The objective of this study was to determine if increasing propionate alters dry matter intake (DMI), glucose clearance rate, blood metabolites, insulin concentrations and hepatic gene expression in steers fed a finishing diet. Holstein steers (n = 15; BW = 243 ± 3.6 kg) were individually fed a finishing diet ad-libitum. Steers were allocated by body weight (BW) to receive: no Ca propionate (Control), 100 g/d Ca propionate (Low), or 300 g/d Ca propionate (High) in the diet. Orts were collected and weighed daily to determine DMI. Blood samples were collected on d 0, 7, and 21, and BW recorded on d 0, 14, and 28. An intravenous glucose tolerance test (IVGTT) was conducted on d 14 and 28 of the trial. Liver biopsies were collected on d 33 for gene expression analysis. Blood samples were analyzed for whole blood glucose and lactate, plasma non-esterified fatty acids (NEFA) and insulin concentrations. Data were analyzed using a mixed model with treatment, day and their interaction included, with day and minute as a repeated measure. The control treatment had greater (P < 0.01) DMI than low and high steers. Body weight was increased in control steers on d 14 and 28 compared to the steers receiving the High treatment (P = 0.03 for the interaction). Blood glucose concentrations tended (P = 0.09) to be higher on d 21 than d 0 and 7 but was not affected by treatment (P = 0.58). Plasma NEFA concentrations were lower (P = 0.05) for control steers than other treatments, and greater (P = 0.002) on d 0 than d 7 and 21. Blood lactate concentrations were greater (P = 0.05) on d 7, than d 0 and 21, but not affected by treatment (P = 0.13). High steers had greater plasma insulin concentrations in response to the IVGTT than steers on the other treatments (P = 0.001). There was no treatment (P ≥ 0.16) or day effect (P ≥ 0.36) on glucose peak, plateau, or clearance rate. High steers had greater expression of solute carrier family 16 member 1 (SLC16A1; P = 0.05) and tended to have greater hepatic expression of solute carrier family 2 member 2 (SLC2A2; P = 0.07). These data indicate that increased propionate may decrease DMI and insulin sensitivity.

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.

The objective of this experiment was to determine if supplementing propionate alters DMI, glucose clearance rate, and blood metabolite concentrations in steers fed a finishing diet. Holstein (n = 15) steers were individually fed a finishing diet ad-libitum. Steers were allocated by BW to receive: no Ca propionate (CON), 100 g/d (LOW), or 300 g/d (HIGH) in the diet. Orts were collected and weighed daily to determine DMI. Blood samples were collected on d 0, 7, and 21, and BW recorded on d 0, 14, and 28. A glucose tolerance test was conducted on d 14 and 28 of the trial. Samples were analyzed for whole blood glucose and lactate, and plasma NEFA. Data were analyzed using a mixed model with treatment, day and their interaction included, with day as a repeated measure. The CON treatment had greater (P < 0.01) DMI than LOW and HIGH. BW was greater for CON throughout the experiment and all treatments had an increased BW on day 28 (P = 0.03 for the interaction). Whole blood glucose concentrations tended (P = 0.09) to be higher on d 21 than d 0 and 7, but was not affected by treatment (P = 0.58). Plasma NEFA concentrations were lower (P = 0.05) for CON than other treatments, and greater (P = 0.002) on d 0 than d 7 and 21. Whole blood lactate concentrations were greater (P = 0.05) on d 7, than d 0 and 21, but was not effected by treatment (P = 0.13). There was no treatment (P ≥ 0.16) or day effect (P ≥ 0.36) on glucose peak, plateau, or clearance rate. These data indicate that supplemental propionate may decrease dry matter intake but might not alter glucose clearance rate.