A Monosodium Iodoacetate Osteoarthritis Lameness Model in Growing Pigs

SIMPLE SUMMARY: Osteoarthritis is a cause of lameness in pigs. It causes pain for affected pigs and reduces profit for the farmer. From an acute problem, it progresses into a chronic condition. To study treatments for osteoarthritis, a model that mimics the functional and structural aspects of osteoarthritis is needed. To induce osteoarthritis, we injected a chemical compound (Monosodium Iodoacetate) into the carpal joint of 10 pigs (treatment group). Ten other pigs were injected with an innocuous substance (control group). We assessed their gait by visual inspection and with a device that measures weight-bearing on each limb. After 68 days, we euthanized the pigs and examined the tissues of injected joints microscopically. We could confirm structural joint changes resembling osteoarthritis in 8 of 10 pigs in the treatment group These pigs also placed less weight on their affected limb compared to the control group on day 3, 14, 28, and 56. Visually, these pigs were only more lame on day 1. Treatment with Monosodium Iodoacetate caused joint changes and lameness resembling those of naturally-occurring osteoarthritis. Although the model needs improvement for use in visual lameness, it enables the study of (drug) intervention on objective movement–pain behavior and structural joint changes. ABSTRACT: Lameness is a common problem in pigs, causing welfare issues in affected pigs and economic losses for farmers. It is often caused by osteoarthrosis (OA) in its acute or chronic form. We assessed face and construct validity of a potential model for naturally-occurring OA and its progression to chronic OA. Such a model would allow the assessment of possible interventions. Monosodium-iodoacetate (MIA) or isotonic saline was deposited in the intercarpal joint of 20 growing pigs. Functional effects were assessed using subjective (visual lameness scoring) and objective (kinetic gait analysis) techniques at several timepoints. Structural effects were assessed by histopathology at 68 days. Eight out of 10 MIA treated animals had histopathological OA lesions confirmed in the target joint, while for all saline treated animals the target joint was judged to be normal. Pressure mat analysis revealed increased asymmetric weight bearing in these animals compared to the control group on day 3, 14, 28 and 56. Visual scoring only showed a difference between groups on day 1. MIA did not cause prolonged visible lameness, thus face validity for OA under field conditions was not entirely met. Since objective gait parameters showed decreased weightbearing as a behavioral expression of pain, it may be used as a general model for movement-induced pain in pigs.