O presente estudo objetivou avaliar o diâmetro do folículo ovariano pré-ovulatório (FPO) no momento da IATF em vacas multíparas Bos taurus indicus correlacionando-o com a taxa de concepção (TC). Foram utilizadas 145 vacas, paridas até 65 dias, e submetidas a único protocolo: no dia 0 (d0) implante de 1,0 g de progesterona + aplicação de 2,0 mg de benzoato de estradiol; em d8 remoção dos implantes e aplicação de 500 µg de D-Cloprostenol + 300 UI de Gonadotrofina coriônica equina e 1,0 mg de cipionato de estradiol; no d10 mensurou-se o FPO (ultrassom) e procedeu-se a IATF com sêmen congelado. No d35 pós IATF realizou-se o diagnóstico de prenhez. A taxa de concepção à IATF foi de 62,7% e o diâmetro médio do FPO nas vacas prenhes foi de 15,1mm, e de 13,7mm nas vazias (P=0,03). Foram estabelecidos 04 estratos relativos ao diâmetro dos FPOs (mm): 8,0 a 11,0; 11,1 a 14,0; 14,1 a 17,0 e 17,1 a 20,0, resultando respectivamente em 37,0; 75,7; 66,6 e 72,7% de TC. Estratificou-se ainda o diâmetro do FPO em £11,0 mm e ³ 11,1 resultando em TC de 36,8% e 72,0% (P < 0,01) respectivamente. Onze animais ovularam antes da IATF, com TC de 36,4%. Concluiu-se que o diâmetro do FPO na IATF tem correlação com a TC; FPOs > 11,1mm constituem forte indicativo de maior eficiência reprodutiva.

Contents The study aimed to evaluate pregnancy per artificial insemination (P/AI) of cows subjected to synchronization and resynchronization in ovulation protocols using intravaginal progesterone‐releasing insert (P4) before pregnancy diagnosis (PD) and the relationship of PR with the diameter of preovulatory follicles (ØPOF) before TAI. Cows (n = 378) were distributed into two groups: a resynchronization group with new devices (GRN; n = 185) and resynchronization group with used devices (GRU; n = 193). On Day 0, both groups received a new P4 and estradiol benzoate (EB). On D8, P4 removal + D‐cloprostenol + eCG + estradiol cypionate (EC) was done. On d10, TAI was conducted. On d32, cows were resynchronized and divided into two groups, GRN (n = 185) and GRU (n = 193). The GRN group received a new P4 + EB, and the GRU group received a used P4 + EB. On d40, the P4 was removed + PD. The non‐pregnant cows received D‐cloprostenol + eCG + EC. US was done again on d42 to determine ØPOF before the second TAI. The P/AI of the GRN and GRU groups after synchronization were 56.2% and 57.0% (p = 0.87), respectively, and those after resynchronization were 58.0% and 37.3% (p < 0.008), respectively. The P/AI of the GRN and GRU groups observed after TAI (synchronization + resynchronization) were 81.6% and 73.1%, respectively (p = 0.047). No difference (p = 0.067) in ØPOF between the pregnant and non‐pregnant cows in the GRN was found, whereas the GRU group showed a significant difference (p = 0.003). Resynchronization protocols optimized the P/AI in both groups. New intravaginal devices resulted in greater P/AI and P/AI accumulation in resynchronization as compared with the GRU; the ØPOF was related with P/AI.