The effect of low calcium intake and vitamin D supplements on bone structure in young growing dogs

Osteoporosis is a relatively common disorder encountered in young dogs (Campbell, 1960).Its aetiology has been the subject of a controversy over the last few decades, which has arisen from the fact that a similar disorder sometimes occurs in the human infant; this disorder has been shown to be genetically based and has been specifically called osteogenesis imperfecta (Herndon, 1956).It has been claimed by Schnelle (1940) that there is a genetic basis for osteoporosis in the young dog, although final proof has never been produced.Defects in the nutrition of the young growing dog have also been suspected as playing a part in the aetiology of the disease (Riser, 1961).Nutritional factors liable to be of importance in bone formation are the intakes of calcium and phosphorus.The absorption, utilization and excretion of Ca are affected by the amount of vitamin D available to the animal.A low Ca intake has been shown to cause bone fragility in kittens (Greaves, Scott & Scott, 1958).Vitamin D is known to improve the absorption of Ca from the gut (Harris & Innes, 193 I), but resorption of bone has also been described when vitamin D intake has been high, particularly when the diet has been low in Ca (Carlsson & Lindquist, 1955).An example of the type of daily diet that has been given in a clinical case of bone fragility in a pup is I lb minced meat, 4 pint milk, lb wholemeal bread and glucose,teaspoonful cod-liver oil, one haliborange tablet (Allen & Hanbury Ltd) and 4 teaspoonful of bone meal.The approximate contents of Ca, P and vitamin D in this diet according to McCance & Widdowson (1960) are 0.15 g Ca/Ioo g, 0.275 g P/IOO g and 1000 i.u.vitamin D on a wet weight basis.The investigation now reported has been undertaken in order to obtain further evidence on the nutritional aspects of osteoporosis in the young growing dog. E X P E R I M E N T A LAnimals.Sixteen mongrel pups of both sexes from five unrelated litters were used.They were between 6 and 10 weeks old and their nutritional history before the investigation was largely unknown.Radiography was carried out to eliminate animals with gross bone abnormalities and two complete litters were rejected on these grounds.Diets.The diet consisted mainly of meat and unfortified bread (to which no calcium 22-2