In order to assess the influence of the colostrum period on pH and, electrical conductivity, we collected 418 milk samples from 127 Jersey cows. The samples were collected from healthy udders that did not present any bacterial growth in the microbiological examination. They were divided into eight groups as follows < 1/2 day; 1/2 and 1º day; 2º day; 3º day; 4º and 5º day; 6º and 7º day; 8º to 15º day; 16º to 30º days of lactation. The samples were collected before milking and the following analyses were conducted: pH, electrical conductivity. In the first 24 hours of lactation, there was an reduction in electrical conductivity value, associated with an increase in pH value. We observed that transition of secretion from colostrums to milk, occurs during the first week of lactation; from 6 rd day of lactation for pH value and 3th day for electrical conductivity value. We recommend the use the following figures as normal ranges for the first 24 hours of lactation (colostrum period): pH ? 6,51 and electrical conductivity ? 6,33 mS/cm; while for the interval between 2nd and 7 th days of lactation (transition from colostrum to milk) we suggest the use of the values as normal ranges: pH ? 6,66 and electrical conductivity ? 5,93 mS/cm.