THE EFFECTS OF DAILY EXPOSURE TO ESTROUS OR ANESTROUS 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 wit h stimulus animals (control); (2) daily exposure to an anoestrous gilt ; (3) daily exposure to an oestrous gilt; (4) daily exposure to an ano estrous sow; (5) daily exposure to an oestrous sow. All treatments wer e imposed for 20 min daily from a mean gilt age of 159 days for 100 da ys. Fourteen ovariectomised female pigs were used to provide the treat ments, 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 wit h two daily injections of oestradiol benzoate (OB) to induce oestrus, oestrus being taken as days 4 and 5 following the first injection. Ano estrous females were selected from within the same group, but females that had been treated with the OB were not used from the day of inject ion for at least 10 days. Results show that a significantly higher pro portion of gilts reached puberty within the experimental period when g iven 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 < 0.0 5) 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 expos ure to small stimulus females. The sexual status of the exposure femal e exerted no influence on the timing of gilt puberty (mean age at pube rty 210.3 vs. 207.7 days and proportion pubertal within the experiment al period 0.82 vs. 0.85 for treatments involving exposure to anoestrou s and oestrous females respectively). These data indicate that exposur e to 'strange' females can induce early puberty in the gilt. They furt her suggest that differences in the stimulus value to prepubertal gilt s of exposure to 'strange' female pigs may occur, and that any differe nces that do occur are likely to be due to the size, rather than the s exual status, of the exposure female.