Research from Oregon State University indicates aggressive cows have lower reproduction rates than calm cows and that acclimating heifers to low-stress handling can benefit fertility. The researchers conducted two experiments. In one, they evaluated 433 Angus-Hereford cross females using chute behavior scores and chute exit velocity and rated them for temperament. Aggressive cows had a pregnancy rate of 89 percent and a calving rate of 85 percent compared with 95 percent and 92 percent, respectively, for calm cows. Individual calf weaning weights were similar for each group, but because of the higher calving rate, calm cows produced an average of 35 pounds more calf weight per cow exposed. In the second experiment, the researchers sorted 88 Angus-Hereford cross heifers, averaging 206 days of age, into two groups. One group received no acclimation and remained on pasture through the test period, while the other group was acclimated by processing them through a handling facility three times per week for four weeks. The first week, the researchers simply walked the heifers through the processing facility. The next week they restrained them in a chute for five seconds, and the restraint time increased to 30 seconds in the following weeks. Two hundred days after initiating the trial, average daily gains were similar for the two groups, but the researchers found the acclimated heifers had lower chute velocity scores and 60 percent of them had reached puberty compared with 38 percent of the control heifers. In a commercial setting, producers are unlikely to use an acclimation process as extensive as this trial, but the results suggest some acclimation could provide benefits. Based on the two trials, the researchers conclude that beef cows with aggressive temperament have impaired reproductive performance compared with cohorts with adequate temperament, and acclimation to human handling after weaning hastens reproductive development of replacement heifers.