ChileanJAR

This study was performed using a database of the Dairy Control Service of Bioleche Ltd., Los Angeles, Chile. The information was analyzed by a mathematical model that evaluated urea content as a dependent variable of the following factors: ordinal number of calvings, calving season, daily level of milk production, somatic cell count (RCS) and interactions between the mentioned factors. Urea content (mg 100 mL^-1) for cows of first and second or more calvings was 29.07a and 33.35b (p < 0.05), respectively. The calving season was significantly associated with mean urea values reaching 33.24a; 30.76b; 29.86b; and 30.97b (p < 0.05) in spring, summer, autumn and winter, respectively. Levels of protein less than 3.2 % and more than 3.2 % had mean values of 32.87a and 29.54b (p < 0.05), respectively. Averages were 33.47a, 31.43b, and 26.73c (p < 0.05) for daily levels of milk production between 0-15 L, between 15-25 L, and more than 25 L, respectively, and average values of 29.32a, 31.87b, and 32.43b (p < 0.05) corresponding to somatic cell count levels of less than 100,000, between 100,000 and 400,000, and more than 400,000, respectively. Significant interactions (p < 0.05) were found between the level of milk production and ordinal number of calving, and between the calving season and the level of milk production.