Inter-individual variation in adaptive capacity at onset of lactation: Linking metabolic phenotype with mitochondrial DNA haplotype in Holstein dairy cows.

Modern-day dairy cows express great variation in metabolic capacity to adapt to the onset of lactation. Although breeding programs increased the breeding value for longevity and robustness in the sires, a respective phenotype in female offspring has not been improving as predicted. Fundamental energy generating pathways such as mitochondrial fatty acid oxidation might have a crucial role for robustness and metabolic efficiency in dairy cows. Therefore, mitochondrial enzyme expression was examined in liver samples of one set of animals before and after calving. Furthermore, the mitochondrial DNA sequence was determined for each individual of a second set of animals using liver samples. Results from the first trial indicate that the expression and extent of phosphorylation of acetyl-CoA carboxylase (ACC) is the major key step for modulating fatty acid flux into the mitochondria at early onset of lactation in Holstein dairy cows. In the second trial, mitochondrial DNA sequencing and identification of mutation patterns yielded three major haplotypes. Haplotype H2 was closely associated with liver fat content, plasma glycerol and acyl-carnitine concentrations. The mitochondrial DNA haplotype, which is a feature of the maternal lines, might be related to the inter-individual variation in metabolic capacity of Holstein dairy cows.