Effect of vitamin D supplementation in lactating rats on the neonatal growth.

In lactating rats consuming a commercial diet adequate in calcium, phosphorus and vitamin D, the effect of supplementation of 3000 IU and 7,500 IU of vitamin D3 on the lactational performance of the dams and soft tissue and skeletal growth in the pups has been investigated. On 28th day of age, the pups in the supplemented groups were significantly heavier than in the control group. Study of the indices of cellular growth in the liver and gastrocnemius muscle revealed that the increase in the soft tissue weight was due to a significant increase in protein, RNA and DNA contents (cellular hyperplasia) without any change in protein/DNA ratio (cell size). In the tibia, compared to controls, the dry bone weight and ash weight were more in the supplemented groups, but ash weight/dry bone weight ratio was not altered. The improvement in the neonatal growth was most probably due to the greater milk yield observed in the dams in supplemented groups and not due to any anabolic effect in the pups since direct administration of 500 IU or 1,000 IU of vitamin D3 in 10 day old pups did not increase their body weight.