High-tech screening methods may help clarify why animals become lame, even identify those destined to do so.
Tucked away in a section of the College of Veterinary Medicine at Iowa State University (ISU) is the Swine Intensive Studies Laboratory. The state-of-the-art facility was a collaborative effort by specialists from the university’s animal and behavior science departments, agricultural engineering and the swine veterinary corps.
At the outset, ISU scientists were focused on providing real-time tools that pork producers and swine veterinarians could put into practical use. As is often the case, equipment and technologies from other fields — including human and companion animal medicine — were brought to the lab and adapted for swine studies. When the right equipment wasn’t available, they designed their own.
Focus on Sow Lameness
Rising quickly to the top of ISU scientists’ priority list is a challenge pork producers have grappled with for decades — sow lameness, the second most common reason sows are culled from the breeding herd, according to Extension Swine Specialist Ken Stalder. The most common cause for culling a sow is reproductive failure.
To solve the sow lameness riddle, the ISU team agreed that if they could measure how a sow distributes weight to her front and rear legs, they could begin to understand the complexities of the malady.
Joining their collective talents, Steven Hoff, agricultural engineer; Locke Karriker, swine veterinarian; Anna Johnson, swine welfare specialist; Robert Fitzgerald, a post-doctorate research assistant; Gang Sun, a graduate student; and Stalder set to work.
The fruit of their collaborative labors is the embedded microcomputer-based force plate system, which quantifies the amount of force each leg applies to a surface. With this capability, researchers are able to measure the variables associated with objective measures used to score structural soundness in the field.
The force plate is 5 ft. long, 22¼ in. wide and 4 in. tall, with ¼-in. aluminum sheets comprising the top and bottom plates. A special epoxy-sand composite coating was applied to the top plate to mimic concrete flooring, the common surface for most sow housing. This important detail helps sows avoid acting differently on an unfamiliar flooring surface.
Additionally, the force plate is designed so that the vertical forces (weight) of each leg are measured independently. The top plate is divided into four quadrants, each 30 in. long by 11 in. wide. A center bar on the force plate prevents a sow from placing more than one foot on a sensor plate.
Weight measurements are recorded from each of the four quadrants every second over a 30-minute evaluation period. A camera mounted at the front of the force plate records foot placement and movement as data is collected. Measurements are recorded for a specific time period using custom-designed data collection software.
“The force plate measurement system quantifies the amount of force each limb applies to the surface,” Stalder explains. “It measures variables that have been associated with objectively classifying structural abnormalities into degrees of lameness. Locomotion disorders can be associated with neurological disorders, lesions of the hoof or limb, mechanical structural problems, trauma, or metabolic and infectious disease.”
The ISU scientist notes that various subjective, lameness scoring systems have been developed to categorize degrees of lameness, which allows animal caretakers to quickly and affordably quantify lameness at a specific point in time. The problem is, not everyone sees — or scores — lameness the same.
“A standardized objective method for assigning lameness scores to animals — such as the force plate method — would likely be more accurate than the subjective scoring measures, and provide producers with a useful tool to assess lameness,” he says.
In a commercial application, the force plate technology could be incorporated into an electronic sow feeding system, collecting and monitoring total sow weight and leg weights on a daily basis.
Soundness in Motion
As sows leave the force plate, they move directly into a specially designed gait evaluation course configured by the ISU scientists. The first 14 ft. of the 50-ft.-long by 36-in.-wide course records an animal’s gait as it moves across the nearly 14,000 sensors underfoot.
“Sows have gait differences — almost like a fingerprint,” Karriker explains. “The GaitFour system records the sow’s gait as she moves across the mat surface.”
In addition, four high-definition cameras positioned along the course record each sow’s gait as she moves through the closed-circuit track.
In a test run of the force plate validation process, eight sows — four with visual lameness in at least one foot and four deemed normal for soundness — were analyzed. For each second in the approximate 30-minute test period, front-to-hind and left-to-right weight distributions were calculated by adding the weight placed on the respective quadrants, then divided by the total weight of the sow. This calculation provides a percentage of weight applied to each of the four quadrants, respectively.
On average, sows distributed 56.4% of their total body to their front legs, 44.6% to their rear legs. Left-to-right weight distribution differed between sows. Six sows bore more weight on their right side, two on their left.
“All sows averaged more weight on their front legs than their hind legs. But side-to-side differences had more variation. Any deviation in front-to-hind weight distribution may indicate lameness in either hind feet or both front feet,” Stalder explains.
In the early stages of testing, Stalder is optimistic that the force plate and the gait evaluation course could one day serve as an effective screening tool in commercial production systems.
“Determining the relationship between hoof lesions or leg structure, or both, and lameness would allow producers to accurately implement environmental or genetic programs to decrease lameness incidence,” Stalder summarizes. “In turn, this capability could increase sow longevity, improve individual sow welfare and improve profitability. Furthermore, the ability to objectively measure vertical forces produced by sows will potentially allow scientists and producers to identify lame individuals before clinical signs are readily apparent.”
Sow Behavior Studied
Another key component in the Swine Intensive Studies Laboratory is the behavior monitoring equipment. Johnson has viewed many hours of video footage in an attempt to understand differences in lame and normal sows’ patterns and time spent standing, lying, eating and drinking.
“Understanding the behavior of a lame sow will help us identify and treat lameness early and appropriately,” Johnson explains.
“Sows clearly eat at different rates,” she continues. “Some sows are nibblers, taking small bites, then go off to get a drink of water. Other sows are scoopers. These sows scoop up as much feed as their mouths will hold. They consume as much feed as they can in a short amount of time.”
Understanding these eating behaviors could help provide guidelines for floor-feeding sows in groups, help identify best group size, and perhaps shed some light on the best way to manage and feed lame sows, she adds.
Funding for the sow lameness and behavior work was provided by Pork Checkoff and the Iowa Pork Producers Association.