Changes in mRNA expression for gluconeogenic enzymes in liver of dairy cattle during the transition to lactation

The objective of this study was to profile phosphoenolpyruvate carboxybinas e (PEPCK) and pyruvate carboxylase (PC) mRNA expression in the liver of dai ry cattle during the peripartum transition and determine changes in abundan ce of these mRNA in response to protein fed during the prepartum period. Th irty-eight multiparous Holstein cows were fed diets containing either 12% c rude protein (CP) and 26% rumen undegradable protein (RUP), 16% CP and 26% RUP, 16% CP and 33% RUP, or 16% CP and 40% RUP on a dry-matter basis beginn ing 28 d before expected calving. After calving, all cows were fed a common diet through 56 d in milk (DIM). Northern analysis of RNA from liver biops y samples obtained on days -28, -14, +1, +28, and +56 relative to calving i ndicated that PC and PEPCK mRNA expression were responsive to onset of lact ation but not to prepartum protein or RUP concentration. Abundance of PEPCK mRNA was similar at -28, -14, and +1 DIM but was elevated by +28 and +56 D IM relative to precalving levels. Liver PC mRNA abundance was elevated on 1 DIM, remained elevated through 28 DIM, and declined to precalving levels by 56 DIM. The activity of PC enzyme was correlated (r(2) = 0.89) with PC m RNA abundance. The data demonstrate increased abundance of PC mRNA during t he early transition period followed by increased abundance of PEPCK mRNA du ring the postpartum period and suggest increased potential metabolism of la ctate, pyruvate, and amino acids that contribute to the liver pyruvate pool .