This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
This week we take a look at PRRS EWMA patterns in Iowa, North Carolina, Minnesota, Oklahoma, Nebraska and Illinois, thanks to research done by Mariana Kikuti, Emily Geary, Paulo Fioravante, Marcello Melini, Miranda Medrano, Cesar Corzo.
The time needed between an outbreak and consistently weaning porcine reproductive and respiratory (PRRS) virus PCR negative pigs is referred to as time-to-stability (TTS). In this analysis we describe differences in TTS according to the season when the PRRS outbreak occurred in farms located in the Midwestern United States.
161 PRRS outbreaks in 82 sow farms were classified based on the date of the outbreak:
March 21st to June 20th: Spring
June 21st to September 20th: Summer
September 21st to December 20th: Autumn
December 21st to March 20th: Winter
TTS was calculated as the time from the reported PRRS outbreak to the time of the last PRRS PCR negative result in wean-age pigs.
A significant difference was detected in TTS among seasons. The median TTS was higher in spring and summer, compared to autumn and winter.
An explanation for the observed TTS difference among seasons may be found in environmental survivability of the virus as for PRRS outbreaks that occur during spring or summer, the last phase of the stability process coincides with the arrival of winter where the reduced ventilation and decreased temperature within the farm may favor PRRS survival resulting on a lower likelihood of elimination during this time.
There is significant within farm PRRS time-to-stability variation.
Several factors contribute to PRRS time-to-stability variability; however, there is still a significant amount of unexplained variability.
The role of within farm management practices and internal biosecurity measures should be further explored.
Porcine reproductive and respiratory syndrome (PRRS) stability is reached when no evidence of infection is observed in wean-age piglets. Sample size to detect PRRS virus in wean-age piglets usually involves blood sampling of 30 piglets, at least four times, 30 days apart (Holtkamp et al., 2011). The cumulative time from the intervention (i.e. whole herd exposure, herd closure) to PRRS stability is usually referred to as time-to-stability (TTS).
Here we summarize differences in TTS in MSHMP participating farms located in the Midwest that have had at least two PRRS outbreaks.
Six systems that are similar in the way they test to classify a herd as stable were selected for inclusion in the study. PRRS outbreaks reported from 2011 to 2017 were used for analysis.
TTS was defined as the time period from the date of outbreak reporting to the date when PRRS stability was reported (last consecutive negative PCR result). To assess the variability in TTS, only farms that had at least two PRRS outbreaks were selected.
Overall, 133 PRRS outbreaks in 53 farms were recorded withtwo, three, four and five outbreaks in 35, 11, 5, 2 farms, respectively. The median TTS standard deviation of PRRS outbreaks within the same farm was 12 weeks (minimum = 0 weeks, maximum=88 weeks).
After accounting for the effect of the intervention using MLV or FVI, the RFLP pattern of the virus associated with the outbreak and previous PRRS outbreaks in the farm, the PRRS time-to-stability correlation of outbreaks in the same farm and system was only 1.2%.
In other words, TTS of two given outbreaks in the same farm were not correlated indicating that TTS within farm is highly variable.
There is a high TTS variability after a PRRS outbreak within the same farm that is not accounted for by the effect of the intervention used, the virus (i.e RFLP), previous PRRS outbreaks in the farm and system.
In this publication in Frontiers in Veterinary Science, Drs. Valdes-Donoso from UC Davis and Andres Perez from the Center of Animal Health and Food Safety (CAHFS) at the University of Minnesota, measured the impact of Porcine Reproductive and Respiratory Syndrome (PRRS) on the production of weaned pigs.
To do so, they monitored 16 different sow farms, all parts of a single production system in the Midwest for 48 weeks and recorded a total of 8 indicators:
number of weaned pigs
number of stillbirths per litter
number of live births per litter
number of pre-weaned dead
number of sows farrowing
number of sows repeating service
number of sows aborting
number of sows dead
For each farm and each indicator, the 12 weeks before the outbreak served as a baseline for the farm performances and the data was recorded until 35 weeks post outbreaks. All of the outbreaks occurred during the second half of 2014. The inventory of the farms varied between 2,714 and 6,009 breeding females.
The following figure represented the weekly average for the 8 recorded parameters from 12 weeks pre-outbreak to 35-weeks post-outbreak.
Based on these results, it was estimated that a PRRS outbreak caused a 7.4% decrease in weaned pigs per sow year, i.e., 1.92 fewer weaned pigs per breeding unit. In an average sized farm of this firm, the slight reduction in farrowing yielded a decline of 249 fewer farrows per year. The chances that a sow repeats service increased by 37%, while aborted fetuses increased by 26% in a year with a PRRS outbreak.
The primary estimate (using 12 weeks as pre-outbreak period) is that PRRS reduced weaned pig production per farm by 7.4% on an annual basis, leading to a decrease in output value per sow year of $86.6, or $367,521 per farm year for an average sized farm. If instead we assume the outbreak began in t −1 (i.e., using 11 weeks as pre-outbreak period), the estimated reduction in weaned pig production was 7.6%, or $88.8 less per sow year and an average revenue loss of $376,773 among the farms studied.
Results showed that weaned pig production declined in week t − 1, although statistically insignificant, as did several performance indicators. The data suggest that the average PRRS outbreak in this set of farms began at least one week before it was announced.”
The rise in abortions was the strongest signal of PRRSV activity in our data. Increased surveillance, particularly to rising abortions, may allow farms to identify PRRS more quickly.
The length of PRRS outbreaks, as well as their effects over time, is highly variable. The results of this study demonstrate that PRRS has a negative effect on weaned pig production for a longer time than previously estimated. Indeed, the estimated means of weaned pig production remained below the baseline throughout the 35 weeks that we are able to observe following the outbreak.
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.
Influenza is endemic and seasonal in piglets from sow farms in the Midwest with higher infections in winter and spring.
Influenza seasonality was partially explained by outdoor air absolute humidity and temperature trends.
Influenza genetic diversity was high and co-circulation of more than one genetically distinct virus was common.
To study influenza levels over time and its seasonality, monthly testing data of piglets at weaning from 34 sow farms during ~5 years were analyzed.
There were 28% of positive submissions with a median influenza herd-level prevalence of 28%. Genetic diversity was significant with 10 genetically distinct clades of contemporary US swine influenza viruses as shown below. Furthermore, 21% of farms had 3 genetically distinct viruses circulating over time; 18% had 2, 41% had 1 and 20% had no isolates available.
In summary, influenza herd-level prevalence in Midwestern sow farms had a seasonal pattern with higher levels in winter and spring. This is important to better allocate influenza control strategies such as vaccination in sow farms. Influenza seasonality was partially explained by outdoor air absolute humidity and temperature although other factors such as immunity and new introductions may play a role in the observed seasonality.