Effects of salt on the growth and timing of reproduction of the deer mouse (Peromyscus maniculatus borealis)

The effects of salt on the growth and timing of reproduction in Peromyscus maniculatus borealis were investigated in the laboratory, as well as in the Kananaskis Valley, Alberta, Canada, to test the hypothesis that sodium limitation results in delayed maturation of young animals. Laboratory-born juveniles were assigned to treatment groups in which the mother received nutritionally complete food (control) or sodium-deficient food during the preweaning period. Growth of male nestlings was not affected by sodium deficiency, but among female nestlings, growth was slower in sodium-deficient groups than in controls. Juveniles were also assigned to one of two postweaning diet groups at weaning, resulting in four treatment groups based on the diet received during the pre- and post-weaning periods. For both sexes, the overall growth rate was higher in animals given nutritionally complete food in both the pre- and post-weaning period than in animals given sodium-deficient food during the postweaning period. Salt supplementation in the field resulted in the birth of significantly more litters to overwintered females than to nonsupplemented controls, but not did not result in a greater number of young weaned from each litter. Salt supplementation did not affect initiation of breeding or length of the breeding season for overwintered females, and did not affect overall growth rates or initiation of reproduction in young-of-the-year mice. Mice appear to obtain sufficient salt from their natural diets.