Technical note: Selecting the best references in gene expression experiments in liver of cows receiving glucogenic supplements during the transition period.

Measuring gene expression is a commonly used method to monitor the reaction of cells and tissues to changing nutritional or physiological conditions. Selection of appropriate reference genes is a crucial point in gene expression experiments using real-time PCR techniques. Expression of the "ideal" reference gene should not be affected by the experimental treatments or physiological state of the tissue, organ, or the whole organism. Many programs are available from which to choose the most stable reference gene. In this study, 4 algorithms--ΔCt, BestKeeper, NormFinder, and geNorm--were used to assess the expression stability of 5 candidate reference genes: β-actin (ACTB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), ribosomal protein S9 (RPS9), ribosomal protein L32 (RPL32), and TATA-box-binding protein (TBP), for use in an experiment aimed at measuring gene expression in the liver of cows fed glucogenic supplements in the transition from pregnancy to lactation. The results demonstrated that RPS9 and RPL32 were the most stably expressed in the liver under the conditions of the present experiment; the least stably expressed was ACTB.