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To determine the effect of group composition on backtest responses, and to determine the predictive value of the backtest for the physiological stress response to weaning and mixing, the immunological response to ADV vaccination and the susceptibility for salmonella, 883 pigs were backtested at 3, 10 and 17 days of age. At 3 days, groups were formed according to backtest responses of animals with high responses (HR) only, low responses (LR) only, or mixed groups of animals with high, intermediate and low responses (MISC). Original litters (OR, no cross-fostering) were used as controls. Cortisol responses were measured in saliva in 173 pigs after weaning at 4 weeks of age and in 134 pigs after moving and mixing at 9 weeks of age. ADV specific immunoglobulin (Ig) titers were determined in 216 piglets from vaccinated sows and in 128 fattening pigs after vaccination. In 99 slaughter pigs, salmonella specific antibodies were determined.

In HR groups, mean backtest responses decreased after cross-fostering while in LR groups, mean backtest scores increased. In both groups, backtest responses of individual animals before and after cross-fostering were not correlated. In MISC and OR groups, all backtest scores were correlated. Weaning and mixing caused a significant rise in cortisol in all animals, while moving or weighing did not. No relations were found between backtest scores and cortisol levels. Animals with higher ADV specific Ig titers had a lower slaughter weight, but no relations with backtest or cortisol was found. Mixing (OR=3.91, P<0.10) and cortisol levels at 9 weeks (OR=2.87, P<0.10) seemed risk factors for salmonella infection, while high backtest scores (OR=0.50, P<0.05) and a higher weight at 9 weeks (OR=0.80, P<0.05) were preventive factors.

We conclude that backtest behaviour can change according to the social environment between 3 and 10 days. This could be intentional, to form a varied group, or it might be caused by a change in HPA function due to social stress. Stress factors and stress coping can influence susceptibility for certain pathogens. (Download PDF)    (Export to EndNotes)