Impact of endemic and epidemic pathogens in performance of growing pigs

Impact of endemic and epidemic pathogens in performance of growing pigs

The risk of introduction of high impact exotic diseases in the United States requires a lot of attention, however the economic burden that endemic diseases cause to swine producers represent a much more immediate problem for the industry.

Despite the efforts invested on the control of endemic diseases in the U.S. swine industry, quantification of their financial impact throughout the production chain is often hampered by the lack of data or data analysis capabilities. Full quantification of the impact of endemic diseases present at different levels throughout the stages of the production system (piglets, nursery pigs, growing pigs, fattening pigs and sows) is often challenging due to the difficulties to compare the performance of affected herds to a valid standard.

In the case of assessing the cost of exotic diseases an option is to compare the production before and after the new pathogen is identified. In the case of endemic diseases it is often difficult to assure that the pathogen is not present unless exhaustive monitoring programs are in place (something that is usually not the case). Moreover, when both epidemic and endemic diseases are present there are many other factors that can modulate the impact that a pathogen exerts on a population, being difficult to extrapolate the finding to other systems. Still, several studies have evaluated the effect of disease in sow farms, thus providing some background information for decision makers to assess the situation in their farms and choose the most cost-effective control strategy for them.

However, there are important knowledge gaps regarding the full impact of endemic and epidemic diseases in growing pigs. The increasing use of swine management software in fattening farms provides a useful source of data that combined with results from monitoring programs already implemented in a system (even in another site located upstream in the production flow) could help to assess the impact of endemic and epidemic diseases over time.

Aid decision process

Two different projects performed at the University of Minnesota have explored this hypothesis, namely that the analysis of production records routinely collected in growing pigs together with laboratory and clinical information on the presence of selected endemic pathogens in sow and growing pig farms can help to fully evaluate their production impact. The information then can help aid the decision-process with regards to the implementation of control/eradication strategies. These two projects focused on three diseases with different epidemiological and economic implications.

  • Porcine epidemic diarrhea virus, first diagnosed in the United States in 2013 causing significant economic losses, and that had been considered an exotic disease until then.
  • Porcine reproductive and respiratory syndrome, arguably one of the most important diseases affecting the swine industry worldwide causing losses worth several hundreds of million dollars every year in the United States only.
  • Influenza A virus, one of the most common respiratory pathogens affecting swine in large parts of the world and endemic in North America, where infection occurs throughout the year.

Both projects focused on the analysis of routinely collected close-out performance records from wean-to-finish and nursery sites in which the presence of at least one of these three diseases was monitored routinely in the sow herd. Groups of weaned pigs were classified as exposed to the causative agents (weaned when there was clinical disease or the virus was detected by PCR testing on oral fluids collected in the sow farm) or non-exposed (negative results in the PCR and lack of clinical signs in the sow farm). Then, values of performance indicators such as average daily gain, average daily feed intake, feed conversion ratio and post-weaning mortality, recorded during the growing period in batches of exposed and non-exposed piglets at weaning were compared using statistical models that allowed to account for the effect of other factors that could likely impact those parameters (such as the time of the year in which animals were weaned, the number of days in feed or the flow from which they originated).

Detection of any of the three pathogens in pigs at weaning resulted in poorer performance of the pigs throughout the growing stage. Specifically, an average increase of 11% post-weaning mortality, and decreased ADG and increased FCR was observed in the first batches weaned after PEDV was detected in a farm (Figure 1). This demonstrates that PEDV infection, in addition to causing increased mortality in suckling pigs, also results in poorer performance of the surviving pigs.Presence of Influenza A virus and PRRS virus in groups of pigs at weaning was also associated with an increase in post-weaning mortality (median increase of 13% and 34% over the system-specific baseline mortality, what would translate into a raw increase of 0.65% and 1.7%, respectively), thus suggesting that early exposure to these pathogens could affect the pigs’ survival throughout the growing period.

Overall, our results demonstrate that the combination of information from surveillance protocols in sow farms and production records in growing pigs can help to quantify the full impact of endemic and epidemic diseases beyond the breeding herd. Specifically, we found an increase in post-weaning mortality associated with exposure to PEDV, IAV and PRRSV in the sow farm, and a decrease in the performance (ADG, FC) in the case of the PEDV, while this effect could not be analyzed for the other two viruses.  

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