The effect of duration of boar exposure on the frequency of gilts reaching first estrus.

One-hundred crossbred gilts were used in an experiment that was designed to examine the effects of duration of boar exposure on the proportion of gilts reaching first estrus. Two replicates (summer and fall) of 50 gilts each were randomly assigned, within litter, to one of the following treatments: 1) 30 min of daily boar exposure, 2) 15 min of daily boar exposure, 3) 5 min of daily boar exposure, 4) continuous fence-line boar exposure, plus walked to a neutral pen and exposed to a different boar for 10 to 15 min daily, or 5) continuous fence-line boar exposure. Boar exposure lasted for 30 d. The percentage of gilts exhibiting first estrus by 210 d of age ranged from a high of 65.0 for treatment 4 to a low of 10.0 for treatment 5. Treatments 1, 3 and 4 were greater than treatment 5 (P less than .05), but not different from treatment 2. There were no differences in average age at first estrus. Treatment means for days to puberty after boar exposure were not different (P greater than .05). However, a significant treatment X season interaction occurred. This interaction appears to suggest seasonal trends. These results indicate that treatments 1 and 4 (30 min daily and continuous fence-line boar exposure plus 10 to 15 min, respectively) were the most effective methods tested for the induction of first estrus.