In order to assess the influence of the colostral period on chloride and lactose levels and on the chloride/lactose ratio, 419 milk samples from 127 Jersey cows were analyzed. The samples were collected from healthy udders that did not present any bacterial growth in the microbiological examination. Cows were distributed into eight groups as follows: 0 ┤1/2 day; 1/2 ┤1 day; 1 ┤2 days; 2 ┤3 days; 3 ┤5 days; 5 ┤7 days; 7 ┤15 days; 15 ┤30 days of lactation. The samples were collected before milking to analyze the levels of chloride by colorimetric titration, lactose by infrared radiation, and to determine the chloride/lactose ratio. In the first 24 hours after partition, there was an abrupt reduction in chloride levels as well in chloride/ lactose ratio, associated with an increase in lactose levels. It was observed that the transition of the secretion from colostrum to milk, regarding chloride and lactose levels and chloride/lactose ratio occurred during the first week of lactation: from the 3rd day of lactation for chloride and chloride/lactose ratio and from 4th for the lactose levels. It is recommended the use the following thresholds as normal ranges for the first 24 hours of lactation: chloride <173.4mg/dL; lactose >3.94g/dL, and chloride/lactose ratio <6.11%; and between 2nd and 7th days of lactation (transition from colostrum to milk), it was suggested the use of the following values: chloride <125.9mg/dL; lactose >4.03g/dL and chloride/lactose ratio <3.54.
cow; milk; colostrum; chloride; lactose; Jersey
