Production Losses From an Endemic Animal Disease: Porcine Reproductive and Respiratory Syndrome (PRRS) in Selected Midwest US Sow Farms

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is an endemic disease causing important economic losses to the US swine industry. The complex epidemiology of the disease, along with the diverse clinical outputs observed in different types of infected farms, have hampered efforts to quantify PRRS' impact on production over time. We measured the impact of PRRS on the production of weaned pigs using a log-linear fixed effects model to evaluate longitudinal data collected from 16 sow farms belonging to a specific firm. We measured seven additional indicators of farm performance to gain insight into disease dynamics. We used pre-outbreak longitudinal data to establish a baseline that was then used to estimate the decrease in production. A significant rise of abortions in the week before the outbreak was reported was the strongest signal of PRRSV activity. In addition, production declined slightly one week before the outbreak and then fell markedly until weeks 5 and 6 post-outbreak. Recovery was not monotonic, cycling gently around a rising trend. At the end of the study period (35 weeks post-outbreak), neither the production of weaned pigs nor any of the performance indicators had fully recovered to baseline levels. This result suggests PRSS outbreaks may last longer than has been found in most other studies. We assessed PRRS' effect on farm efficiency as measured by changes in sow production of weaned pigs per year. We translated production losses into revenue losses assuming an average market price of $45.2/weaned pig. We estimate that the average PRSS outbreak reduced production by approximately 7.4%, relative to annual output in the absence of an outbreak. PRRS reduced production by 1.92 weaned pigs per sow when adjusted to an annual basis. This decrease is substantially larger than the 1.44 decrease of weaned pigs per sow/year reported elsewhere.

Keywords: Endemic Animal Disease; Fixed effects model; Porcine Reproductive and Respiratory Syndrome; Production Impacts; Sow Farms; US Swine Industry.

Figure 1

Number of sows and weaned pigs in sixteen farms affected by porcine reproductive and respiratory syndrome (PRRS) through the pre-outbreak period. Boxes indicate the first and third percentile and middle bars represent the median.

Figure 2

Weekly average (red lines) and observed (dots) number of weaned pigs and the seven additional performance indicators during pre- and post-outbreak period.

Figure 3

Means of fitted number (log) of weaned pigs during pre- and post-outbreak period (Table S2). The horizontal dotted line shows the estimated overall baseline of production (Table 1). The smooth blue line shows a 4th degree polynomial function that fits estimated means of number (log) of weaned pigs each week during the post-outbreak period (t to t + 35). Vertical lines indicate 95% confidence intervals.

Figure 4

Means of fitted numbers (log) of the seven performance indicators during pre- and post-outbreak period (Table S2). The horizontal dotted lines show the estimated baselines of each indicator (Table 1). The smooth blue lines show a 4th degree polynomial function that fits estimated means number (log) for each indicator during the post-outbreak period (t to t + 35). Vertical lines indicate 95% confidence intervals.