*Dr. Laura Bruner is with the Swine Vet Center in St. Peter, Minn.
PORCINE reproductive and respiratory syndrome (PRRS) virus continued to be the foremost topic of research projects, lectures and conversations at the American Association of Swine Veterinarians (AASV) annual meeting.
No doubt, the struggles include sow farm and growing pig losses associated with virus infections. Methods of eliminating PRRS from sow herds continue to generate discussion, primarily on how to achieve PRRS-negative piglets as quickly as possible.
The University of Minnesota recently conducted a "Time to Negative" study (Linhares et al., 2013a), enrolling 60 farms into one of two PRRS virus exposure/elimination protocols: (1) live virus inoculation (LVI) using virus harvested from the sow farm or (2) commercial PRRS modified-live vaccination (MLV).
The time needed to produce PRRS-negative pigs at weaning was, on average, shorter for herds using LVI (25 weeks) versus a commercial PRRS vaccine (32 weeks). The range of time to negative pigs weaned was 12-43 weeks, with a median of 27 weeks.
The time to regain baseline production (Linhares et al., 2013b) was defined as the number of weeks from first virus detection to the time when the number of pigs weaned per week returned to average. MLV farms tended to recover more quickly in the study and lost, on average, 1,300 pigs per 1,000 sows versus the LVI herds, which lost 2,600 pigs per 1,000 sows but produced positive pigs for longer.
An economic review of farm filtration was conducted by the University of Minnesota (Alonso et al., 2013). A modeling was done to compare 13 filtered farms with similar non-filtered cohort farms in the Midwest (average inventory of more than 2,400 head). The results of this modeling showed that filtered farms resulted in 5,927 more piglets than unfiltered farms.
In this model, the payback on the cost of filtration was five to seven years.
This model did not take into account the health and production of the downstream pig flow from filtered or unfiltered farms. When adjusting for downstream flow with wean-to-finish performance included, the modeling showed a payback of two to three years for filtered farms.
PRRS sampling and testing methods for virus detection continue to improve.
Oral fluids have provided the opportunity to sample more pigs within populations and increase the chances of finding the virus if the herd is infected. Not only is it better for detection, but samples are easier and safer to collect.
An Iowa State University study (Olsen et al., 2013) compared the probability of detecting PRRS virus infection at different prevalence rates through the use of either oral fluids or blood sampling.
Results showed that pen-based oral fluid samples provide a higher probability of detecting PRRS virus versus an individual animal sampling protocol.
At a prevalence of 12%, the probability of detecting PRRS virus was 48% using pen-based oral fluid sampling versus 12% in individual blood sampling, demonstrating that at a low prevalence, oral fluids are better at detecting the virus. At a prevalence of 36%, detection using pen-based oral fluids was 97.9% versus 36% in individual blood sampling.
Similar to PRRS virus, influenza causes much frustration for veterinarians and producers due to its high prevalence, its rapid rate of genetic change and a lack of, at this time, consistently effective control or elimination methods.
On a sow farm, off-feed events and/or fevering among gilts may be short-lived. The more challenging part is that, during these times of increased influenza activity, flu will leak from the sow farm with weaned piglets and then will continue to circulate in nurseries for many months after the original sow farm break.
Several possible strategies have been discussed, but no clear answer or solution has been identified. Regardless, swine veterinarians employ several strategies to attempt to control and eliminate flu from sow farms.
According to Yeske (2013) and Sprague (2013), strategies have included:
* Quarterly or annual mass vaccination of sow herds with a commercial or autogenous vaccine. If the specific farm virus has been isolated, it is commonly used in the autogenous vaccine, along with other common regional strains or a commercial product with strains that may offer some cross-protection. The advantage of this is that the whole herd is immunized at once, generating equal herd immunity.
* Prefarrowing vaccination. This is a common practice on sow farms. Gilts and sows will get vaccinated four to six weeks before farrowing, with the idea being to increase maternal immunity and avoid spreading the virus in farrowing.
* The use of no vaccine (Sprague, 2013). This is a practice that has been used more recently because recent research has suggested that animals with prior immunity can slow the spread of the virus throughout a population, prolonging the virus's circulation in farrowing and into the nursery.
* Gilt development vaccination with commercial and/or autogenous vaccines.
* Vaccination of nursery and grow/finish pigs. Trials of this method have been conducted with varying success. Maternal immunity from the sows can last in pigs through the mid-nursery phase, which can interfere with the efficacy of the vaccine in the growing pig.
Another complicating factor is the wide range of virus types circulating in commercial barns that makes choosing the right vaccine with the most cross-protection very difficult.
There has been increasingly more discussion centered on and around the control of preweaning mortality. Producers are beginning to experiment and/or implement a few newer protocols to increase piglet survivability from birth to weaning.
Historically, a common tool for drying piglets — towel drying piglets at birth — is becoming more widely accepted to reduce the number of pigs that are unable to regulate body temperature in the first two hours following birth, which is a critical time for determining preweaning survivability.
In addition, more farms are implementing extended or 24-hour care in farrowing to assist sows and get adequate colostrum into all piglets.
The use of these procedures has dramatically reduced the number of stillborns (2-3%) on farms and reduced preweaning mortality (4-6%) due to more focus on day 1 care, resulting in more pigs born alive and ultimately weaned.
Preweaning mortality has been a struggle at many sow farms across the U.S., but producers and veterinarians continue to find ways to improve piglet survivability preweaning.
Although not all of the answers for the elusive PRRS and influenza viruses are known, there has been a lot of exciting and practical research centered on these two diseases. Future research hopefully will continue to be strong so producers are better prepared to control or prevent these ever-changing viruses.
Alonso, C., P. Davies, D. Polson and S. Dee, 2013. Economic review of air filtration systems in North American sow herds. Proceedings of the American Association of Swine Veterinarians. p. 65.
Linhares, D., M. Torremorrell and R. Morrison. 2013a. Time to produce PRRSv-negative pigs from infected breeding sites. Proceedings of the American Association of Swine Veterinarians. p. 59-60.
Linhares, D., M. Torremorrell and R. Morrison. 2013b. Quantifying the production impact in farms going through load-close-expose programs for PRRS virus. Proceedings of the American Association of Swine Veterinarians. p. 57-58.
Olsen, C., C. Wang, J. Christopher-Hennings, et al. 2013. Probability of detecting PRRSv infection using pen-based swine oral fluid specimens as a function of within-pen prevalence. Proceedings of the American Association of Swine Veterinarians. p. 109-110.
Sprague, M. 2013. Controlling influenza in the field: Sow farm strategies that have worked for us. Proceedings of the American Association of Swine Veterinarians. p. 523-524.
Yeske, P. 2013. Controlling swine influenza in the field (sow farm strategies). Proceedings of the American Association of Swine Veterinarians. p. 521-522.