Estrus and pregnancy after synchrony with lutalyse in conjunction with Syncro-Mate-B

Estrous response and pregnancy rates are decreased for cows given Syncro-Ma te-B (SMB) during metestrus (Day 1 to 5 of an estrous cycle). Data indicate these decreases are due, in part, to retention of a functional corpus lute um(CL). Our objective was to determine whether PGF2 alpha administered in c onjunction with SMB would improve estrous response and pregnancy rates in m etestrous cows with no detrimental effects to cows in other stages of the e strous cycle. Three hundred seventy-three suckled beef cows were observed f or estrus for 21 d before SMB administration to determine stage of an estro us cycle. Blood samples were collected 14 and 7 d before treatment and at S MB administration. Serum was assayed for concentration of progesterone to v erify stage of estrous cycle or noncyclicity. All cows received the standar d SMB regime and were allotted by age and stage of cycle to one of two grou ps. Cows denoted SMB + L received 25 mg of PGF2 alpha 8 d after implantatio n, whereas cows denoted SMB served as controls. On Day 10, SMB implants wer e removed and females were observed for subsequent estrus. At this time, ca lves were removed from their dams for 48 h. Artificial insemination was per formed 12 hr after observation of a standing estrus. Timed insemination was performed at 48 hr after implant removal for cows not inseminated at 24 or 36 hr after implant removal. Interval to synchronized estrus (within 5 d o f implant removal) was lengthened for metestrous cows compared to cows in o ther stages of the cycle irrespective of treatment (P < 0.001). Cows receiv ing PGF2a had a greater pregnancy rate at 5 d compared to controls (P = .06 72). Interval to estrus, estrous response, and pregnancy rate to AI at d 28 or end of breeding season were not affected by administration of PGF2a in conjunction with SMB when compared to the standard SMB protocol. (C) 2001 b y Elsevier Science Inc.