TheAssociation ofTiters toBovineCoronavirus withTreatment forBovine Respiratory Disease andWeight GaininFeedlot Calves

Theassociation betweenbovine respiratory disease (BRD)andantibodytiters tobovine coronavirus (BCV)wasstudied in604calves (19different groupsin4different feedlots from2provinces). Almost allcalves hadantibody titers on arrival intheAlberta feedlot and 82%ofthecalves hadanantibody titer onarrival attheOntario feedlots; titers incalves inAlberta were almosttwiceashighasthosein calves inOntario. Theincidence of infection, inthefirst mo after arrival asjudgedbyseroconversion, rangedfrom61% to100%; titer increases weremuchgreater in calves inOntario feedlots. Titer variables werenotsignificantly related toBRD,except onawithingroupbasis (group wasaconfoundingvariable forBCV-BRDassociations). Given control ofgroupeffects, calves withanantibody titer on arrival appeared tobeprotected against BRD forthefirst 28dinthe feedlot, andtheassociation wasreasonably linear overtherangeof titers. Eachtiter unitonarrival decreased theriskofBRD byabout 0.8x(odds ratio). Titer change was notstrongly related totheriskof BRD andtherelationship wasnot linearovertherangeoftiter changes. Titer change wasstrongly andnegatively correlated withtiter onarrival, andtiter change wasnot significantly related toBRD inthe presence ofarrival titers. Arrival titer retained itsrelationship with BRD inthepresence oftiter data forotherputative pathogens. Each higherunitoftitertoBCV on arrival increased the28-day weight gain(controlling forgroup,initial weight andtheoccurrence ofBRD) byslightly morethan1kg.Titer change wasassociated withdecreased weight gain, wheninitial titer was notinthemodel. Thelackofalinearormultivariable association betweenBCV titerchangeand BRD,andweight gain, mayindicate thatBCV isnotamajorpathogen; or,itslackofsignificance may merely beduetoitsstrong correlationwitharrival titer. Giventhe associations foundinthisstudy, particularly theinterprovincial differences inarrival titers, moreand different approaches tostudying thepossible effects ofBCVonBRD areinorder.