Trends in the U.S. swine industry show that over the years, there has been an increase in improved producer efficacy and the appearance of fewer but larger pig farms. These changes are reflected in larger litter sizes, increased numbers of market pigs and pork production per breeding animal, and slaughter weights. These modern intensive pork-production systems, however, may pose new challenges in disease-outbreak controls. When a foreign animal disease (such as foot-and-mouth disease or classical swine fever) emerges, countermeasures must be implemented immediately. One of the control strategies is movement restriction, in which the movement of live pigs, pork products, vehicles and people is halted. Movement restriction is an essential measure to stop diseases from spreading and preventing a lengthy epidemic. However, discontinuation of these routine movements can quickly lead to adverse animal-welfare conditions, such as overcrowding among finishing pigs and feed interruptions. In fact, historical foreign animal disease outbreaks have shown that the number of healthy pigs euthanized due to adverse animal-welfare conditions often exceeded the number of pigs euthanized due to infections. For example, during the 1997–1998 classical swine fever outbreaks in Europe, the pigs that were euthanized due to adverse animal-welfare conditions comprised 62% ̶ 87% of all pigs euthanized, and their associated costs comprised more than 50% of the total direct costs of the overall outbreak-control initiative (Edwards et al., 2000; Terpstra and de Smit, 2000).
Despite its importance, very few studies have attempted to quantify the impacts of movement restrictions on the well-being of pigs during a foreign animal disease outbreak (Bargen and Whiting, 2002). Therefore, our team initiated a series of studies to quantitatively assess the impacts of movement restrictions on associated animal welfare outcomes. In this paper, we reported one of the studies with the specific objectives of (a) establishing a conceptual framework for the development of novel risk assessment models; (b) collecting available data to build model algorithms; and (c) using these models to evaluate different movement-control policies for foreign animal disease-outbreak management. Our goal was to compile and use routinely collected surveillance data on the U.S. swine industry to develop models that can promptly generate important outbreak-related information (for example, how long an outbreak might last and how many swine premises might be affected). The use of available data allows different users to easily update the models with the latest information (for example, where an outbreak starts and the ages of pigs on a farm when an outbreak starts) or to adapt the models to fit specific needs. Prompt and accurate outbreak-related information is essential for pork producers to make evidence-based decisions so the potential losses due to an outbreak may be reduced.
In this study, we used classical swine fever as a disease-outbreak model and the data on the swine industry in Indiana to develop the models. We conducted a focus group discussion among experts in pork production, epidemiology, and animal welfare, and swine veterinarians to establish a conceptual framework. We decided to focus on the two adverse animal-welfare consequences of movement restriction—namely, overcrowding and feed interruption. In addition, we decided to evaluate two movement-control policies for disease outbreak management: complete movement restriction and controlled movement. On-farm euthanasia was the only mitigation option that was used to alleviate adverse animal-welfare conditions under the complete movement restriction policy, whereas under the controlled movement policy, market-age pigs were allowed to be moved to slaughter plants after a pre-movement inspection. We used this conceptual framework and the collected data to build the models.
Our study revealed that overcrowding and feed interruption could occur within swine premises under movement restrictions very quickly (< 2 weeks) after an outbreak started. The adverse animal-welfare conditions, on average, were predicted to occur faster in nursery operations than in finisher operations. Our models also supported the implementation of the controlled movement of market-age pigs to slaughter plants as a low-risk alternative to complete movement restriction, in which on-farm euthanasia would be used as the only mitigation strategy for alleviating adverse animal-welfare conditions. Allowing healthy pigs on the premises under movement restrictions to be shipped to slaughter plants may greatly reduce economic losses; our models estimated that this controlled movement strategy could be used to alleviate adverse animal-welfare conditions on about 67% of the premises that encountered problems.