Clinical signs and bone changes associated with phosphorus deficiency in beef cattle.

For 10 years, 42 female Herefords (as they progressed from weanling calves to aged cows) were fed diets individually, with phosphorus (P) content being the only variable. During growth and the first 3 gestations, clinically evident differences were not associated with 2 dietary treatments (approx 12 and 38 g of P/day). During the next 2 gestations (2 years), half the cows from each original treatment group were fed less than 6 g of P (n = 21 cows, 11 from the group fed 12 g of P/day and 10 from the group fed 38 g of P/day) daily. The other half were fed diets supplying approximately 8 g of P (n = 11 cows fed 12 g of P/day) and 35 g of P (n = 10 cows fed 38 g of P/day) daily. During the last 3 years of the experiment, all remaining cows were fed diets containing 12 g (n = 19 cows originally fed 12 g) or 19 g (n = 17 cows originally fed 38 g) of P/day. Cows fed diets containing less than 6 g of P/day developed an insidious and subtle complex syndrome characterized by weight loss, rough hair coat, abnormal stance, and lameness. Spontaneous fractures occurred in the vertebrae, pelvis, and ribs. In severely affected cows, fractures did not heal properly. Some bones were demineralized markedly, and the cortical surfaces were porous, chalky white, soft, and fragile. Osteoid tissue was not properly mineralized. Radiography revealed diminished bone density (osteoporosis), cortical thinning, and resorption of trabeculae. Time-related availability of dietary P initiated excessive turnover of bone, with resultant structural changes and impaired function.(ABSTRACT TRUNCATED AT 250 WORDS)