COMPARAÇÃO DE PROTOCOLOS PARA INSEMINAÇÃO ARTIFICIAL EM TEMPO FIXO COM UMA OU DUAS INSEMINAÇÕES ARTIFICIAIS E POR RESSINCRONIZAÇÃO DA OVULAÇÃO EM VACAS BOS TAURUS INDICUS

The goals were to compare the conception rate in cows subjected to timedartificial insemination (TAI) with one AI, two AIs, or resynchronization (RES), and verify the effects of POF (preovulatory follicle) diameter on the CR. Two hundred and seventyfour cows (Bos taurus indicus) were assigned. In the group with one AI (1AIG; n=88), cows were subjected to intravaginal P4 and EB (2mg, IM) on day zero (D0); PGF2α (500μg, IM) on D7; P4 removal on D8; EB on D9; TAI and ultrasonography for POF diameter measurement on D10; PD (pregnancy diagnosis) and natural service on D41; bull removal on D90; and final PD on D110. The same protocol was used in the two AI (2AIG; n=88), except a second AI 20h after the first AI. The resynchronization group (RESG; n=98) was subjected to the same protocol as 1AIG, except a PD was performed on D40, and the non-pregnant cows received the P4 device and EB; PGF2α on D47; P4 removal on D48; EB was administered on D49; TAI was performed on D50; PD was performed, and bulls were introduced on D80; bulls’ removal on D110; final PD on D160. CR of 50, 58, and 73.4% were observed in 1AIG, 2AIG, and RESG, respectively, increasing to 85.2, 88.6, and 87.7% after natural service. The POF diameter at the first TAI was 12.8, 12.1, and 12.7mm in 1AIG, 2AIG, and RESG, respectively, and 12.6mm in RESG and 13.6mm in 2AIG (P=0.031) at the second AI. Groups 1 and 02 inseminations remained with bulls for 49 days and resynchronization for 30 days. In conclusion, RESG yielded a higher CR than TAI with one or two AIs. AI with follicles larger than 12.1mm resulted in a higher CR.Os objetivos foram comparar a taxa de prenhez (TP) em vacas Bos taurusindicus submetidas à IATF com uma IA, duas IA ou ressincronização e verificar os efeitos do diâmetro do folículo pré-ovulatório sobre a taxa de prenhez. Foram utilizadas 274 vacas (Bos taurus indicus). No grupo uma inseminação (1AIG; n=88), as vacas foram submetidas a inserção de progesterona intravaginal e benzoato de estradiol (im) no dia zero (D0); prostaglandina F2α no dia 7 (D7); remoção da progesterona em D8; administração de benzoato em D9. A IATF e a ultrassonografia ovariana foram feitas no dia 10 (D10). O diagnóstico de prenhez e a colocação das vacas com os touros ocorreu no D41; a remoção dos touros no D90; e o diagnostico final no D110. Idêntico protocolo foi usado no grupo 2 inseminações (2AIG; n=88), exceto uma segunda inseminação 20 horas após a primeira. O grupo ressincronização (RESG; n=98) foi submetido ao mesmoprotocolo que 1AIG, exceto que o diagnóstico de prenhez foi feito em D40, e as vacas não-prenhes receberam o dispositivo com P4 e benzoato neste dia, PGF2α no D47; remoção da P4 no D48 e benzoato no D49. A IA foi feita no D50; o diagnóstico de gestação e os touros foram colocados no D80; remoção dos touros no D110; diagnostico final no D160. A taxa de prenhez observada foi de 50, 58, e 73.4% no 1AIG, 2AIG, e RESG, respectivamente, atingindo 85.2, 88.6, e 87.7% após a monta natural. O diâmetro do folículo pré-ovulatório após a primeira IA foi de 12.8, 12.1, e 12.7mm no 1AIG, 2AIG, e RESG,  respectivamente, e de 12.6mm no RESG e 13.6mm no 2AIG (P=0.031) após a 2ª. IA. Os grupos 1 e 02 inseminações permaneceram com touros por 49 dias e o ressincronização 30 dias. Em conclusão, a ressincronização resultou em maior taxa de prenhez que os protocolos de IATF com uma ou com duas IAs; a inseminação artificial executada perante folículos maiores que 12,1mm resultou em maiores taxas de prenhez

The effects of intramuscular or intravenous injections of gonadotropin releasing hormone at fixed-time artificial insemination on pregnancy rates of Bos indicus beef cows

The effect of an intramuscular versus intravenous administration of gonadotropin releasing hormone (GnRH) at fixed-time AI (FTAI) on the pregnancy rates of crossbred Bos indicus beef cows was evaluated. Pluriparous nursing calv cows (n=120) were synchronized as follows: d 0 cows received a 2.0 mg injection of estradiol benzoate (EB) and insertion of a controlled intravaginal progesterone releasing device containing 0.558 g of progesterone, d 8 removal of the progesterone device , a 0.15 mg injection of prostaglandin F2α (PGF), a 1.0 mg injection of EB, and 400 IU injection of equine chorionic gonadotropin. Fifty-four hr after PGF, all cows were exposed to FTAI and a 0.084 mg injection of GnRH was administered either via Vena caudalis (n=60), or via Longissimus dorsi (n=60). Cows were inseminated with the same sire and by a single AI technician. Pregnancy was determined by the transrectal ultrasonography on d 40 after AI. Cows receiving the intravenous administration of GnRH had higher (P = 0.04) pregnancy rates than the cows receiving the intramuscular injection of GnRH (65 vs 46.6%, respectively). It was concluded that the intravenous administration of GnRH at the time of AI improved the pregnancy rates of crossbred Bos indicus beef cows submitted to FTAI