Use of processing fluids and serum samples to characterize PRRSv dynamics in 3 day-old pigs

This new publication in Veterinary Microbiology describes the best methodology to monitor 3-day-old piglets for PRRS, using both serum and processing fluid samples. The first author of the publication is Dr. Carles Vilalta, member of the Morrison Swine Health Monitoring Program (MSHMP) team.

Key points

  • Processing fluids (PF) constitute a useful sample to detect PRRSV infections at processing.
  • PRRSV can circulate in the farm at a low prevalence, increasing the chances of a re-break.
  • Young parity female litters should be targeted for PRRSV detection.
  • Current practice to bleed 30 pigs could be underestimating PRRSV prevalence in the herd.
  • The decrease in sensitivity at the litter level can be compensated by sampling more litters to detect PRRSV at the herd level.


The study was conducted in a 6,000 sow farm with a PRRS stable status. Every 3 weeks, serum samples and processing fluids were collected from all piglets in 10 randomly chosen litters. This process was then repeated 8 times, meaning that the farm was monitored for a total of 24 weeks. All samples were tested via PCR. 3 samples with the lowest Ct value were tested by virus isolation and sequencing of the ORF5 gene was performed.


10.6% of the piglets tested positive for PRRSv via serum PCR, representing 29.8% of the litters. The same number of litters tested positive via processing fluid PCR testing.

The percentage of processing fluid positive samples was significantly higher is parity 1 and 2 sows compared to parity 3 and older sows. Additionally, a significant association between parity and probability of detecting a positive pig was observed.

A significant higher proportion of positive serum samples was observed in males compared to females. A similar trend was obtained when comparing positive Ct values by gender with values from males being lower (i.e., higher viral load) than those from females.

ct value processing fluids versus serum samples PRRS
Cycle threshold (Ct) positive (≤35) and suspect (between >35 and 40) value distribution for serum (S, triangle) and processing fluid (P, circle) samples overtime (2, 5, 8, 11, 14, 17, 20 and 23 weeks post outbreak). Horizontal black lines indicate the mean Ct values for each week and sample type

Using a Ct value of 37, processing fluid samples had a Se and Sp of 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%), respectively when compared with litter RT-PCR results obtained from individual serum samples. The total agreement between both tests was 92.2% and the positive and negative predictive values were 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%), respectively. False negative processing fluids were identified in litters having 2 or less PRRSV positive piglets

The agreement between the PF and serum results was kappa = 0.81 (95% CI: 0.59–1.00). The difference in the proportion of positive samples between both types of sample was not statistically significant (McNemar test, p = 1).


Collection of serum samples of pigs at weaning to monitor for porcine reproductive and respiratory syndrome virus (PRRSV) has become a common practice to determine PRRSV herd infection status. Diagnostic sensitivity of this practice is low in herds undergoing PRRSV elimination once prevalence of infection is near zero. Thus, the goal of this study was to characterize the dynamics of PRRSV infection in 3 day-old pigs overtime using serum and serosanguineous fluids obtained as part of castration and tail docking practices (processing fluids (PF)). Secondary goal was to estimate sensitivity and specificity of PF in the 3 day old population. A 6000 breed-to-wean sow herd was monitored every three weeks for 23 weeks after a PRRSV outbreak by collecting both PF and individual serum samples from all pigs in the selected litters. Out of the 77 litters tested, 23 (29.8%) were identified as positive using the PF and the serum samples, with a Cohen’s kappa statistic of 0.81 (95% CI: 0.59–1) between the results obtained in each sample type. The sensitivity and specificity of the PF relative to the results in serum was 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%) respectively. The percentage of PRRSV positive litters decreased over time and litters from gilts were more likely to test positive than those from older sows. Overall, the study demonstrates that PF can be a convenient and reliable specimen to monitor PRRSV infection in breeding herds.

Follow the link to read the entire article.

Science Page: Quarterly review of MSHMP reported PRRSv Restriction Fragment Length Polymorphism (RFLP) patterns

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 are sharing a report from the MSHMP team regarding reported PRRS RFLP patterns.


  •  Recording PRRSv RFLP and sequences will provide better insights into the epidemiology of the disease at local, state and national level.
  • Building a RFLP database will allow us to assess which factors could be involved or related with the emergence of a new RFLP.
  • The predominant pattern RFLP in this quarterly review is the 1-7-4.

In the first quarter of the 2018/2019 incidence year, 20 breaks affecting 12 production systems were reported. Out of these, 4 occurred in July, 13 in August and 3 in September.

