Mycoplasma hyopneumoniae: Elimination or control?
By Clayton Johnson, DVM
Carthage Veterinary Service
Integrated Veterinary Network
For decades, we’ve lived with Mycoplasma hyopneumoniae (M. hyo) and have come to accept it as an endemic pathogen of swine. Heck, we even named it “enzootic pneumonia,” which implies this respiratory pathogen will forever hinder pig growth and producer profitability.
Now is not the time to surrender and accept M. hyo as a fact of swine production. In fact, as respiratory challenges from other viruses continue to mount, the economic impact of M. hyo becomes even greater. This mounting threat also comes at a time pork producers are telling us they need to reduce the use of antibiotics, which are valuable tools for control.
Given both of these current realities, eliminating M. hyo is proving to be more cost effective than controlling M. hyo for an increasing number of herds. In my estimation, the potential value for eliminating this pathogen has never been greater.
What’s the best approach for your farm?
The financial models for deciding on M. hyo elimination or control are relatively straightforward. First, we need to define the cost of elimination and how that compares to the actual impact of elimination. We also need to consider the future exposure rate of M. hyo and its future impact. Furthermore, we have to figure out how much M. hyo elimination will save us before the herd is exposed to M. hyo and then compare that to the cost of an M. hyo outbreak in a naive herd.
Ultimately, the best approach for a farm is based on the total cost savings for eliminating M. hyo compared to the frequency and cost of future M. hyo outbreaks.
‘Load, close and homogenize’
When I review M. hyo elimination versus control options with producers, the first thing we lay out is the elimination plan itself.
Typically, M. hyo-elimination plans are built around a “load, close and homogenize” program. We bring in as many gilts as the farm can handle, close the herd to new gilts and wean all piglets off site.
Next, we mix pigs with M. hyo clinical signs throughout the facility to ensure M. hyo exposure of all animals on the farm. That homogenizes, standardizes and eventually stabilizes herd immunity. The details and cost of this program vary and are specific to each farm.
Breeding costs — more specifically missed breedings — need to be considered in the analysis because they can be a huge part of the M. hyo-elimination cost. Producers with no on-site gilt-development program will have no supply of gilts throughout the herd closure period and can’t reach their weekly breeding target. Farms with on-site gilt development will have a built-in supply of gilts while their herd is closed.
Another way producers can maintain their monthly breed target is by initiating an off-site breeding project in which an off-site farm is used to house M. hyo-naive gilts of breeding age. These gilts are bred during the end of herd closure and moved to the farm prior to farrowing but following the elimination of M. hyo.
Review impact of elimination
Next, we review the potential impact of M. hyo elimination. Here we need to work with producers to determine what they think M. hyo infection is costing them. The impact of M. hyo is generally greatest in growing pigs. However, we also need to factor in the impact of respiratory co-infections, as well as management practices — e.g., post-weaning commingling with other sources and all-in/all-out (AIAO) versus continuous-flow strategies.
It’s important to understand that post-weaning flows challenged with some combination of porcine reproductive and respiratory syndrome (PRRS) virus and/or influenza A virus will actually benefit more from M. hyo elimination than flows where M. hyo is the primary respiratory challenge. In fact, there’s a large magnitude of difference between these two scenarios.
For example, the impact on performance from M. hyo elimination will be lower in herds that commingle with other M. hyo-positive sources than it will be for herds that do not commingle or commingle with M. hyo-naive sources. Likewise, post-weaning flows that create AIAO batches of pigs will benefit more from M. hyo elimination than flows that move through continuous-flow facilities.
Medication strategies currently employed for M. hyo control post-weaning should also be reviewed. Are we comfortable removing this cost while trying to eliminate M. hyo? Will there be additional value by demonstrating a reduction in antibiotic use and, if so, what’s the value?
Consider future M. hyo outbreaks
The most difficult assumptions involve the impact of future M. hyo outbreaks. Virtually all producers I have this conversation with already have M. hyo-positive herds, so we rarely have an accurate estimate of historical M. hyo-exposure events.
To create these assumptions, I often rely on pig density in the area, the M. hyo status of neighboring farms and the farm’s biosecurity capabilities — including pig-house filtration status — to come up with our best “SWAG” — our best, scientific, wild-ass guess — of how often the farm will have an outbreak.
If pig houses on the farm are not filtered, they’re in a pig-dense area and the majority of neighboring farms are M. hyo positive, I have to assume M. hyo exposure will be frequent. If the farm is not in a pig-dense area, is surrounded by only M. hyo-naive neighbors and/or are filtered and the farm has excellent biosecurity capabilities and behaviors, it’s reasonable to assume M. hyo exposure will be infrequent.
PRRS-exposure history can be used as a proxy for M. hyo-exposure projections, but use caution with this estimate considering the significant differences in pathogen stability in various environmental conditions.
Figure out best- and worst-case scenarios
Admittedly, any economic analysis contains flawed assumptions. Where assumptions aren’t clear cut, we can use a range and figure out the best- and worst-case scenarios. Both ends of the impact range are plugged into our model to see if it changes the decision based on either end of the assumption range.
If we have the same outcome using either end of the assumption range, we don’t get too hung up on which assumption to use. We “ballpark” it in the middle, knowing it doesn’t affect the model significantly enough to warrant further refinement. If it does appear to be critical to the decision — one end of the assumption range recommends control versus eradication and the other end recommends the opposite — we dig into the analysis further to reach a more precise assumption.
Using all of the cost and impact assumptions outlined above, we can create a financial analysis that forecasts the performance and economic outcomes for M. hyo control versus M. hyo elimination. This approach helps me as a veterinarian provide an informed recommendation to producers about the best way to manage M. hyo in each individual herd.