The effect of wattle tannin on intake, digestibility, nitrogen retention and growth performance of goats in South Africa

摘要

Thisstudywasconductedtodeterminetheeffectofwattletanninextract(WTE)onproteinutilisationbygoatsinametabolismandagrowthtrial.Iso-nitrogenousdiets(18%CP)withthefollowingingredients:filler,sunflowercake,molasses,hominychop,vitamin-mineralmixandlucernehaywereformulatedandmixedwith0,7.5,15,22.5and30gWTE/kgdrymatter(DM).Thedietswerefedtogoatssupplementedwith20%(w/w)nativepasturehay.Inthemetabolismtrialeighteenmale(5Nguniand13Boer)goats,withinaliveweightrangeof21.5to37.5kg(withameanof28.6,S.D.=4.88),wereblockedbyweightandrandomlyassignedtothefivetreatmentrations.IncrementallevelsofWTEinthedietresultedtosmallandnon-significantincreases(P0.05)oftotalintake(g/day)ofdrymatter(DM)(mean1089#177;58.6),organicmatter(OM)(mean902#177;48.3),andnitrogen(N)(mean32#177;1.8)buttheintakeofneutraldetergentfibre(NDF)(mean351#177;17.6)significantlyincreasedlinearly(P0.05)withincreasingWTEdosage.Theapparentdigestibility(g/kg)ofDM(mean(661#177;17.9)didnotchange(P0.05)acrosstreatments.MicrobialNsupply(g/day)anditsefficiencyofsynthesisweresimilaracrossdietarytreatments.Ndigestibilitywasadversely(P0.05)affectedbythelevelsofWTE.InresponsetosupplementationwithWTE,faecalN(mean8#177;0.4g/day)rosewhileurinaryNexcretion(mean13#177;1.0g/day)wasnotaffected,andneitherwasNretention(mean10#177;0.7g/day).Inthegrowthtrial,SouthAfricanindigenousNguniandBoergoats(n=26)wereused.Goatswereaboutat8-24monthsofagewithliveweightsrangingfrom11to28kg(mean17.8,S.D.=3.80kg).BoergoatsconvertedfeedsignificantlymoreefficientlythanNgunigoats(0.21vs.0.17ggain/gfeed,P0.001).TheseresultsindicatethatWTEgivenasdietarysupplementisunlikelytoimprovetheproteinstatusandthereforegrowthperformanceofgoatstoaconsiderabledegree.