Kinetics of macro-mineral release in the rumen from Kikuyu grass (Pennisetum clandestinum) harvested at two cutting intervals

摘要

Toestimatetheparametersofruminalcalcium(Ca),phosphorus(P),magnesium(Mg)andpotassium(K)kineticsreleasefromkikuyugrass(Pennisetumclandestinum)harvestattwocuttingages,aninsitutestwasdevelopednbsp;utilizingfourHolsteinrumencannulatedfemales.Threesamplesofthisgrasswereharvestedat32and58ofregrowthdaysfromthesamepaddockandwereanalyzedfordrymatter(DM),Ca,P,MgandK.28sub-samplesof3.0gapproximatelyweretakenfromeachsample.Theywerepackedinnylonbagsof5x10cmandtheywereincubatedduringseventimes(0,2,6,12,24,48,y72h)intherumenofthefourcannulatedHolsteinfemales(onebagbyeachtimeandbyeachsample).Atendofincubationperiods,thebagswerewashedwithtapwateranddriedat60oCduring48h.TheresiduesfromthefourbagsofeachincubationtimeandofeachsampleweremixedandwereevaluatedforDM,Ca,P,MgandK.Thepercentageofrumenmineralreleasewasestimatedbydifferencebetweentheinitialandfinalmineralquantityineachnylonbag.Thecuttingagedidnotaffectthemineralcontentnortheruminalmineralreleasekineticparameters.Kwasthemineralwithhighestconcentration(4.0%),followedbyP(0.47%,Ca(0.28%)andMg(0.26%).DuringthetwofirstincubationtimestherumenCawasretainedbygrasssamplesand,inconsequence,thesolublefraction(a)ofthismineralwasnegative.Fortheothermineralsahighafractionwasobservedoscillatingbetween70.4%inMgto85.6%inKatharvestsof58daysofregrowth.Thepotentiallyreleasablefraction(b)washighinCa(91.3%)butlowintheotherminerals.Cashowedadelayinthebeginningofthequickphaseofreleaseoscillatingbetween5.02and7.79h.Theeffectiveruminalreleasewasdifferentamongallmineralsbeingamongnbsp;lowestinCa(43.8%)andhighestinK(96.8%),andintermediateinMg(84.6%)andinP(90.4%).TheexcessKcontentandeffectiveruminalreleaseinkikuyugrassmayaffecttheCaandMgutilization.