Rickets is a disease of growing bones. Consequently, it usually is seen in young, weaned, growing pigs in which there is a deficiency, an imbalance, or a failure of utilization of calcium, phosphorous or vitamin D. Rickets usually is caused by a dietary deficiency of vitamin D or phosphorus. The basic abnormality is a failure of mineralization of osteoid and cartilaginous matrix, especially in growth plates. This is most obvious as a thickening and irregularity of growth plates in long bones. In confined animals not exposed to sunlight or supplemented, vitamin D may be inadequate. In pastured swine fed little or no grain or protein supplement, phosphorus may be inadequate.
Signs of rickets include poor growth, short stature, enlargement of the ends of long bones, lameness and deformation of the weight-bearing long bones. Necropsy lesions include an unusual number of recent or healing fractures, ribs that bend markedly before they fracture, and widened, thickened and irregular growth plates. Abnormal growth plates are best seen on longitudinally-sawed long bones.
Osteoporosis is a lesion of mature bones. It follows removal of much of the mineral content of the bones. It results from an imbalance between bone formation and resorption in favor of resorption. In the process there may be a softening of the bone (osteomalacia). Osteoporosis occurs often in prolific sows that mobilize minerals for high milk production. Gilts in their first lactation also are susceptible since their skeletal development may have been incomplete and there was no mineral reserve prior to pregnancy. Osteoporosis often results in fractures in the latter part of a nursing period, immediately after weaning, or during mating. Lack of exercise in confinement likely contributes to osteoporosis but inappropriate ration formulation or mixing is the most important etiological factor.
Signs of osteoporosis include lameness, recumbency, fractures and paraplegia. At necropsy, fractures often can be demonstrated in the femur, humerus or lumbar vertebrae. There may be distortions or deformities of the pelvis.
Properly balanced rations, including adequate calcium, phosphorus (in the proper ratio) and vitamin D are essential for prevention of rickets and osteoporosis. Adequate exercise also is important for normal skeletal development and maintenance. Treatment tends to be unrewarding for both rickets and osteoporosis.