Research has shown that milk yield (MWT) accounts for only a moderate amount of variation in pre-weaning average daily gain (PRWADG). This study was proved that milk fatty acid methyl esters (FAME), alone and in combination with MWT, could improve accuracy of prediction of PRWADG using stepwise regression and partial least squares (PLS) models. The milk fatty acid composition of beef cows is markedly influenced by nutritional factors and also significantly controlled by a few major genes effects. In the second part of this study, three genes, diacylglycerol O-acyltransferase 1 (DGAT1), stearoyl-CoA desaturase 1 (SCD1), and fatty acid synthase (FASN), were selected to determine their associations with milk fatty acids of beef cows sired by 6 different breeds (Bonsmara, Brangus, Charolais, Gelbvieh, Hereford and Romosinuano) out of Brangus dams. Results showed genotypic differences in variants of the DGAT1 gene for saturated fatty acid (SFA), the ratio of omega-6 to omega-3 fatty acids (N6/N3), C14:0, C18:1n9c. C22:1n9 and C22:5n3 (P < 0.05), and for omega-3 fatty acids (N3) and the ratio of polyunsaturated fatty acid to saturated fatty acid (PUFA/SFA) (P < 0.10). The variation in the SCD1 gene also influenced vaccenic acid, C20:0 and C21:0 (P<0.10). For FASN gene, genotypic differences affected the composition of C22:1n9 (P<0.05) and C22:0 (P<0.10). However, genotypic differences for each fatty acid category were not consistent among the different sire breeds.Animal Scienc
