Boar-induced puberty in gilts handled pleasantly or unpleasantly during rearing

Abstract

The effect of handling during rearing on attainment of puberty in response to daily exposure to a mature boar was studied using 70 gilts. The gilts were either handled pleasantly (patted and stroked) or unpleasantly (given a brief electric shock) when they approached the experimenter during handling sessions which were imposed for 3 min, 3 days per week for 12 weeks from 80 to 164 days of age. In a 3-min behavioural test at 164 days of age, pleasantly handled gilts were quicker to approach within 0.5 m of the experimenter ( P < 0.01), spent more time within 0.5m ( P < 0.05) and interacted more quickly ( P < 0.01) and more frequently ( P < 0.05) than gilts handled unpleasantly. There was no difference between treatment groups in growth rate or in the overall proportion of gilts which attained puberty but the mean interval from first boar exposure to puberty was shorter for unpleasantly handled gilts (20.6 vs. 27.3 days, P < 0.05). At 10, 15 and 20 days after first boar exposure, significantly more unpleasantly handled gilts had reached puberty than had pleasantly handled gilts ( P < 0.05). The ratio of the cross-sectional area of the adrenal cortex to the adrenal medulla was not affected by handling treatment (3.41 ± 0.24 vs. 3.57 ± 0.27 for pleasantly and unpleasantly handled gilts, respectively). We conclude that the unpleasantly handled gilts were not chronically stressed but were more sensitive to acute stress making them more, not less, responsive to puberty stimulation by a boar. The data also suggest that grouped gilts respond differently to gilts housed alone and that fear of humans is not necesarily indicative of chronic stress in the gilt.