Effect of Increased Ruminal Propionate on the Expression of Gluconeogenic Genes in the Liver of Cattle on a Finishing Diet

The objective of this experiment was to determine whether increasing ruminal propionate in various amounts will lead to an increased expression of genes in the liver related to glucose metabolism. Holstein (n = 15) steers were individually fed a finishing diet ad libitum, twice a day, with free access to water. Treatments consisted of no added calcium propionate (CON), 100 g/d (LOW), or 300 g/d (HIGH). Treatments were split in half and mixed in the diet twice daily. Liver biopsies were taken on day 33 of propionate treatment and immediately frozen on dry ice. Samples were extracted for RNA, reverse transcribed to produce cDNA, and then analyzed using quantitative real-time PCR. Five genes involved in gluconeogenesis were selected as target genes, including solute carrier family 16 member 1 (SLC16A1), phosphoenolpyruvate carboxykinase 1 (PCK1), phosphoenolpyruvate carboxykinase 2 (PCK2), glucose-6-phosphatase (G6PC), and solute carrier family 2 member 2 (SLC2A2). There was a treatment effect (P = 0.04) for SLC16A1 expression, which encodes the protein MCT1, with steers on the HIGH treatment displaying the greatest expression, CON the least, and LOW was intermediate. There was also a tendency for a treatment effect on SLC2A2 (P = 0.07), which encodes the protein GLUT1, with the HIGH treatment displaying the greatest expression and CON the lowest. There was no significant treatment effect on expression of PCK1 (P = 0.27), PCK2 (P = 0.93), or G6PC (P = 0.29). These data indicate that increasing ruminal propionate may increase the expression of MCT1, which is likely due to increased propionate supply to the liver and could lead to greater glucose output from the liver.