Pregnancy rates in heifers and suckled beef cows after synchronized ovulation using PGF2', GnRH, and norgestomet

摘要

Suckled cows and virgin heifers received anovel treatment that included PGF 2", GnRH,and norgestomet, with the objective of inducingestrus in prepubertal heifers and anestroussuckled cows, as well as synchronizing ovulationin estrus-cycling females. The treatmentconsisted of two injections of PGF 2" (day 14and 0) plus 100 Fg of GnRH and a 6-mgnorgestomet ear implant on day 7. The implantwas removed 24 h after the second injectionof PGF2" (day 0), and a second injection ofGnRH was given 30 hours after implant removal.The treated females were inseminated18 hours after the second injection of GnRH orat estrus, if it was detected before the secondGnRH injection. Pregnancy rate in the treatedfemales was greater than in control females thathad received two injections of PGF 2" 14 daysapart and were inseminated at estrus or at onefixed time (60.2 vs. 48%). The treatmentsuccessfully induced a fertile ovulation in previouslyprepubertal heifers and anestrous cows,resulting in 63.5% pregnancies vs. 26.5% forcontrols. In addition, in females not showingestrus, the treatment increased pregnancy ratefollowing a fixed-time insemination (treatmentvs. control; 60.0 vs. 3.8%). We concluded thattreatment with PGF2", GnRH, and norgestometinduced estrus and increased pregnancy rates inprepubertal heifers, anestrous cows, and cyclingfemales.