The influence of viruses on sow herds has always been a challenge. Viruses that have caused major disease problems on sow farms in the past 5-10 years include swine influenza virus (SIV), porcine reproductive and respiratory syndrome (PRRS) and pseudorabies (PRV). These viruses cause similar disease signs and must be weighed as we discuss the impact of viral diseases in pork production units.
Some common signs include off-feed sows with elevated temperatures, increase in depression and lethargy, increase in coughing and other respiratory problems. All viruses that cause higher fevers may result in abortions. PRRS virus and PRV can cause abortions due to the impact of the virus on the unborn piglet. The effects of these viruses on piglets in the farrowing barn include a low-grade cough, off- feed piglets and gaunt, feverish piglets with an increase in depression.
PRV can also cause central nervous signs or paddling symptoms in piglets. These nervous signs are not common with either SIV or PRRS.
A typical SIV outbreak occurs in finishing pigs or sow herd and moves rapidly through the rest of the pigs on the farm. There is a high incidence of barking cough due to the effect of the influenza virus by irritating the bronchioles of the lungs. SIV is typically highly infectious, meaning the majority of the pigs are clinically affected, but low death loss.
In the past, there has primarily been one strain of SIV called H1N1. Recently, however, various diagnostic labs have identified a new strain referred to as H3N2. This different strain has resulted in significant number of respiratory outbreaks in sow herds and finishers. The traditional vaccines have not been effective for this new strain of SIV. Signs have also varied with this new strain, coughing and an increase in abortions.
The PRRS virus has created lots of problems in the last five years. This virus has been linked to abortion syndromes and off-feed sows. In addition, it causes a severe respiratory problem in nurseries and finishers. There appears to be large strain variations within the PRRS virus. These strain variations dictate how pathogenic a specific PRRS strain is.
Primary control methods for PRRS revolve around the isolation and acclimation (I/A) policies on specific farms and the status of the source herds. It is important to have replacement stock brought to the farm early enough to allow a minimum of 60 days I/A. Some producers have brought in feeder gilts or weaner pigs as replacements, which gives a longer time for acclimation.
PRV causes off-feed sows, a chronic cough, increased fever and depression. In vaccinated herds for PRV, there is usually no disease signs identified.
Case Study No. 1 I was called to a 1,500-sow, farrow-to-wean facility. This unit had been in operation for two years. Start up was excellent with farrowing rates over 85% and average wean weights over 11 lb. at 14-16 days.
In early December, a number of sows were off feed and feverish. Within the next 3-5 days, 60-70% of the herd had similar symptoms. About 50 sows aborted and replacement gilts seemed to be the hardest hit with respiratory distress, lethargy and off feed. Piglets in the farrowing barn exhibited a cough and were rough-haired and poor doing. Pigs were born weak and an increase in diarrhea was noted. Preweaning death loss went from under 8% to excess of 20%. The number of stillborns and mummies increased over the next month and the incidence of poor-doing pigs increased significantly.
Tissues were collected from sows and gilts that died and sent to a diagnostic laboratory. In addition, serum samples were retrieved to do serology.
These sows were PRRS positive with titers ranging from 1-2 on ELISA. SIV titers were also fairly high and the diagnostic lab reported sows positive for SIV. Piglets in the farrowing barn had interstitial pneumonia indicating PRRS virus. Pigs in downstream nurseries and finishers were positive for PRRS. The sows had been vaccinated for SIV as replacement gilts, but received no booster shots.
For control, the entire herd was vaccinated with SIV vaccine and a killed, autogenous PRRS vaccine. Some sows were given antibiotic injections to help control secondary bacterial problems. Over the next 6-8 weeks, production continued to improve with sows coming back on feed and piglet quality reverting to previous levels.
Case Study No. 2 I was called to a 350-sow farm that had a sudden onset of off-feed sows and an acute barking cough. Temperatures of the sows ranged from 104.5 to 106 F. There had been no abortions and most sows recovered within 3-4 days. Penicillin injections were given to sows with respiratory distress. One sow was euthanized and sent to a diagnostic lab. SIV was isolated from this sow. By the time the farm received the positive SIV diagnosis, sows were back on feed without disease problems. PRRS titers were fairly high but no disease or diagnostic evidence was found.
The viruses of SIV, PRRS and PRV can create big problems. Producers and their veterinarians should attempt to make a definitive diagnosis of which viruses may be present. Once a diagnosis is made, producers can mull various control measures. Contact your local veterinarian to assist you if you have any of the described disease problems.