Altering systemic acid-base balance through nutrition failed to change secondary sex ratio

There is evidence that differences in either maternal blood pH or dietary mineral content can result in alterations in secondary sex ratio in mammals. Altering the proportions of certain dietary minerals is known to influence blood pH, offering a possible explanation for this effect of diet on secondary sex ratio. The present study was performed to investigate whether altering blood pH by manipulating the dietary cation-anion difference (DCAD) would alter secondary sex ratio. The DCAD is calculated (in mEq per 100 g dry matter) as the difference between metabolically strong cations (Na + K) and metabolically strong anions (Cl + S) in the diet. Three hundred female mice were randomly allocated to either a low or high DCAD ration for 3 weeks before coitus. Urine pH was monitored before beginning the experiment, as well as before and after the breeding period, as a proxy for blood pH. Mice on the low DCAD diet had a lower urine pH (mean (± s.d.) 6.0 ± 0.1) than mice on the high DCAD diet (8.2 ± 0.6), but DCAD did not affect the percentage of mice that became pregnant, the number of offspring per pregnant mouse or the sex ratio of the neonate group. These results suggest that blood pH alone does not alter sex ratio and that an altered systemic pH is not the reason for reported mineral-related variations in sex ratio. © CSIRO 2007.