A studywasconductedtoevaluatetheeffectofhumanchorionicgonadotropin(hCG)
administration 4or6daysaftertimedAI(TAI)onP4 concentration andpregnancyout-
comes inrepeatbreedingdairycows.AllcowsweretreatedbyCosynchprotocolbefore
being assignedinto3groups:CON(n = 139):didnotreceivehormonaltreatments;D4
(n = 136):received1500IUhCG4dayspostTAI;andD6(n = 131):received1500IUhCG
6 dayspostTAI.PlasmaP4 concentration wasevaluatedonDayofhCGand12days
post TAI.PregnanciesperAI(P/AI)onDay45weregreaterforD6(38.9%)thanCON
(30.9%) groups.Pregnancylosses(PL)werelowerforD6(15.0%)andD4(26.7%)than
CON (37.7%)groups.TreatmentbyseasonrevealedagreaterP/AIandlowerPLforD6
(30.3% and18.2%)andD4(33.3%and31.0%)thanCON(19.2%and58.3%)groupsdur-
ing summer,whileP/AIwasgreaterforD6(57.1%)thanD4(30.6%)andCON(37.9%)
groups duringwinter.TreatmentbyparityindicatedagreaterP/AIforD4(46.4%)andD6
(31.6%) thanCON(15.8%)groupswithinprimiparouscows.Pregnancylosseswerelower
for D6(15.1%)thanCON(36.5%)groupswithinmultiparouscowswhileD4tendedtobe
lower (13.3%)thanCON(50.0%)groups.PlasmaP4 concentration onDay12postTAIwas
higher fortreatedthanforCONgroups.ApplyinghCG6daysafterTAIwasbeneficialin
improving P/AIeitherinsummerorwinterasaresultofreducingPLandincreasingP4
concentration.