THE IMPORTANCE OF FAMILIARITY WHEN GROUPING GILTS, AND THE EFFECT OF FREQUENT GROUPING DURING GESTATION

The importance of previous acquaintenceship when grouping (Study I) an d the effect of frequent grouping during gestation (Study II) on gilts were studied to further elucidate the causes and effects of aggressiv e interactions when gilts are mixed. In Study I, 2 gilt groups (gilt a ge about 7 months) were used, A (n = 6) and B (n = 8), where A and B g ilts were unacquainted with each other as they did not have any physic al, visual or olfactory contact during the growth period. Different pa irs of B gilts were mixed first with Group A for 4 days (first groupin g), returned to B for 7 days, and then regrouped with Group A (second grouping) for 1 day. Aggressive interactions on the day of grouping (d ay 0) were studied at both the first and second grouping. At the first grouping with A more aggressive interactions were noted than at the s econd one (difference of aggressive interactions different from zero, p = 0.02). Few aggressive interactions occurred on day 0 when the B pa ir was returned to B. When mixed with A, the B gilts generally kept aw ay from the A gilts, and spent more time standing than they did in the B group. In Study II for each of the 6 trials (cortisol 5 trials), 2 groups of 6 gilts (gilt age about 8 months) were established before se rvice where one group was mixed every third week during gestation (4 r egroupings) with 3 unfamiliar sows for a week: new sows were used at e ach regrouping. The ''control'' group was not regrouped. Significantly more injuries were noted on the regrouped Silts (p=0.01-0.05 one week after grouping); they also had a greater increase in blood cortisol l evels 3 hours after grouping, in comparison to those of the controls. However, the cortisol increase was only significant (p=0.05) for the f irst regrouping. No significant differences between the two groups wer e noted with respect to litter size at birth, sow morbidity before, du ring or after farrowing, or to piglet mortality and morbidity. However , the regrouped gilts tended to have more animals that did not test pr egnant at 28 days after service, more abortions, more pigs dying ante- and intrapartum, and more cases of MMA.