Protein-energy supplementation for cattle raised on tropical pastures: Theoretical aspects and main results published in Brazil

摘要

Since1940,thepaperspublishedinscientificjournalsreportedthatgrazingisthemosteconomicwaytofeedcattleinBrazil.Duringthewetseasoncontinuousgrowthofanimalsisobserved,butinthedryseasonthereisalmostnoweightgainortheweightgainobtainedinthewetseasonislost.Duringthedryseasonthehighindigestiblefibrecontentoftropicalpasturesandtheverylowcrudeproteinintakearethemainfactorsfortheweightloss.Whenforageavailabilityistoolow,anenergeticsupplementmustbegiven,becauseproteinsupplementsalonedonotovercometheenergeticdemands.UreaisanitrogenfeedstuffofthelowestcostavailableinBrazilandissourceofN-NH3forrumenfibrolyticmicroorganismswhichuseammoniaforgrowth.TheeconomicaspectsofsupplementationduringthewetseasonhavesofarnotbeeninvestigatedinBrazil.WhencattlereceivesupplementscontaininglargeamountsofNaCl(150-300gkg-1),theanimalsexhibitaconstantpatternofnutrientintakefromthesupplement,gofrequentlytothetroughandconsumemorewaterthannon-supplementedanimals.Althoughmuchresearchhasbeendone,andpositiveeffectsforanimalgrowthandimprovementofherdreproductiveparameterswereconfirmed,therehasbeennoinvestigationonthereductionofphosphorussupplementationwhencattlearefedwithprotein-energeticsupplements.Finally,farmersandextensionworkersshouldknowthattheresponseofanimalstoprotein-energeticsupplementationisestablishedbyMitscherlich'slaw;e.g.non-lineargrowthanddecreasingperformanceassupplementintakeincreases.