Silent Disease Leads to Lameness and Lost Production

 Damage from osteochondrosis begins as early as 1 month of age

Carlson: OC affects pigs as early as 1 month of age and the threat continues through 5 months of age, making it a critical factor in gilt development. Click to enlarge

Swine lameness has many causes, but perhaps one of the most common — yet least understood — is osteochondrosis (OC). The disease is considered the leading cause of lameness and secondary joint disease in swine, according to Cathy S. Carlson, DVM, PhD, University of Minnesota.

The condition develops as growth cartilage in the young pig begins to be replaced by bone (Figure 1). OC affects pigs as early as 1 month of age and the threat continues through 5 months of age, making it a critical factor in gilt development.

The cost of OC to swine producers is linked to slower growth, higher mortality and loss of productivity. According to John Deen, DVM, PhD, University of Minnesota, the average loss for finishing pigs associated with lameness is $23 (USD) per head, while a diagnosis of lameness in the sow herd translates into a loss of $200 to $300 (USD) per sow.

Figure 1. Normal (healthy) growth cartilage with bone development Click to enlarge

In the early 1970s, OC was recognized as an important component of lameness in commercial swine operations and confinement systems as pigs were pushed for rapid growth. Research on OC began in Scandinavia more than 40 years ago where leg weakness proved to be an economic issue. OC is also a significant problem in horses and large breed dogs.

Exploring OC development

OC is a disorder of epiphyseal (or growth) cartilage that is located at the end of long bones (articular-epiphyseal cartilage complex), as well as in the growth plate. The disease occurs in highly predictable sites, primarily the ends of the humerus, ulna and femur with lesions frequently found bilaterally.

In young pigs, the growth cartilage has an abundant blood supply. As the pig matures, the cartilage is gradually replaced by bone. However, when blood flow is restricted to growing cartilage, the cartilage dies, forming one of two types of subclinical lesions (Figure 2):

• OC latens — only visible microscopically
• OC manifesta — visible in gross examination or radiographically (x-ray)
  
  

  Figure 2. Subclinical stages of OC development Click to enlarge

  Neither OC latens nor OC manifesta results in lameness and both often heal completely as the pig grows.

  The prevalence of subclinical OC lesions in commercial swine operations is estimated to be more than 70 percent. “While subclinical lesions are quite common, a large portion of these lesions heal completely,” Carlson says. “In these cases, bone is able to form around areas of dead cartilage and complete the healing process.”

  However, if the dead cartilage collapses under the pressure of bearing weight, clinical OC develops, often resulting in lameness and pain. The clinical lesion (Figure 3) is one in which a cleft forms through the dead cartilage to the cartilage surface known as OC dissecans (OCD).

  According to Carlson, the exact cause of the failure to supply blood to cartilage that results in chondrocyte (cartilage cell) death is unknown. However, trauma due to management or environmental factors can cause a subclinical lesion to progress into a clinical lesion resulting in OCD.

  Figure 3. Clinical lesions showing joint damage due to OC dissecans (OCD) Click to enlarge

  Trauma to the bone surface causes a cleft formation within the necrotic and soft cartilage beneath the overlying normal articular cartilage at the weight-bearing surfaces. This leads to inflammation of the synovial membrane, increased joint fluid and clinical signs of lameness.

  “Once the cartilage cleft is formed, the disease proceeds down a ‘path of no return’ resulting in pain and creating a welfare issue for the animal,” Carlson says.

  “Although we’ve been studying OC for more than four decades, we don’t have a clear-cut solution to the disease,” she explains.

  One of the factors slowing research into the disease is that until very recently, the process and results of the condition could not be visualized. Advanced imaging techniques available today did not exist. Instead, animals had to be examined using histological techniques.

  “We do know that OC occurs primarily in the medial aspect and the sagittal ridge of the distal end of the humerus and the medial condyle of the femur, as well as the distal ulnar physis (growth plate),” Carlson adds (Figure 4).

  According to the Minnesota veterinarian, new research studies utilizing whole-pig scans hold promise for improved insight into OC development. The whole-pig scan technology will also allow researchers to more effectively study the effect of genetics, handling scenarios and feeding studies on managing the disease.

  Figure 4. Common locations of OC development Click to enlarge

  Prevention measures

  Although OC first emerged as pigs were being bred and fed to gain weight faster, growth rate alone is not causative for OC. Rather, it is the anatomical structure found in body conformation and joints associated with these fast-growing animals that is the stronger link to OC.

  Norwegians conducted one of the earliest studies looking at the effects of conformation on the development of OC in swine. This study followed the development of the disease over several generations and also included a scoring system for OC.

  “Through these studies, Norwegian researchers found a genetic link to OC through the boar line,” Carlson reports. “They were able to substantially decrease the prevalence of OC through careful breeding selection.”

  While research continues, several simple management steps can help prevent the formation of lesions found in the clinical form of OC. These preventive measures for pigs from 11 kg (24.2 lb) to 60 kg (132.3 lb) include:

  • Providing softer bedding

  • Decreasing or eliminating transportation events

  • Reducing steps and obstacles in the environment

  • Avoiding mixing events that lead to increased fighting

  Carlson urges swine producers to pay particular attention to the handling of replacement gilts.

  “We know that osteoarthritis can result as a secondary chronic issue in pigs that experienced OC during growth,” she adds. “Sows have an extended life cycle in the herd while carrying more weight throughout their productive life. These two factors predispose sows to osteoarthritis.”

  For more information: Contact your Zinpro Performance Minerals representative or click here.

Feet First^® Update is a publication produced by Zinpro Corporation and the Feet First Team, an international collaboration of researchers, veterinarians and nutritionists. The Feet First program focuses on swine welfare and helping improve the efficiency of pork production through the identification and prevention of lameness. Articles may be reprinted with prior permission.

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