Nitrogen plays an important role in the metabolism of living organisms due to the variety of physiological functions that involve molecules that contain it. This study aimed to estimate genetic parameters for milk nitrogen fractions and the casein:protein ratio in Mexican Brown Swiss population. Milk samples from 317 cows were used to determine total (TN), non-protein (NPN), and non-casein (NCN) nitrogen. Then, crude (CP), true (TP), and whey (WP) proteins, and casein (Cas) percentages were obtained. In addition, the ratios (%) Cas:CP (CCP) and Cas:TP (CTP) were calculated. (Co)variance components and genetic parameters were estimated using an animal model. The pedigree included 2616 animals. Heritabilities were obtained from single-trait and genetic correlations from bivariate analyses. The variation among cows was large for the studied traits. Heritability estimates could be regarded as high (> 0.7) for NCN, WP, CCP, and CTP, while for the rest of the traits, the estimates were from moderate to low magnitude. Genetic correlations estimates differed in magnitude, ranging from - 0.9 to 0.9. There is enough additive genetic variability to achieve genetic improvement for the traits studied; therefore, they could be considered in a breeding program for the studied population.
Keywords: Casein; Casein:protein ratio; Total nitrogen; Whey protein.