Effects of metabolizable protein concentration, amino acid profile, and fiber source on the messenger RNA expression of skeletal muscle in peripartum dairy cows

摘要

After parturition, dairy cows mobilize AA from skeletalmuscle to meet metabolizable protein (MP) requirements.High mobilization may compromise cow healthand longer-term milk production. Postpartum dietswith higher MP concentrations, improved AA profiles,or MP increased at the expense of forages rather thannonforage fiber sources may attenuate muscle catabolism;however, the molecular mechanisms responsibleneed investigation. We evaluated mRNA expressionin the longissimus dorsi of cows fed postpartum dietsdiffering in MP concentration, AA profile, and fibersource. From 0 to 25 d after parturition, 40 multiparouscows received the following diets: (1) 13% deficient inMP (D-MP), (2) adequate in MP using primarily soyprotein (A-MP), (3) adequate in MP using blends ofproteins and individual AA to improve the AA profile(Blend), or (4) similar to Blend except additional proteinreplaced forage (Blend-fNDF). Biopsies were takenapproximately −5, 7, and 25 d relative to parturition.Greater dietary MP concentration (D-MP vs. A-MPand Blend) decreased expression of genes related toprotein synthesis (MTOR, RPS6KB1) and degradation(FOXO1), inflammation (IFNG, TLR4), and endoplasmicreticulum (ER) stress (HSPA5, DDIT) andincreased genes associated with lipogenesis (PPARG)and glucose oxidation (LDH, MB). In Blend versusA-MP (i.e., effect of AA profile), expression relatedto apoptosis (CASP8) and inflammation (TNFA) decreasedand genes associated with cell cycle progression(E2F1) and fast-twitch glycolytic muscle fiber type(MYH4) increased. Less forage (Blend-fNDF vs. Blend)decreased genes associated with lipogenesis (PPARG,ACACA) and ER stress (BCL2, DDIT3, EIF2AK3,PPP1R15A) and increased genes associated with inflammation(TNF), inhibition of myogenesis (MSTN),and autophagy (PEBP1). In summary and based onmRNA expression, increasing MP supply may attenuatemuscle turnover and ER stress. However, an unbalancedAA supply reduced cell cycle progression andprotein synthesis. Lower energy supplies may reducecell growth and cause autophagy.