Relationship between follicular size, ovulation time and pregnancy rate of cattle submitted to conventional or in block FTAI

The aim of study 1 was to evaluate the relationship between follicular size (FS) and moment of ovulation in Bos taurus cows. Data of 138 cows from 4 protocol of estrus synchronization were used. Cows received an intravaginal progesterone-releasing device plus 2 mg of Estradiol Benzoate (EB) on D0. On D8, device was removed and cows were randomized in four groups: Estradiol cipionate (ECP, n=76), administrated 48 hours after device removal; EB (n=19) administrated after 24 hours; GnRH (n=28) administrated after 60 hours; or Control (no inductor; n=15). Ultrasonography evaluations were performed each 12 hours after device removal to measure FS and to detect ovulation. In ECP group, cows with larger FS had earlier ovulation (R²=0.96, P 14 mm demonstrated higher pregnancy per AI (P/IA) than cows with FS <10 mm or < 11 mm (dairy and beef cows, respectively; P<0.05). The FS was correlated to luteal size (R²=0.71) and cows with larger corpus luteum had higher P/AI (P<0.05). The aim of study 3 was to evaluate serum estradiol and progesterone concentrations. Serum samples of 14 cows from Study 1 were used. Cows with larger LS had lower serum progesterone at ovulation. The aim of Experiment 2 was to evaluate whether chancing AI time according FS would improve P/AI. Dairy (n=65) and beef cows (n=90) were synchronized as described for ECP group. Beef cows received 350 IU of eCG on D8. Ultrasonography evaluation was performed at AI and cows were divided according FS in two groups (≤ 10.4 mm or ≥ 10.5 mm) and after randomized in control group (Conventional FTAI), Block 1 (≥ 10.5 mm): AI 48 hours after device removal; or Block 2 (≤ 10.4 mm): AI 65 hours after device removal. No differences were observed between Conventional and blocks FTAI. Lower pregnancy rate observed in cows with smaller follicles possibly was not attributed with asynchrony between AI and moment of ovulation.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESO objetivo do estudo 1 foi avaliar a relação do diâmetro folicular (DF) e momento da ovulação em fêmeas Bos taurus. Dados de 138 fêmeas bovinas de 4 protocolos de sincronização foram utilizados. Os animais receberam dispositivo intravaginal de progesterona (P4) e 2 mg de Benzoato de Estradiol (BE) no D0. No D8, a P4 foi retirada e as fêmeas foram divididas aleatoriamente em 4 grupos: Cipionato de Estradiol (ECP; n=76), administrado na retirada da P4; BE (n=19), administrado 24 horas após; GnRH (n=28), administrado 60 horas após; ou Controle (n=15). Foram realizadas avaliações ultrassonográficas de 12 em 12 horas a partir do D8 para a mensuração do DF e detecção da ovulação. No grupo ECP, vacas com maior DF, apresentam ovulação mais precoce (R²=0,96, P<0,0001). O estudo 2 foi realizado para avaliar relação do DF, volume do corpo lúteo (CL) e prenhez. Foi realizada inseminação artificial (IA) em 30 fêmeas leiteiras do grupo ECP do estudo 1 e em 83 fêmeas de corte sincronizadas conforme descrito no grupo BE. Dados de avaliações ultrassonográficas no momento da IA, 7 e 30 dias após a IA foram utilizados. Vacas com DF >14 mm apresentaram maior prenhez/IA (P/IA) do que vacas com DF <10mm ou < 11mm (leite e corte, respectivamente; P<0,05). O DF foi correlacionado com o volume do CL (R²=0,71) e maiores CLs apresentaram maior P/IA (P