A herd’s depop/repop program can’t stop the return of flu during fall weather.
As our outdoor thermometers drop below 90° F for the first time in three weeks, and the cooler nights close the pig barn curtains just a bit, we start to think of fall.
Although I love fall weather, I don’t love the big fluctuations in environmental temperature that take their toll on respiratory tracts of pigs. The cooler, damper weather improves viral survivability and sets up the perfect little storm that starts influenza virus rolling through the neighborhood.
Case Study
In the fall of 2009, a 2,600-sow unit broke with a respiratory disease in the finishing barns. The herd had just completed a depop/repop. The herd tested negative for porcine reproductive and respiratory syndrome (PRRS), Mycoplasmal pneumonia and Actinobacillus pleuropneumonia. High fevers (104-107° F) suggested a viral infection, possibly swine influenza virus (SIV).
To cover our diagnostic bases, and to reassure the client that we weren’t dealing with PRRS, we submitted serum samples for PRRS and mycoplasma testing and nasal swabs for SIV. We were actually relieved to get the results: SIV positive, PRRS and mycoplasma negative.
The question now was: “What do we do?” At the client’s request, we did not type the SIV for obvious political reasons. We only lost five or six pigs, less than 1% of the population on that site. Recovery seemed to be going well over a week’s period. There were 8,000 finisher spaces on the site and 4,000 nursery spaces. The nursery pigs were not clinically affected. They were located on-site about 200 yards away with prevailing winds moving from nursery to finisher.
Fortunately, biosecurity was already fairly tight. The system has a small grandparent (GP) herd that multiplies gilts for the entire system. No traffic moves back and forth other than to deliver gilts, and the trailer is disinfected before returning to the GP herd. On site, people move from nursery to finisher, but must change footwear before returning to the nursery.
Obviously, aerosol transmission was a concern on site, both from barn-to-barn, which did occur, and from finisher to nursery, which did not occur.
The SIV ran a short course through the affected barns, and we were then faced with secondary bacterial infections. We estimated nearly 80% of the finishing pigs were affected by SIV, and about 8% had secondary complications, or roughly 500 head. Therapeutic options we considered were:
1. Injectable antibiotics: With a low incidence, we felt that we might be able to give injectable antibiotics to the pigs that were having secondary infection issues.
a. Penicillin given intramuscularly to about 500 head averaging 150 lb. for three days would cost $666, plus labor.
b. Tulathromycin given intramuscularly to about 500 head averaging 150 lb. would cost $2,754, plus labor.
2. Water medication: The barns were plumbed for water medication, and we could treat 100% of the pigs with minimal labor. Two options were considered:
• Chlortetracycline to 8,000 head averaging 100 lb. for five days would cost $1,420.
• Florfenicol given to 8,000 head averaging 100 lb. for five days would cost $11,130.
Due to the low incidence of secondary problems and the concern for cost, we chose to inject affected pigs with penicillin. There was more labor cost, but less cost overall. In the end, 10 pigs averaging about 150 lb. died. The remainder recovered and went on to market.
We are certain there was a cost of disease in terms of slower rate of gain. When the barns closed out, however, there was no difference in feed efficiency and actually better daily gain than the previous turn in the same barns. We recognize, however, that seasonal temperature probably played a big part in that fall temperatures were cooler than the earlier turn during the summer. The direct cost of the disease (not including any changes to gain or efficiency) was approximately $3,400, counting mortalities and treatment costs with labor.
Looking Forward
This brings us to today. With better economic times, my client is trying to decide the value of using an SIV vaccine to prevent an outbreak this fall. The cost of vaccinating about 1,100 pigs/week would be roughly $1/pig. We realize that no vaccine is 100% effective, but if we assume that using it will protect against the strains most likely to torment his herd, it may be cheap insurance.
My client also realizes he got off very easy last time, and the next strain of flu that comes through might not be so forgiving. When it comes right down to it, I think he needs an actuary, not a veterinarian, for this one!