Vitamin D-deficient rats produce reduced quantities of a nutritionally adequate milk.

Pups raised by lactating rats deficient in vitamin D do not grow normally, and we have shown previously that this growth failure results from a maternal rather than a neonatal defect. This result indicates that vitamin D-deficient rats produce reduced amounts of milk and/or the milk they do produce is nutritionally incomplete. To examine the first of these possibilities, 3H2O and 42K in separate experiments were given to lactating rats at 13 days postpartum, and the amount of isotope transferred to their pups during the next 24 h was determined. The amount of milk produced during this period was calculated from the measured concentrations of 3H2O and 42K in milk. The specific activity of 3H2O in maternal plasma was kept constant by providing 3H2O in the drinking water of the dams. Vitamin D-deficient rats were found to produce only 19.5 +/- 1.8% determined by the 3H2O method and 23.2 +/- 1.1% by the 42K method (means +/- SD) of the amount of milk produced by vitamin D-replete rats. The composition of milk from vitamin D-deficient rats was examined to determine its nutritional value. Vitamin D-deficient milk contains elevated levels of fat, and the skim fraction contains more protein, potassium, calcium, and inorganic phosphorus but less carbohydrate than normal milk. When vitamin D-deficient dams were given two pups to nurse rather than the eight usually provided, pup growth was equivalent to that of vitamin D-replete pups. Furthermore, femur dry weights and degree of mineralization were similar in vitamin D-deficient and -replete pups of equivalent body weight.(ABSTRACT TRUNCATED AT 250 WORDS)