Mineral supplementation and reproductive rate of beef cows grazing tropical natural pastures in Malawi (part I)

[摘要] AnexperimentthatstartedinJune1984wasconductedatKutiRanchnearSalimainthecentralregionofMalawi,involving161Brahmancrossbredcowsdividedintofourgroupsofabout40cows.Theobjectivewastodetermineresponseofcowstomineralsupplementationidentifiedasdeficientinapreviousstudy.Theanimalsgrazedtropicalnaturalpasturesandweregivenmineralsupplementsthroughouttheyear.Thetreatmentswereasfollows:Group1--salt+phosphorus,Group2--salt+phosphorus+copper+cobalt+selenium,Group3--saltonly,Group4--salt+copper+cobalt+selenium.Phosphoruswasgivenasamixtureofmonocalciumanddicalciumphosphate,copperascopperglassboluses(includingcobaltandselenium)andsaltassodiumchloridecrystals.Cowswerenotsupplementedthefirstbreedingseason.Supplementationofsaltandphosphorusstartedthethirdbreedingseasonin1986.Thus,theexperimenthadcompletetreatmentsin1986-87breedingseason.Sampleswerecollectedofboneandliverbiopsy,blood,andforagesaccordingtospeciesgrazedbythecattleandthesoiluponwhichtheforagegrewandanalyzedforanumberofminerals.Therewasnoeffectofphosphorusorcopperonpregnancydiagnosisrate.Also,therewasnoeffectofphosphorusoncalvingrateofthecowsbasedonresultsfortwoyearsofmineralsupplementation.Mineralsupplementationdidnotincreasethecalvingratesignificantlyfromtheaverageof48%fortheanimalssupplementedwithonlysaltduringthedryseason.Mineralanalysisindicatedthatphosphorus,copperandzincintheanimaltissues,forageandinsoilweredeficient.However,phosphorussupplementationdidnotraisethephosphorusconcentrationsintheboneabovecriticallevel,whereascoppersupplementationraisedcoppertwofold.

[学科分类] 农业科学（综合）