Of those 20 farms, three had a break while still being status 1, one was status 2 in the process of eliminating the disease (not using any immunization protocol at that point), 6 were using field virus as the acclimatization protocol (2fvi), 8 were using vaccine (2vx), one was provisionally negative (status 3) and one broke from a status 4 after being almost 4 years completely negative (see figure below).

RFLP patterns with status at break

The distribution of the breaks is wide and affects different states. Thus, we had 6, 1, 4, 1, 4, 2, 1 and 1 break in the states of IA, IN, MN, MO, NC, NE, OK and PA, respectively. The closest 2 farms that broke were 1.2 miles apart, belonged to the same company and had the break a week from each other (no sequences was provided).

Eight out of the 20 breaks reported were accompanied by the associated RFLP. The predominant (4 out of 8) RFLP pattern since July is 1-7-4. Iowa was the state with the highest number of 1-7-4 cases.

Science Page: African swine fever experience in a large commercial system in the Russian Federation

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 are sharing the experience Dr. Gustavo Lopez, a PhD candidate at the University of Minnesota, had dealing with African Swine Fever in Russia.

Key points:

  • Infected pigs can be asymptomatic carriers of African swine fever virus (ASFv)
  • Timely detection with diagnostic testing, strict biosecurity measures and rapid removal of the source of infection are key to limit the transmission of the virus within and between sites.

In December 2014, ASFv was detected in a finishing site of a multiplier herd from a large commercial pig company located in the Russian Federation. The region had multiple reports of ASFv in backyard pigs before the outbreak. The affected company consisted of 80,000 sows in 15 farms organized as a three-site production system with each sow farm having a dedicated nursery and two finishers. The multiplier herd supplied gilts from the finisher to the gilt development unit (GDUs) for each farm. Each sow farm had a quarantine within the farm to receive the gilts from the GDU .

A 3% mortality increase was reported in one room of the finishing site. A few pens in one of the rooms had pigs affected with fever, purple ear and mild scouring. The site was being monitored for ASFv on a weekly basis before gilt shipment, following local regulations and results always came back negative.

Samples collected from the affected pigs were negative for ASFv, Classical Swine Fever, PRRSv, and Salmonella so the decision was made to resume shipment of gilts from a room with no clinical signs to the GDU.

As the days progressed, the clinical signs in the affected room worsened and affected more pens. The GDU that had just received gilts reported similar clinical signs and diagnostics on samples collected then from the multiplier finisher and the GDU confirmed the presence of ASFv at both sites.

At that time, all pig movements were stopped and a 5km quarantine area was imposed around the two affected sites. Gilts that had been sent from the GDU to five commercial sow farms, and were in quarantine tested negative to ASFv. Nevertheless as a precaution, the decision was taken to sacrifice all the gilts in the quarantines.

Protocols mandated by the government were implemented in the ASFv positive multiplier finisher and GDU which consisted of euthanasia of all pigs within a 5km radius, destruction with burial and burning of all carcasses, strict movement restrictions for vehicles and people and exhaustive disinfection protocols inside the farm and its territory.

Transportation of infected non-symptomatic animals from the multiplier finisher was the most likely route of infection to the GDU. The source of infection to the multiplier finisher is unknown, although people are thought to have played a role given the presence of ASFv in backyard farms in the area. Events such as introduction of infected pork meat, lack of proper disinfection of 3rd party trucks or non-compliance with the shower-in policy of the farm could not be ruled out. The outbreak occurred in December when temperatures were below zero Celsius and wild pig-tick-domestic pig interaction was unlikely.

It is important to point out that 12 of the 16 rooms in the multiplier finisher remained negative to ASFv until the moment of euthanasia. The sow farm and nursery multiplier were monitored for ASFv during the quarantine period and until the moment of euthanasia 6 months later. During this time, they remained negative to ASFv, even though they were within close proximity to the affected farm. Our experience indicates that a timely detection of ASFv with testing, strict biosecurity measures and removal of the source of infection as soon as possible can limit the transmission of the virus between sites.


Science Page: Effects of gestation pens versus stalls and wet versus dry feed on air contaminants in swine production (Part 1)

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 are sharing part of a scientific paper from faculty in the School of Public Health at the University of Minnesota, regarding the effect of gestation pens versus group housing and dry versus wet feed on air contaminants. This week we are sharing the first half of the results, join us next week to read the second part.


  • Pollutant levels increased as ventilation rates decreased during the cold months.
  • Pen housing lead to higher levels of NH3, respirable dust, and endotoxin when compared to stalls.


