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.

A field trial on the effect of cross-fostering on performance, clinical health and antibiotic usage during the suckling period of pigs.

Cross-fostering is a common nursing strategy in pig production, but there is sparse evidence on its effect on antibiotic usage and disease occurrence in piglets. The objective of this study was to compare the effect of two nursing strategies on antibiotic usage, disease occurrence, weight gain and mortality in piglets. A 2×2 randomized factorial experiment was conducted in three Danish commercial pig production herds. The factors were nursing strategy (cross-fostering allowed (CF) vs. cross-fostering not allowed after initial litter equalisation (non-CF)) and weaning age (four vs. five weeks). In CF litters, the herd's usual cross-fostering strategy was applied. Piglets were followed individually from birth until weaning. Data was collected on antibiotic usage, mortality, weight gain and clinical disease. Only individual antibiotic treatments were allowed. At litter level, the effect of nursing strategy (CF vs. non-CF) on average daily gain, mortality, antibiotic treatment, clinical disease, face wounds and carpal wounds was analysed. In total, 241 litters were used for the data analysis. Approximately 30% of the CF litters were cross-fostered (either given a nurse sow, mingled with non-siblings or both) during the nursing period. The odds for antibiotic treatment during the suckling period were 1.58 times higher for CF litters compared to non-CF litters (P < 0.001). Across experimental groups, 60.8% of antibiotic treatments were administered for leg diseases. In CF litters, 15.7-21.3% of the antibiotic treatments were directed against diarrhoea, whereas in non-CF litters this was the case for less than 1%. In CF litters, the odds for carpal wounds were 1.40 times higher than in non-CF litters (P = 0.005). There was a tendency towards a higher occurrence of face wounds (OR = 1.30, P = 0.095) and clinical disease (OR = 1.25, P = 0.059) at weaning in CF litters compared to non-CF litters. There was no difference in average daily gain and mortality from birth to weaning between CF and non-CF litters. The results show that cross-fostering increases antibiotic usage in piglets during the nursing period and tends to affect the clinical health at weaning negatively.

Antibiotic and medical zinc oxide usage in Danish conventional and welfare-label pig herds in 2016-2018.

This register-based study compared the usage of antibiotics and medical zinc oxide (ZnOmed) in three different pig production systems: organic, conventional free-range and conventional indoor in 2016-2018. ZnOmed is used to prevent weaning diarrhoea with a dosage of max 2500 mg zinc/kg feed for 14 days post weaning. The treatment incidence (TI) of antibiotics (injectable and oral) and ZnOmed was calculated as the total number of animal daily doses (ADD) per 100 animals per day at herd level over a calendar year. Zero-inflated negative binomial models were used to compare the antibiotic and ZnOmed usage across the three production systems. The correlation between antibiotic and ZnOmed usage was evaluated using Spearman's correlation coefficient. In all age groups, the antibiotic TI was highest in the conventional indoor system, lower in the conventional free-range system and lowest in the organic system. In weaners, which is the age group with the highest antibiotic usage, conventional indoor, conventional free-range and organic herds had an average TI of 7.20, 3.37 and 0,48 ADD/100 animals/day, respectively. Another important finding in the study was that non-use of antibiotics is more common (>30% of herds) in welfare-label production systems (organic and conventional free-range) than in conventional indoor production (16% of herds). The overall differences in usage of ZnOmed between the three production systems were not statistically significant, but the probability of not using ZnOmed, was significantly higher for organic (36%) and conventional free-range herds (61%) compared to conventional indoor herds (19%). There was a weak to moderate positive correlation between antibiotic and ZnOmed usage at herd level with the weakest correlation in conventional indoor herds (0.31). The results indicate that ZnOmed does not appear to replace or prevent the use of antibiotics and suggest that ZnOmed is used differently in different systems. A weak correlation between the usage of antibiotics and ZnOmed in conventional indoor herds could reflect a frequent use of routine treatments within this system. The lower level of antibiotic usage in welfare-label systems indicates that a significant reduction in antibiotic use in pig production would require housing and management changes or regulatory changes in the conventional indoor system. The large variation in both antibiotic and ZnOmed usage between herds in similar production systems indicates that a further reduction in use of antibiotics and ZnOmed is achievable.