The objective of this study was to identify risk and protective factors related to five major welfare indicators in pigs. The researchers selected these indicators in accordance with the Real Welfare initiative in the U.K., which aimed to provide an animal-focused approach to animal welfare. This is in contrast to traditional resource-based approaches. The indicators that the researchers used were lameness, pigs requiring hospitalization, severe tail lesions, severe body marks, and enrichment use. The researchers identified risk factors for the five indicators, identified a relationship between pen environment and the severity of each indicator, and highlighted possible protective measures that can be taken to reduce the incidence of each indicator.

Trained veterinarians from 89 different veterinary practices collected data for use in this study between April 2013 and May 2016. The farms used for sampling all belong to the Red Tractor Pigs Assurance Scheme. This is a program designed to assess pig farmers’ capability to comply with animal welfare standards. During each veterinary visit—between two and four per year—the veterinarians randomly selected several pens. At small farms, the veterinarians tested a minimum of 300 pigs per year. And at large farms, they tested at least 900 pigs. They then tested the selected pens for each welfare indicator. They noted the following variables for each pen as possible risk factors: pen size, ventilation type, weight of the pigs, feed availability and type, feeder form, and enrichment. Also, they considered tail docking and length of the pig to assess the risk of tail lesions.

Pigs were at an increased risk of lameness when housed in outdoor pens, rather than indoor pens. Also, bedding lowered lameness risk on its own, but it increased the risk when combined with objects in the pens. Pigs between 30 and 50kg (about 65-110lbs) had a lower risk of lameness when compared with pigs weighing more than 50kg (about 110lbs).

The mean number of pigs requiring hospitalization was significantly lower if they lived in outdoor pens compared to those living in indoor pens. But, pigs kept in both indoor and outdoor pens had a higher rate of hospitalization than those kept strictly in indoor pens. Small and medium sized pens, as well as those with powered ventilation, were more likely to house pigs requiring hospitalization than large pens with natural ventilation. The results also showed that bedding reduced the risk of hospitalization.

The researchers found that outdoor pens greatly reduced the risk of severe tail lesions compared to indoor pens. Also, they found that the feed type was a significant factor. There was a much lower incidence of tail lesions in pigs fed with meal compared to pigs fed with liquid or pellet feed. Large pens and the presence of bedding also reduced the risk of tail lesions. Like lameness, though, tail lesions were more common in pens with both bedding and objects. Undocked tails and a weight under 50 kilograms also reduced the risk of severe tail lesions.

The risk of severe body marks was significantly lower in outdoor pens, as well as in pens with restricted feed and natural ventilation. The risk factors for severe body marks appeared to be lower body weights, docked tails, free feeding, and powered ventilation.

Enrichment use was high in all pen types. But it was the highest in outdoor pens by a significant amount. Larger pens, as well as those with natural ventilation, meal feed, and bedding, all showed an increase in enrichment usage. Smaller pigs weighing between 30 and 50 kilograms interacted more with enrichment than larger pigs weighing over 50 kilograms did. The risk factors for low enrichment usage included liquid feed, small or medium pen sizes, and docked tails.

Overall, this study showed that outdoor pens improve all welfare outcomes of pigs, apart from lameness. Also, the study showed that the presence of bedding and meal feed had beneficial impacts on the pigs’ welfare. There is some evidence to suggest that tail docking alone does very little to prevent tail biting or injury. The researchers stress that observation and intervention are paramount in all environments. And they note that no single factor is responsible for either poor or satisfactory welfare. Larger-scale multi-variable studies will be necessary before we can establish definitive causal relationships.