Relação entre o diâmetro folicular, momento da ovulação e taxa de prenhez de bovinos submetidos a protocolo de IATF convencional ou em blocos

Abstract

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<0.0001). The study 2 was performed to evaluate the relationship between FS, luteal size and pregnancy rate. Artificial insemination (AI) was performed in 30 dairy cows of ECP group on study 1 and 83 beef cows synchronized as described for EB group. Data of ultrasonography evaluations at AI and 7 and 30 days after AI were used. Cows with FS > 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.