Increasing the age of gilts at first boar contact improves the timing and synchrony of the pubertal response but does not affect potential litter size

One hundred and ninety-two Large White/Landrace crossbred gilts were used in this study. The study was conducted in two blocks, with 16 gilts allocated to each of six treatments in each block. The treatments compared the effects on puberty attainment of commencing boar exposure at 161, 182 or 203 days of age, and the effect of first mating gilts at either the pubertal or second oestrus on ovulation rate and early embryo survival. Boar contact took place in a detection-mating area (DMA), and consisted of 20 min/day of full contact with a vasectomized boar greater than ten months of age. Gilts were artificially inseminated at the allocated oestrus, with the reproductive tracts collected at 22.8 ± 0.4 days after first mating (mean ± S.E.M.), and the numbers of corpora lutea and viable embryos recorded. The age at which gilts attained puberty increased with the age at which boar exposure commenced. Mean gilt ages at puberty were 179.5 ± 1.6, 191.7 ± 1.2 and 210.3 ± 0.9 days, respectively, when boar contact commenced at 161, 182 and 203 days of age, P < 0.01. Mean days-to-puberty was significantly shorter when boar contact began at 182 and 203 days of age compared to 161 days of age (10.4 ± 1.2 and 8.3 ± 0.9 days versus 18.9 ± 1.5 days, respectively, P < 0.01). Similarly, commencing boar exposure at 182 or 203 days of age as opposed to 161 days of age significantly increased the proportion of gilts attaining puberty within 10 days of start of boar exposure (0.67 and 0.70 versus 0.24, P < 0.01). Mean days-to-puberty and the synchrony of puberty attainment were similar when boar contact commenced at 182 and 203 days of age. There was no significant effect of mating oestrus or age of gilts at mating on ovulation rate, embryo number or embryo survival. In conclusion, the current data indicate that the timing and synchrony of puberty attainment is significantly improved when first boar exposure of gilts is delayed until 182 days of age. Further, it is evident that within the age range investigated, delaying first mating until the second oestrus does not significantly increase either ovulation rate or embryo number at day 20 post-mating.