In the last decade, an intensification process has been developed in the dairy production of northwestern Argentina. In Salta province, the bovine milk basin is located in Lerma Valley. Minerals are essential for dairy cows, and the amounts normally found in most feeds are inadequate for high milk production. If these requirements are scarce or not met, deficiency symptoms can occur. As in other parts of the world, mineral imbalances are one of the most important problem in Salta’s basin. To known imbalances prevalence of calcium (Ca), phosphorus (P) and magnesium (Mg), 584 dairy cows of 4 farms of basin Lerma Valley were sampled in 4 opportunities. At each visit were bled from the jugular vein of 9/10 animals in each category: prepartum, fresh cow, 2nd and 3rd third of lactation. Values Ca and Mg serum were obtained by atomic absorption spectrophotometry and P values by UV-visible spectrophotometry. Associations between variables were analyzed using linear correlation and linear regression, in addition to analyzing the probability of occurrence of hypocalcemia by odds ratio. Differences between variables and moment of lactation were examined by ANOVA and Tukey’s test and Chi-squared using Fisher’s test. The mean serum Ca was 8.85 mg/dL, with no differences found all over the periods. The average prevalence of hypocalcemia was 46.2% in all production periods. The mean serum Mg was 2.26%, with a prevalence of 10.6% hypomagnesemia. Animals with hypomagnesemia had a 3.5 times greater chance of having hypocalcemia compared with those with normal values. The prevalence of animals with abnormal values of P was high (48.3%), without association with hypocalcemia levels. Based on our results, there are potential risks of imbalances Ca, Mg and P in the dairy herds of the Lerma Valley.