The objectives of this study were to determine estrus (ER), conception (CR) and pregnancy rate (PR) of dairy cows after synchronization of estrus and the relationship between synchronization method and vaginal electrical resistance (VER). A total of 52 Holstein Friesian (HF) females were synchronized with Select-Synch or Select-Synch + CIDR protocols. Results showed that the overall ER, CR and PR were 67.30, 55.90 and 37.00 %, respectively. Mean ER was significantly (P < 0.05) higher for Select-Synch + CIDR treatment compared to Select-Synch alone (80.80% versus 53.90 %). Mean PR was higher for Select-Synch + CIDR compared to Select-Synch (46.30% versus 28.00%; P<0.05). The difference in CR between the two treatments was not significant. Cycling females had significantly higher ER (89.70% versus 39.13%; P<0.05) and PR (57.14% versus 13.04%; P < 0.05) compared to non cycling females. The interval from PGF2α injection to onset of estrus was not significantly (P < 0.05) influenced by synchronization methods and ovarian status. Duration of estrus was significantly higher for cycling females compared to noncycling females. Mean VER was significantly (P < 0.05) higher for females synchronized with Select-Synch compared to Select-Synch + CIDR. Mean VER was significantly highest at Day 0 (106.64±1.90) and lowest (84.20±0.90 ohm) at the time of the onset of estrus in both synchronization methods. Mean Diameter of Largest Follicle (DLF) was significantly higher for cycling females compared to non cycling one (12.4±0.30 versus 11.6±0.50 ohm). The inclusion of CIDR in the Select-Synch estrus synchronization protocol significantly improved ER and PR but CR was not significantly different from Select-Synch protocol. VER may be useful for improving accuracy of estrus detection during artificial insemination program.
