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Accuracy of estrus detection in response to physical (PBE) vs fenceline (FBE) boar exposure was evaluated in 40 gilts during two successive estrous periods. Gilts heat checked with FBE expressed shorter estrous periods (.6 day) than PBE gilts. Estrus was detected within five minutes of boar exposure in 100 percent of gilts on both treatments except for PBE gilts on the first day of estrus. The first day of estrus was expressed after five minutes of boar exposure in 16.2 percent of PBE vs 0 percent of FBE gilts. The PBE gilts may be near the beginning of estrus. They are unresponsive to limited (15 min) FBE and slow to respond to PBE. Fertility was not compared in this study, but inseminations timed 12 to 24 hours after detection of estrus in these gilts (gilts not detected with FBE and slow to respond to PBE on their first day of estrus) will be too late to result in high fertility. Ovulation will occur or be in progress in these gilts at the time of insemination. Therefore, heat-detection with physical boar exposure rather than fence-line boar exposure is recommended to achieve proper timing of insemination and high fertility in gilts.