Four estrous beagles were inseminated with 1 x 10(8) sperm into both the right and left uterine horns, and the uterine horn and oviduct on one side were removed under anesthesia after 7 hr and 24 hr, respectively. The lumen of the uterine horns and oviducts was flushed with canine capacitation medium (CCM), and movement of the sperm in CCM was assessed by phase-contrast microscopy. In a second experiment, ejaculated sperm obtained from 5 normal beagles was incubated in CCM supplemented with oviductal flush fluid (OF-CCM) at 38 degrees C with 5% CO2 in air. Motility of sperm, and percentages of hyperactivated sperm (%HA) and acrosome-reacted sperm (%AR) among freely swimming (FS) sperm were investigated until 24 hr after the start of incubation. After 7 hr of incubation the sperm was coincubated with canine oocytes in OF-CCM for 2 hr, and the number of zona pellucida-binding (zona-binding) sperm was then counted. The %HA among the sperm in the oviductal flush fluid both 7 hr (mean +/- S.E.; 15.0 +/- 2.4%) and 24 hr (77.5 +/- 5.2%) after intrauterine insemination were significantly higher than in the uterine flush fluid (P < 0.05, 0.01, respectively). The motility and %HA among FS-sperm in OF-CCM were higher than in the control medium without oviductal fluid. However, there was no difference in the %AR between OF-CCM and control medium. The number of zona-binding sperm in OF-CCM (8 +/- 1) was significantly greater than in control medium (5 +/- 1) (P < 0.05). These results suggest that oviductal fluid in the estrous bitch maintains sperm motility and induces sperm capacitation.