Evolving production practices in the swine industry may alter the working environment. This research project characterized the influence of stall versus pen gestation housing on air contaminant concentrations.


Eight-hour time-weighted ammonia, hydrogen sulfide, respirable dust, respirable endotoxin, and carbon dioxide concentrations and temperature were measured
regularly at stationary locations throughout a year in a facility with parallel gestation stall and open pen housing. Hazard indices were calculated using ammonia,
hydrogen sulfide, and endotoxin concentrations and relevant occupational exposure limits.

air contaminant group housing versus stall


Due to reductions in ventilation rates as outdoor temperatures decreased, season affected pollutant levels more than other factors. Concentrations were greater during the
winter than summer (Figure 1). Ammonia, dust, and endotoxin were 25%, 43%, and 67% higher, respectively, on average, in the room with gestation pens than in the room with stalls. While individual contaminant concentrations were generally below regulatory limits, hazard index calculations suggest that the effects of combined exposures on respiratory health may pose a risk to farm workers. Additionally, elevated levels of respirable endotoxin and hydrogen sulfide were detected during power washing.


Ventilation changes in response to seasonal requirements influenced air contaminant concentrations more than production practices, especially housing type.

You can also read the full article on the journal’s website.

Production Losses From an Endemic Animal Disease: PRRS in Selected Midwest US Sow Farms

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.

Perez PRRS sow farm losses Midwest

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 − 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.

For more details, read the open-access publication on the Frontiers in Veterinary Science website.


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.

Science Page: Docking the tail or not: Effect on tail damage, skin lesions and growth performance

Pig tail
Credit: Jon Olav Eikenes

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 are sharing a report by Dr. Yuzhi Li regarding the effects of tail docking in pigs.

Key points:

  • Many swine producers have been looking for an alternative to tail docking since it is a painful procedure for pigs.
  • A study examining welfare and performance of pigs with docked and undocked tails was performed
  • Performance was unaffected by tail docking, and it reduced incidence of tail damage

A study was conducted to evaluate the effect of tail docking on welfare and performance of growing-finishing pigs. Pigs, including 120 pigs that were tail-docked at birth and 120 pigs that remained with intact tails were used. Pigs were housed in 8 pens of 30 pigs in a
confinement barn for 16 weeks, with 4 pens each housing pigs of both sexes with docked or intact tails.

Results indicate that tail docking did not affect daily gain, feed intake, gain to feed ratio. During the study period, 5% of docked pigs were removed from their home pen due to tail damage, compared to 21% of intact pigs were removed for reasons associated with tail biting or tail damage. Consequently, 97% of docked pigs and 90% of intact pigs were sold for full value.

This study suggests that tail docking did not affect growth performance of pigs or eliminate occurrence of tail biting, but it reduced the incidence of
tail damage in pigs housed in a confinement system.

For more details, take a look at the full results table.

Science Page: Comparison of individual oral fluids, pooled oral fluids and Swiffer™ environmental samples of drinkers for the detection of influenza A virus and PRRS virus by PCR

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 are sharing a study done by Taylor Homann, a DVM student at the University of Minnesota in collaboration with the Swine Vet Center and Boehringer Ingelheim, regarding the comparison of several sample types to detect PRRS and flu by PCR.

Key points:

  • Pooling oral fluid samples seems to be a good strategy to determine the status of a farm (positive/negative) for influenza A virus (IAV) and PRRSV.
  • Sampling water cups using environmental Swiffer™ samples appears to be a sensitive approach to detect IAV at the pen level.
  • However, sample size has been limited to one farm.


The objective of this project was to compare the sensitivity of pooled pen oral fluids (OF) and environmental samples (Swiffer™ kits on water cups) using individual pen oral fluids as the standard.


Fifteen paired environmental and individual pen OF were collected at days 3, 7, 10, 17, 24 and 31 post placement in two different nursery farms. Environmental samples (ES) were taken using Swiffer™ cloths to sample the bottom of water cups (both pans and bowls), focusing around nipples. After individual samples were collected, pen OF were pooled by 3.


There was an overall sensitivity of 71% (IAV) and 14% (PRRS) for the ES samples compared to individual OF. Pooled oral fluids samples had an overall sensitivity of 50%(IAV)and 80%(PRRSV)relative to individual pen OF.

Homann PRRS flu Oral fluid water cup sample comparison

In summary, ES appears to be a good strategy when sampling for IAV and not a reliable option when trying to diagnose PRRSV.