Abstract
Changes in bone metabolism throughout pregnancy and lactation in female beagle dogs were examined by histomorphometry and measurement of serum biochemical constituents related to bone. A total of eight dogs, including one dog observed repeatedly from 1 year and 8 months to 4 years and 7 months of age, were used. For double bone labeling to obtain the bone dynamic parameters, dogs were each injected twice, at an interval of 7 days, with fluorochromes such as tetracycline or calcein at the time just after mating, just after delivery, and before weaning. At the time just after weaning, the iliac bone was biopsied. Histomorphometric analysis of trabecular bone area of undecalcified iliac bone sections was performed using a semiautomatic image analyzer. Serum biochemical parameters related to bone such as parathyroid hormone, calcitonin, calcium, phosphorus and alkaline phosphatase activity were periodically measured. Bone histomorphometric analysis revealed significant increases in the mean values of osteoid volume and mineral apposition rate as compared with those of age-matched no pregnancy dogs. The mineral apposition rate measured with the passage of time was increased after delivery and was further increased before weaning compared with that at the time of mating. There were no significant changes in mean values of bone volume, mean trabecular thickness, bone formation rate and mineralizing lag time. Histological examination showed that the osteoid accumulated during the late stage of pregnancy and lactation. All histomorphometric values were significantly correlated to the age of the dam and the number of pups. Mean values of all serum biochemical parameters did not change. These results indicate that bone mineral loss occurs due to high turnover of bone metabolism during the late stage of pregnancy and lactation and is related to the age of the dam and the number of pups in dogs, in addition to the fetus mineralization and milk production.
