Lactation induces upregulation of the ubiquitin-mediated proteolytic pathway in skeletal muscle of dairy cows but does not alter hepatic expression

The current study investigates regulation of mRNA expression of components of ubiquitin-mediated proteolysis in transition dairy cows. Longissimus dorsi muscle (exp. 1) and liver (exp. 2) biopsies were collected from Holstein dairy cows at 27 and 16 d pre-partum, respectively, and 3 and 10 d post-partum, respectively. Regulation of C8, E2, and ubiquitin mRNA expression was determined. Upregulation of skeletal muscle C8 (P = 0.09) and ubiquitin (P = 0.004) mRNA expression occurred post-partum compared with pre-partum. No regulation of hepatic mRNA expression was observed. In conclusion, ubiquitin-mediated proteolysis may contribute to skeletal muscle protein degradation during the periparturient period, and could provide a potential mechanism for attenuation of body protein loss at the onset of lactation.Key words: Lactation, ubiquitin-mediated proteolytic pathway, muscle (skeletal), liver