Healthy feet serve as the sturdy base on which sow productivity is built, according to experts speaking at the Feet First Sow Lameness Symposium II in Minneapolis, MN. And not all foot-related problems are readily apparent.

Surveys conducted by Iowa State University (ISU) have shown that more than 84% of sows have at least one claw lesion, and their causes vary.

Research at the University of Minnesota has shown that for every unit increase in claw lesion scores in sows’ front limbs, the number of preweaning crushing deaths increases by 8%. “If there is evidence of a problem on the sow cards, there probably is some biology behind it,” explains John Deen, DVM, professor of veterinary epidemiology at the university. “Look at the sows, not just the sow cards, to assess welfare and functionality,” he urges.

Costs of Lameness

Deen developed an economic analysis tool for Zinpro, sponsor of the Feet First Symposium, to help estimate the cost of lameness in sow herds. The tool considers the costs associated directly with the sow, such as culling, increased care costs and the cost of replacement, as well as the costs related to higher preweaning mortality and lower litter quality. He estimates lame sows can cost producers from $181 to $422 for each sow diagnosed with a foot-related problem.

Lameness is associated with decreased sow fertility. A recent German study reported lame sows had fewer than three litters prior to exiting the herd, compared to non-lame sows that averaged around 4.5 litters. Not only are the lame sows having fewer litters, but they also have smaller litters and fewer pigs born alive, according to Mark Wilson, Zinpro reproductive physiologist. Wilson says not all claw lesions lead to lameness, and some lameness problems cannot be traced to lesions. Rather, lameness may be an indicator of problems in the upper leg, such as osteochondrosis or osteoarthritis.

“The lesions of greatest concern are those that penetrate the horn wall into the corium of the foot (side view) and cause an inflammatory response, such as sidewall cracks of the outer horn wall or white line lesions,” Wilson says. Inflammation is often accompanied by pain and is one of the most apparent consequences of lameness. Many times lame sows are thin and have poor body condition. Sows with chronic lameness frequently have decreased feed intake, which tends to impact reproductive performance. Inflammation also causes changes within the body, disrupting how nutrients are utilized and even impacting ovulation, he adds.

Causes of Lameness

Lameness can be caused by nutritional problems, management, and environmental and genetic factors. Flooring type and housing (stalls vs. groups) make a difference. Rough, concrete slats can damage hooves and tear off dew claws or horn wall capsules, for example.

Deen says fighting sows may tend to suffer from more foot injuries from sliding on concrete floors when housed in pens, compared to sows housed in gestation stalls.

Some of the most common problems leading to lameness have been reported for sows with elongated claws, claw cracks, heel erosion and overgrown heels. Uneven toes can also significantly impact the incidence of lameness.

ISU research has shown that feet and leg soundness, lameness or leg problems represent the second most identifiable reason that sows leave commercial breeding herds. “Many sows are removed from the herd before they pay for themselves,” says Ken Stalder, ISU Extension swine specialist. “Under most economic and productivity situations, the parity at which a sow has been sufficiently productive for the producer to recover the initial investment is between the third and fourth parity.”

Producers report reproductive failure and feet and leg problems are the leading reasons sows are culled prior to the third parity. By comparison, sows on their sixth parity or older are mainly culled due to age and performance. Stalder says 30% or more of the sows in U.S. herds are culled before Parity 3. “If we want the sows to stay in the herd longer, we need to focus on feet and leg soundness,” he says.

Structural Soundness

Stalder tells producers it is critical to evaluate toe size when selecting replacement gilts because leg conformation starts at ground level — conforming to the shape and size of the toes.

“Ideal toes are big toes, evenly sized and spread apart. It is a simple physics lesson: if the animal has a bigger foot to spread the weight over, it is less likely to have problems,” he says. “Unequal toe size is a big problem and can be selected against. In our culling study of 3,000 sows, virtually every animal that had uneven toes had an overgrown heel or a heel lesion on the heel of the long toe.”

In those cases, more weight is distributed on the long toe. Stalder says sows with uneven toes twist their foot as they walk, which lead to abrasions and, in turn, give bacteria and infections a place to start. He recommends culling sows with toe size differences of greater than ½ in.

Additionally, Stalder says producers should consider culling gilts that are bowlegged or have toes that point in or out. Illustrations depicting common structural problems and ideal feet and leg positions are provided in a new manual, “Sow Lameness, Claw Lesions and Pathogenesis Theories” available from Zinpro Corp. (www.zinpro.com).

Replacement gilts that suffer from foot injuries, cracked hooves, heel pad abrasions, swollen joints or dew claw injuries, start with a disadvantage. “These problems are costly to treat and they take a long time to heal. Ask yourself if the gilt is worth keeping,” he suggests.

In the 3,000-sow culling study, Stalder found only 13.6% of the animals had no foot lesions, meaning more than 85% of the sows had foot lesions. “We can do better than that,” he asserts. “Culling for feet and leg soundness or lameness is likely under-reported, as a sow does not want to get up and eat, gets thin and won’t cycle, and ultimately is culled for reproductive failure,” he says.

Take a Closer Look

“There should be no question about the significance of lameness as a key factor in sow herd performance, since sow lameness has been shown repeatedly to be one of the leading factors associated with culling, euthanasia and even mortality for sows,” says Jerry Torrison, DVM, with the University of Minnesota Veterinary Diagnostic Laboratory.

Torrison outlined research projects conducted in Europe and North America that showed the widespread scope of the lameness problem. As a practicing veterinarian, he often checked sow hoof condition when they were lying in the farrowing crate.

“It appears, based on studies, that if a lesion is allowed to develop into an infection, we have associated lameness as a result,” Torrison says. Most lesions fall into three major categories, including those caused by inflammation, trauma, and mechanical damage or an inferior horn.

Research is currently looking at on-farm solutions to help prevent lameness and improve welfare-related foot problems. Some producers have sows walk through foot baths containing copper sulfate, although some experts say sows are not walked through foot baths frequently enough to make a significant difference. In addition to the foot baths, some producers apply antibacterial sprays to feet and legs. Some research has shown trace mineral mixes containing complexed zinc, manganese and copper can also help improve sow claw health while helping contribute to the welfare of the sows.

Zinpro offers guides on lesion identification and functional hoof trimming, and instructional materials pertaining to functional hoof trimming and locomotion scoring at the Web site, www.zinpro.com/feetfirst.

Lora Berg is a freelance writer from Lakeville, MN.