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The effectiveness of twice daily (2x) vs once daily (1x) boar exposure (BE) and the possible interaction of frequency of BE with type of BE (physical, PBE vs fence-line, FBE) was evaluated in two genetic lines of the Gene Pool population (AP, selected for early age at puberty and RLS, composite of genetic lines selected for ovulation rate or litter size) differing in average pubertal age and in RLS gilts at two different ages (130 and 154 d). Gilts from the RLS line (n=128) were allotted randomly, within litter, to once or twice daily BE, PBE or FBE and to initiation of BE starting at 130 d or 154 d. Gilts from the AP line (n=64) were allotted randomly to the same treatments except that BE was initiated at 130 d only in AP gilts. Two sets of three Gene Pool boars (16 months of age at start) were used to stimulate the gilts. Gilts were maintained in groups of eight per pen and were taken to the boar room for stimulation by boars. Duration of BE was standardized at 10 min per each exposure. Physical boar exposure induced a more rapid and more synchronous first estrous response than FBE, especially at the once daily frequency. Boar exposure was most effective at inducing a rapid and synchronous first estrous response when initiated in gilts nearing puberty, i.e., at 130 d in AP gilts and 154 d in RLS gilts. Added frequency of BE (2x vs 1x per d) tended to induce a more rapid pubertal response in gilts nearing onset of puberty (AP 130 d and RLS 154 d group), but not when gilts were in an earlier stage of pubertal development (RLS 130 d group). Proper timing of BE is essential to obtaining optimal pubertal response to BE. Physical boar exposure is required to achieve optimal pubertal responses with once daily BE but PBE and FBE produce comparable pubertal responses when provided twice daily.