Do early life experiences influence ear necrosis development in weaned pigs?

Ear necrosis is a welfare concern in weaned pigs but there is poor understanding of the causes and risk factors, including the role of potentially stressful management practices such as handling and mixing. The study investigated the effect of frequent handling prior to weaning and mixing at weaning on ear necrosis development up to 43 days postweaning. The early life stress associated with handling, and ear scratches associated with mixing aggression were hypothesised to increase the risk of ear necrosis. At farrowing, litters (N = 37) were randomly assigned to either a Control (n = 18; 239 piglets) or Handled (n = 19; 271 piglets) treatment. Control piglets were handled 3 times from birth to weaning for routine weighing and processing procedures, whereas Handled piglets were weighed an additional 5 times during the same period. At 28 days of age, pigs were weaned into 36 mixed-sex pens as either Un-mixed (litter groups; n = 18 206 pigs) or Mixed (housed with pigs from multiple litters; n = 18 204 pigs). Preweaning, diarrhoea scores and faecal cortisol levels were assessed. Ear scratches were counted at 24 h postweaning, and ear necrosis was scored weekly from 0 (none) to 5 (substantial degradation and loss of the ear pinna). Pre- and postweaning growth was measured. Handling resulted in higher diarrhoea scores preweaning and a higher prevalence of mild ear necrosis postweaning, but there was no difference in faecal cortisol levels, moderate to severe ear necrosis, or tail lesions. Although Mixed pigs had a greater number of ear scratches, there was a higher prevalence of ear necrosis in the Un-mixed group. At the individual pig level, and irrespective of treatment, ear scratches at weaning were not associated with subsequent ear necrosis. While neither the preweaning nor postweaning treatments impacted growth, pigs with ear necrosis had lower average daily gain than pigs without. In conclusion, results suggest that scratches caused by weaning aggression do not play a role in the aetiology of ear necrosis. Although handling led to more pigs affected with mild ear necrosis, multiple factors are likely to play a role in overall ear necrosis development and its progression to moderate and severe scores.