A field trial on the effect of cross-fostering and weaning age on daily gain and disease resilience in weaned pigs.

Alternative management strategies that can increase disease resilience and reduce antibiotics in weaned pigs are needed. Our objective was to compare the effect of two nursing strategies and weaning ages on weight gain, clinical health and antibiotic treatments in weaned pigs not provided with medical zinc oxide in feed. A 2×2 factorial trial was conducted in three Danish commercial herds. Nursing strategies tested were "cross-fostering allowed" (CF) vs. "cross-fostering not allowed" (non-CF). Weaning ages tested were four (24-29 days) vs. five weeks (31-35 days). Pigs were followed from weaning until 33-35 days post-weaning. Herd staff made decisions on and registered antibiotic treatment, removal of pigs to sick pens and mortality. Pigs were weighed at weaning (N = 3139) and on day 33-35 post-weaning (N = 2898). Clinical examinations were carried out on day 4, 7 and 33-35 post-weaning. The effect of nursing strategy and weaning age on weight gain, clinical health and antibiotic treatments was analysed by mixed linear and logistic models. We found that pigs weaned at five weeks of age gained 103.6 g more daily compared to pigs weaned at four weeks during the 33-35 days post-weaning (<0.001). Weaning age affected diarrhoea prevalence, but the effect differed between herds. For pigs weaned at five weeks compared to four weeks of age, the odds for diarrhoea one week post-weaning was 0.7 times lower in one herd whereas the odds for diarrhoea were 2.0 and 1.4 times higher in the two other herds, respectively (P < 0.05). In all herds, we found fewer runted (OR=0.28, P < 0.001) and thin (OR=0.23, P < 0.001) pigs 33-35 days post-weaning in pigs weaned at five weeks of age compared to four weeks. Furthermore, in all herds, CF pigs were more likely to be removed to a sick pen or to die. In total, 5.9%, 13.6% and 64.9% of the studied weaned pigs were treated with antibiotics in the three herds, respectively. Treatment prevalence did not associate to weaning age or nursing strategy and did not in all cases appear to be linked with diarrhoea prevalence. The results indicate that a higher weaning age and less cross-fostering to some extend increase disease resilience post-weaning but herd specific factors interacted with the effects. The prevalence of pigs treated with antibiotics were herd dependent and may relate more to management decisions than to disease level.