Chemical composition, energy content, intake and in situ crude protein degradability of the forage consumed by goats in a thorn scrubland in the semiarid region of North Mexico

摘要

Currentproteinsystemsforruminantsdescribetheavailabilityoftheproteinconsumedbyruminantsasmetabolizableprotein.Thosesystemsconsiderthattheproteinconsumedbythoseanimalsisincorporatedintotherumenmicroorganismsasmicrobialproteinorthatitflowstothesmallintestinewithoutbeingattackedbytherumenmicroflora.Someofthosesystemsalsoconsidertheprecisedeterminationofthefermentativecharacteristicsoftheprotein,asanimportantpartofthesystemstructure,inordertopredictanimalperformanceortoappropriatelyimplementsupplementationpractices.TheobjectiveofthisstudywastodeterminethenutritivevalueandtoestimatetheproteinruminaldegradationparametersofthedietconsumedbygoatsinathornscrublandinthesemiaridregionofNorthMexico.Threegoatsfittedwithruminalandesophagealcannulae(38#177;1.7kgBW)belongingtoaflockof250animalswereusedtoobtaindietsamplesduringthe1999dryseason(FebruarytoJune)andtoincubatesamplesoftheforageconsumedbytheanimals.Meanwhile,threeintactbucks(38.7#177;7.6)wereusedtodeterminefecalproductionandfromittoestimateOMintake(OMI=OMfecalproduction/undigestiblefractionofthediet).ExtrusasampleswereanalyzedforCP,OM,invitroorganicmatterdigestibility(IVOMD)usingpepsin-cellulase,digestibleorganicmatter(DOM)andmetabolizableenergy(ME).Theextrusasamplescollectedthepreviousmonthwereplacedinnylonbags(5gDM)andincubatedintherumenoftwoofthesamegoatsfor0,3,7,24,48,72and96h.TheproteindegradationcharacteristicsoftheforageconsumedweredescribedusingtheequationP=a+b(1-e-ct).TheCPcontent(%DM),OM(g/kgDM),IVOMD(%),ME(Mcal/kgDM),OMI(g/d)andOMI(g/kgBW0.75/d)were12,822,55,1.7,927and61.3,respectively.Themeanvaluesfortheproteindegradationparameterswere:29.6%forthesolublefraction(a),35.5%fortheinsolublebutfermentablefraction(b),4.0%/hfortheconstantrateofdegradation(c),64.9%forthepotentialdegradation(PD)and48.8%fortheeffectivedegradation(ED).Thesolublefractionrepresentedmorethan60%oftheproteineffectivelydegradedintherumen,whichmayindicatethattherumenmicrobialcapacitytouptakeandutilizethechemicalcompoundscouldhavebeenoverwhelmedintheinitialphaseoftheproteindegradation.Theconstantrateofdegradationandtheeffectivedegradabilityoftheproteinintheforageconsumedbygoatswouldindicateafairlysmallamountofdegradableproteintosustaintheactivityoftherumenmicrobialpopulationduringthedryseason.Resultsfromthisstudysuggestthattherangegoatsmeettheirenergyrequirementsformaintenanceandmediumactivity,althoughinsitudataindicatetheneedforsupplementingasourceofslowlydegradableproteinduringtheharshseason.