Porcine respiratory disease complex (PRDC) continues to account for a majority of the economic losses associated with disease in the late finishing period. Mycoplasma pneumonia is a major contributor to that syndrome.
Just what is needed to control mycoplasma in late finishing is a source of much debate, according to James Lowe, DVM, Lowe Consulting Ltd., Albers, IL. “When you see Mycoplasma pneumonia (MHP) in late finishing, it’s merely a reflection of what’s happened in (replacement) gilts 10 months ago when they were placed on the sow farm,” he says.
Therefore, control of MHP in late finishing won’t be achieved until the MHP infection status of gilts at the time of entry into the breeding herd is managed. Four factors affect disease transmission for mycoplasma:
1. The number of pigs infected at weaning determines the disease load from MHP in growing pigs.
2. The number of pigs infected
at weaning is directly related to the number of sows shedding MHP at
farrowing.
3. Females that are infected in the 200 days prior to farrowing are likely to shed MHP to their piglets.
4. Gilts are the most likely animals to be infected in the 200 days prior to farrowing.
Route to Infection
Mycoplasma is a slow-growing bacterial organism with a long period between infection and clinical impact. That’s why infection early in life is important to provide enough time for the organism to grow into an infectious disease in pigs, says Lowe in a September presentation at the Leman Swine Conference in St. Paul, MN.
Minnesota researchers have clearly demonstrated that increasing the number of infected piglets at weaning produces disease earlier and with more severe respiratory disease associated with MHP, he says.
If more piglets infected at weaning are the cause of disease in late finishing, researchers have questioned how piglets get infected.
As so often happens, the dam is the likely source of infection affecting pigs at weaning, which means sow-to-pig transmission is the likely driver of clinical disease in MHP-infected herds, he continues.
If herds stop new introductions for at least 200 days, evidence suggests that mycoplasma shedding also stops.
To eliminate MHP, herd closure for extended periods of time will stop sow-to-piglet transmission, Lowe explains.
Guilty Gilts
Two scenarios point to new breeding animals or gilts as the most likely source of infectious mycoplasma.
First, naïve gilts could be introduced into an infected herd and become infected during the gestation period. Second, gilts could have been recently infected prior to arrival (late in the development period) and have not cleared the organism prior to arrival.
Lowe says it has been clearly demonstrated that porcine reproductive and respiratory syndrome (PRRS) does not worsen MHP transmission in pigs.
And evidence has shown that vaccines don’t alter the transmission rates of MHP. “Vaccines improve clinical signs, but just as importantly, they do not stop transmission,” he points out. “While vaccines will remain a valuable tool and serve as proven insurance from losses, they will not solve the root cause of losses or eliminate the impact of MHP on profit.”
Disease Dynamics
Critical to long-term success with mycoplasma is understanding disease dynamics within herds, Lowe states. A key step is to match infection status of replacements with current disease status of the herd.
That makes accurate diagnosis critical. Lowe’s current research collaboration with Maria Pieters, DVM, University of Minnesota, suggests:
1. There is huge week-to-week variation in the number of MHP-infected pigs, which is important for sampling.
2. Pigs shed small amounts of the bacteria, another reason sample collection is important.
3. Administration of some antibiotics appears to radically change the ability to detect mycoplasma.
4. MPH infection is a low-probability event; low prevalence rates increase the difficulty of detection.
“We need to work on continuing to develop our diagnostic agents to make the next leap forward. Our inability to precisely measure this disease at the clinical level is limiting our ability to make decisions on appropriate intervention strategies,” Lowe declares.
Early and more frequent gilt introductions may provide the right strategy for handling gilts coming into the farm, but more collaborative research is needed to confirm that, Lowe
concludes.