Tue, 12 Jun 2018
Porcine reproductive and respiratory syndrome (PRRS) virus continues to plague the US pork industry. In affected breeding herds, we see a variety of problems such as a drop in the farrowing rate, an increase in abortions and post-weaning mortality or in piglets born prematurely or stillborn.
By Jose Angulo, DVM, Managing Veterinarian, PRRS specialist, Pork Technical Services, Zoetis
The respiratory consequences of PRRS tend to affect young growing pigs but can affect pigs of all ages and include slow growth and poor feed efficiency. It’s no wonder PRRS has been called the most economically significant disease affecting the US swine industry since eradication of classical swine fever. 
It’s possible to get control of PRRS, but I’ve found it requires a very organized approach based on data versus “winging it.” Vaccination plays a key role but can’t do the job alone. We have to use a set of tools and a well-planned, standardized method. I’m proposing a three-phase approach that’s been tested and proved worthwhile in the field.
Phase 1: Elimination or control?
First, determine if the goal should be PRRS elimination or control. Elimination is probably the way to go if the farm has had a PRRS outbreak less than once every 3 years. Control — the focus of this article — is probably a more realistic option for most producers and will probably make more economic sense if a PRRS outbreak has occurred more often than once every 3 years. It’s also probably a better choice if preventing a new PRRS virus infection will be difficult.
You also need to consider the impact of PRRS on herd performance, which can be determined based on key performance indicators (KPIs). For example: KPIs might be the abortion rate per 1,000 sows, the farrowing rate or the percentage of post-weaning mortality. The main objective is to produce a consistent number of quality weaned pigs.
Statistical Process Control (SPC) charts, which are graphs used to study how a process changes over time, are already used in the pork industry to track animal performance and monitor the progress of PRRS-control programs. Use them to plot past and current performance. To do this, it’s important to establish a good data-collection plan. Select a few but important KPIs and collect historical information. This will be your baseline data for comparison to the new information collected after your PRRS-control plans are initiated.
Phase 2: Collect data for discussion
Current data on the herd’s health status should be obtained. One option is a diagnostics program called STOMP® Plus (Zoetis). Through the program, samples collected by herd veterinarians are tested for PRRS virus to determine the current PRRS virus status and to check for any other diseases that may be present, then disease control strategies are devised.
We use the American Association of Swine Veterinarian’s PRRS classification criteria  to evaluate the herd’s PRRS virus status. Is the herd positive and unstable or positive and stable?
With this information in hand, the producer and herd veterinarian now have a solid foundation for analysis and can begin discussing appropriate intervention plans. We can also make intervention recommendations based on the STOMP diagnostic findings.
The ultimate goal needs to be kept in mind during this discussion phase: That goal is to achieve and maintain breeding-herd stability and minimize the reproductive and respiratory impact of PRRS. This requires managing whole-herd PRRS virus immunity with vaccination, reducing resident wild-type PRRS virus and implementing biosecurity practices to help prevent the introduction of new PRRS virus infections.
How should you measure your progress? Besides improvements in KPIs, other signs of progress would be fewer clinical outbreaks, shorter recovery phases and improved performance consistency.
Be sure to discuss obstacles that might prevent attainment of goals. For one farm, that might be improving the way replacement gilts are acclimatized, and for another, it might be solving management problems.
After it’s been decided what needs to be done to achieve effective PRRS control, figure out how the plan will be implemented and who’s going to do the work. Only then can PRRS-control interventions be implemented.
The strategy should include contingency plans addressing what to do if there are unexpected events, such as introduction of a new wild-type PRRS virus or outbreaks of other diseases such as influenza or porcine epidemic diarrhea virus.
Phase 3: Measure progress
As noted earlier, it’s a good practice to plot KPIs on SPC charts to measure the effectiveness of interventions.
Beyond that, plan to have ongoing review meetings with the farm’s staff and veterinary team to decide if the current intervention program needs to be tweaked. It’s helpful to ask simple questions such as what’s going well with the intervention plan and what’s not so modifications can be made as needed. In some cases it’s possible to change portions of the original control plan — such as a change in piglet vaccination timing, in the use of McREBEL minimal cross-fostering practices or pig flow management — as the PRRS-stability status is achieved and maintained.
Using a systematic approach as described above can greatly improve PRRS control and cut losses due to the disease. Working with a veterinary clinic, Zoetis sponsored a project to test the value of this process. The project involved 9,000 sows on four Iowa farms.  One intervention was the use of a modified-live PRRS virus vaccine administered quarterly to the entire breeding herd and administration of two doses to replacement gilts. Previously, a killed PRRS virus vaccine had been used.
There were several KPIs used to measure success. These included the abortion rate, the farrowing rate and the number of weaned pigs per sow. KPIs from August 2015 to August 2016 were compared to the previous 18 months of production using SPCs.
Breeding-herd stability was achieved in all four sow farms based on negative PRRS virus results on polymerase chain reaction testing in suckling pigs. The abortion rate per 1,000 sows was reduced and the farrowing rate increased. The number of weaned pigs per sow increased significantly along with a significant reduction of variability (p < 0.001). 
This project clearly demonstrated the value of applying a systematic approach to PRRS control in breeding herds that included monitoring and evaluation tools such as KPIs and SPC. There are many lessons learned and fewer wasted efforts when decisions are made based on data generated from the affected production system.
1. Porcine Reproductive and Respiratory Syndrome (PRRSV). Iowa State University College of Veterinary Medicine. Veterinary Diagnostic and Production Animal Medicine. https://vetmed.iastate.edu/vdpam/FSVD/swine/index-diseases/porcine-reproductive Accessed April 17, 2017.
2. Holtkamp DJ, et al. Terminology for classifying swine herds by PRRS virus status. J Swine Health Prod. 2011;19(1):44-56.
3. Angulo J, et al. Evaluation of reproductive performance after implementation of Fostera PRRS in a 9,000 sow production system using continuous quality improvement tools. Proceedings of the American Assocation of Swine Veterinarians, Denver. 2017.