Factors influencing the self-selection of calcium in lactating rats

The effect of varying litter size and preventing milk delivery on the self-selection of calcium in lactating rats was assessed in two experiments. In Experiment 1, two groups of lactating rats, one having a litter size adjusted to four pups (n = 10) on the day after parturition and the other a litter size adjusted to 16 pups (n = 9), were given ad lib access to a 2.4% solution of calcium lactate, demineralised water, and a calcium deficient diet. Calcium, water and food intake were compared for these two groups both before impregnation and during 16 days of lactation. Females nursing 16 pups increased their calcium and food intake over the course of lactation more than did mothers nursing four pups. In Experiment 2, female rats were divided into four groups consisting of 10 nonimpregnated, 10 impregnated, 10 impregnated galactophore-cut, and nine sham-operated impregnated animals. To maintain pup health, and thus equivalent suckling stimulation among groups, litters of 8 pups were switched between galactophore-cut, impregnated and colony foster mothers every twelve hours. Over the course of lactation galactophore-cut dams showed an increase in calcium intake compared to nonlactating females and further, took in similar quantities of calcium to both intact and sham-operated impregnated animals in the first week of lactation. These studies showed that female rats do selectively increase their calcium intake during lactation. Moreover, this increase varies as a function of litter size and persists in the absence of milk delivery.