Growth and estrous activity of rats fed adequate and deficient levels of phosphorus

Female Sprague-Dawley rats were fed two levels of phosphorus ad libitum and in a paired feeding arrangement to yield the following three treatments: adequate phosphorus (0.40%) ad libitum intake, low phosphorus (0.04%) ad libitum intake and adequate phosphorus pair-fed with the low phosphorus group. Feed intake, growth rate and feed conversion in rats fed 0.04% phosphorus ad libitum and in pair-fed control rats were lower (P less than 0.01) than in rats fed 0.40% phosphorus ad libitum. Seventy-five percent of the rats exhibited normal estrous cycles, as indicated by vaginal smears, throughout the 105-d period regardless of dietary phosphorus level. Breeding efficiency and number of pups per litter were not altered by dietary treatment. However, compared to either phosphorus-adequate group, dams fed 0.04% phosphorus weaned fewer (P less than 0.05) pups and pup survival to 45 d of age was lower (P less than 0.05). Average daily gain postweaning was 67% lower for pups in the phosphorus-deficient group than for those in either phosphorus-adequate group. Phosphorus deficiency in rats does not alter estrous cycles but reduces pup survivability postnatally.