Enzyme activities and milk performance by clusters of growth hormone gene (GH) and beta-casein (beta-cN) in German Holsteins

The examined enzyme activities show the same trend as milk yield. The enzym e activities for combined aminopeptidases increased nonlinearly to a higher milk performance. Lower physiological load contributes to better fertility . The increasing enzyme activity of lysosomal esterase is connected with a higher ATP need, the protein synthesis increases simultaneously. The geneti c effects of milk protein genotypes beta -casein(A2A2) are superior to thos e of beta -casein(A1A1). The effect of days open shows the same trend in mi lk production and fertility. A high milk performance could be combined with high fertility on a genetic basis.