The effects of daily exposure to oestrous or anoestrous gilts and sows on the attainment of puberty in the gilt

Seventy Large White/ Landrace crossbred gilts were allocated by litter of origin and liveweight to one of five treatments: (1) no contact with stimulus animals (control); (2) daily exposure to an anoestrous gilt; (3) daily exposure to an oestrous gilt; (4) daily exposure to an anoestrous sow; (5) daily exposure to an oestrous sow. All treatments were imposed for 20 min daily from a mean gilt age of 159 days for 100 days. Fourteen ovariectomised female pigs were used to provide the treatments, seven of these being designated small (mean liveweight 78.9 ± 4.1 kg) and seven designated large (mean liveweight 192.0 ± 15.0 kg). These ovariectomised females were treated on a rotational basis with two daily injections of oestradiol benzoate (OB) to induce oestrus, oestrus being taken as days 4 and 5 following the first injection. Anoestrous females were selected from within the same group, but females that had been treated with the OB were not used from the day of injection for at least 10 days. Results show that a significantly higher proportion of gilts reached puberty within the experimental period when given daily contact with stimulus animals than when not stimulated (P < 0.05). Exposure to large stimulus females tended to reduce gilt age at puberty (204.2 vs. 216.3 days) and significantly increased (P < 0.05) the proportion of gilts attaining puberty by days 29 (0.46 vs. 0.15) to 40 (0.54 vs. 0.19) of the experimental period compared with exposure to small stimulus females. The sexual status of the exposure female exerted no influence on the timing of gilt puberty (mean age at puberty 210.3 vs. 207.7 days and proportion pubertal within the experimental period 0.82 vs. 0.85 for treatments involving exposure to anoestrous and oestrous females respectively). These data indicate that exposure to ‘strange’ females can induce early puberty in the gilt. They further suggest that differences in the stimulus value to prepubertal gilts of exposure to ‘strange’ female pigs may occur, and that any differences that do occur are likely to be due to the size, rather than the sexual status, of the exposure female.