Cull sow market breeding ground for disease transmission

Many sows sold into the cull sow market become “frequent travellers“ and pose a serious risk of disease transmission if a foreign animal-disease (FAD) outbreak occurs, according to a study led by Jim Lowe, DVM, University of Illinois.
calendar icon 1 May 2018
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The study was initiated after the pork industry noticed an increase in the number of cull sows showing up positive to Seneca Valley virus at processing facilities, Lowe explained to Pig Health Today.

These sows were negative when leaving source farms. Because Seneca Valley virus mimics foot-and-mouth disease (FMD), government trace-backs were conducted and eventually ruled out FMD.

Lowe designed the study to discover what happens to sows after they leave the farm and before they reach the processing plant. Are the sows exposed to Seneca Valley (or other diseases) during this time?

“We need to understand this because we slaughter 3 million cull sows in this country,” he said. “Cull sows are not a spare product and are a significant revenue source.”

14% travelled 150 miles

Researchers collected data on cull sows processed at a packing plant in Illinois during one week in May 2017.1 They obtained premise identification numbers from 2,263 sows and used them to determine farms of origin and terminal collection points of the sows.

Results showed sows originated from 297 farms in 21 states and Canada. The sows came from 16 terminal shipping locations in seven states and Ontario.

“There are a whole bunch of sows that travel a whole bunch of miles from the farm to the shipping station,” Lowe said. “Fourteen percent of the sows travelled over 150 miles from sow farm to the final point of embarkation.”

Even more astounding, 2.5% of the sows travelled five times as far from the sow farm to the shipping station as they did from the shipping station to the plant, he related.

“The cull-sow marketing system is highly valuable to us as an industry, but it results in a significant percentage of animals hanging out in the cull-sow channel for some period of time,” Lowe said.

Optimises disease transmission

The cull-sow market operates differently from the fat-hog market, which is usually direct to the packing plant. Cull sows are delivered to a collection point where the sows are sorted and sent to multiple packing plants or to other collection points.

“We’ve built a system that optimises disease transmission,” Lowe stated. “A big chunk of sows are in the marketing channel quite a while. If we look at the implications of this, we get sows that are negative at the farm and positive at the plant.

“Then those trucks roam around. Think about FMD and what else goes on cull trucks — cull cows, occasional fat cattle, and feeder steers. Think about pathogens that are multi-species, and this is a pretty good breeding ground for those.”

Study enlarged

Expect to see more research on this subject in the future. Lowe plans to conduct a much larger project with multiple plants over 10 to 12 weeks throughout a year for real quantification of the problem. The information will help the pork industry discuss with regulators how to handle cull sows in the event of a FAD incident.

“If we truly have an FAD, what does the cull-sow marketing network look like?” Lowe explained. “Where are the stop movements needed so we don’t drag disease all over the place?”

The National Pork Board, Swine Health Information Center, National Pork Producers Council and American Association of Swine Veterinarians are funding this research.


Lowe J. Understanding cull sow movements in North America: Implications on Disease Transmission. 2017 Allen D. Leman Swine Conference, September 16-19, 2017, St. Paul, Minnesota, USA. Available at Accessed February 7, 2018.

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