability of proteins in the rumen,but increased digestibility in the small intestine and Nretention in the tissues. Although the di†erences indegradabilities between plant species was associatedwith corresponding di†erences in ruminal ammoniaconcentrations and rates of microbial N synthesis, therewas no signiÐcant e†ect of drying on these measure-ments. Drying not only decreased the intake of bothtotal phenolics and condensed tannins, but also shiftedthe site of digestion of these compounds. For bothspecies, drying decreased digestion of phenolics in the

rumen and increased the amount digested in the lowerdigestive tract. It seems likely that drying increased phe-nolic (tannin) binding to proteins, which decreased bothprotein and phenolic digestion in the rumen, and thatphenolicÈprotein complexes were fully degraded duringpost-ruminal digestion. The extent to which tannins canbe speciÐcally implicated in these events will be dis-cussed later. Palmer and Schlink (1992) reported thatdrying depressed both voluntary consumption anddigestibility of fresh Calliandra for sheep, and have sug-gested that Calliandra is best used fresh rather thandried when o†ered as the sole feed. In the present study,dried Calliandra proved to be a more e†ective supple-ment (200 g DM/d) than fresh Calliandra, with driedleaf stimulating the intake of low-quality straw andincreasing diet digestibility. These apparently conÑictingobservations may be attributed to small amounts ofdried Calliandra correcting a nutrient imbalance in therumen, thereby stimulating both intake and rates ofdigestion in the rumen.

The drying of tree leaves signiÐcantly increased boththe overall digestibility and post-ruminal digestibility ofN from both Calliandra and Gliricidia. Armstrong et al(1977) found post-ruminal N digestibilities of 0É695 forsheep on urea diets and 0É708 on hay and concentratediets. In the present study, post-ruminal N digestibilitywas much lower for dry (0É52, 0É56) and fresh (0É20,0É41) Calliandra and Gliricidia, respectively. These lowvalues are possibly associated with a high content ofplant protein complexed with phenolics/condensedtannins in post-ruminal digesta. It is also possible thatfree condensed tannins are highly reactive with an pre-cipitate microbial and digestive enzymes (Barry andManley 1986). The destruction of tannins and possiblyother toxic factors by drying Calliandra may explain thesigniÐcant improvement in the post-ruminal digestibilityof digesta protein following drying. This observationsupport the view that excess tannin could limit nitrogenavailability in the post-ruminal tract (Barry 1989).

Drying and the metabolism of phenolics and condensedtannins

The present study supports previous Ðndings whichhave shown that drying decreases the total phenolic andextractable condensed tannin content of both Gliricidiaand Calliandra (Ahn et al 1989). It was also clear thatdrying altered the nature of total phenolics in both Cal-liandra and Gliricidia ; drying reduced the degradationof phenolics in the rumen and increased absorptionfrom the small intestine. The reduction in measurabletannin content by drying may arise in a number ofways. There may be oxidative destruction of the reactivestructure, polymerisation of tannins or the formation oftanninÈprotein or tanninÈÐbre complexes. The methodsused in the present experiment only isolated free tannins


(those extracted in acetone/water), and the e†ects ofdrying on complex formation was not measured.However, in other studies with Calliandra, Norton andAhn (1997) found that drying decreased the condensedtannin (vanillinÈHCl) content from 96 to 69 g kg~1DM, and increased the percentage bound in tannin-protein complexes from 2É5 to 11É8%. Similarly, Perez-Maldonado and Norton (1996) reported that protein-and Ðbre-tannin complexes represented 16É3 and 20É9%,respectively, of the total tannin (butanolÈHCl) content(75 g kg~1 DM) for dried Calliandra. These resultssuggest that the apparent loss of extractable condensedtannins in Calliandra on drying (29É8%) could beaccounted for by the formation of proteinÈtannin andÐbreÈtannin complexes which were not detected by themethods used in this experiment.

Terrill et al (1989a) also reported a signiÐcant loss ofextractable condensed tannins (vanillinÈHCl) whenSericea lespediza (L espedeza cuneata) forage was pre-served in di†erent ways. Both high (106 g kg~1 DM)and low (53 g kg~1 DM) tannin forages showed asimilar reduction (53%) when oven dried. In anotherstudy, these workers found that Ðeld drying decreasedtannin content and increased voluntary intakes, digest-ibility and nitrogen retention by sheep given hightannin (181 g kg~1 DM) varieties of Sericea lespediza.There were no signiÐcant e†ects of drying on low tannin(87 g kg~1 DM) varieties of this forage (Terrill et al1989b).

However, the e†ects of drying on Gliricidia tanninsare less clear. Firstly, the level of tannins in fresh leafwas much lower than that in Calliandra and, secondly,drying removed all extractable tannins. After correctionfor endogenous secretions (2 g N day~1), the truedegradability of proteins in the rumen of sheep givenfresh Gliricidia was high (0É88) and not dissimilar fromthat found for plants which do not contain tannins(Norton and Poppi 1995). Drying reduced true proteindegradability to 0É73, which may be explained bygreater binding of tannins to proteins and/or adecreased solubility of plant proteins arising from heatdenaturation (Beever et al 1976). In contrast to Cal-liandra, the condensed tannins of Gliricidia appear tohave only minor e†ects on nitrogen metabolism in therumen. Condensed tannins in abomasal digesta arethought to be released by low pH (\3É5) from complex-es of protein and Ðbre (Jones and Mangan 1977) andshould be present as free (extractable) tannins inabomasal digesta. No free tannins were released in theabomasum of sheep fed Gliricidia, yet protein (N)digestibility was improved on the lower digestive tractof sheep given dried Gliricidia. It is possible that anti-nutritive compounds other than tannins in Gliricidiacould have been destroyed by drying, and may explainthe observed improvement in post-ruminal nitrogenabsorption. Coumarin and o-coumaric acid have beenisolated from gliricidia by Griffiths (1962) and signiÐ-

cant amounts of hydrocyanic acid and nitrate have alsobeen detected by Manidool (1985). The high coumarincontent of Gliricidia has been related to the low palat-ability of this species.

In conclusion, oven drying resulted in markedchanges in tannin content of both fodder tree leaves,and these changes led to improved nutritive value ofthese leaves in low quality diets for sheep. However, it isnot possible to ascribe speciÐc e†ects to condensedtannins, and further experiments are planned, usingpolyethylene glycol (PEG) as an inhibitor of tanninaction, to determine the nutritional signiÐcance of hightannin concentrations in fodder tree leaves.

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Documents

Oven drying improves the nutritional value ofCalliandra calothyrsus andGliricidia sepium as supplements for sheep given low-quality straw