Two case reports demonstrate the consequences of a deficient calcium supply in dogs. The first case describes an adult dog with a history of food allergy. The dog had been fed with an unbalanced elimination diet (no minerals and vitamins supplemented) over many years and was referred with the diagnosis of osteomalacia (rubber jaw) for optimization of his ration. The second case refers to a puppy which was fed a homemade diet without supplementing the missing minerals and vitamins and suffered a femur fracture after moderate physical impact. In both cases, the computer-aided ration calculation showed a suboptimal to severely deficient supply for several minerals and vitamins, in particular calcium whereas serum calcium levels were normal. Both dogs recovered after being fed a complete and balanced diet. In conclusion, a survey of the feeding using ration calculation is essential especially in the case of potential nutrition-related skeletal disorders. Serum calcium levels cannot be used as a tool to diagnose nutritional calcium deficiency.