The estrus cycle was synchronized at vaccination and heifers were artificially inseminated 8 days (one dose) or 36 days (two dose) after initial vaccination. Pregnancy rates were greater for control heifers (90%; P = 0.02) and heifers given the inactivated virus vaccine (one dose: 86%; P = 0.08; or two: 90%; P < 0.01) than those given the MLV vaccine (48%)