The Relationship between Blood Metabolites and Hormones with Intake, Gain, and Efficiency in Beef Cattle Consuming Forage then Concentrate Diets

The objective of this experiment was to determine if selected blood metabolites and hormones are related to DMI, ADG, and efficiency in cattle consuming a variety of diets. Approximately 50-d post-weaning, a group of crossbred heifers (n=76) were fed a forage-based diet containing (DM basis) 69.8% corn silage, 30% alfalfa hay, and 0.2% salt for 84 d in a Calan gate system to measure individual feed intake. BW was measured at 7 time points and a blood sample was collected on d 42 via jugular venipuncture. Following the first 84-d period, heifers were transitioned to a finishing ration containing 67.7% dry rolled corn, 20% wet distiller’s grains, 8% alfalfa hay, and 4.3% vitamin and mineral supplement. Feed intake, BW, and a blood sample were collected in the same manner as on the forage-based ration. Daily DMI, ADG, G:F, and RFI were calculated. Plasma samples were analyzed for insulin, glucagon, glucagon-like peptide-1 (GLP-1), glucose, lactate, triglycerides, cholesterol, and ß-hydroxybutyrate (BHBA). Data were analyzed using the CORR procedures in SAS. Insulin, GLP-1, and glucagon concentrations were greater on the concentrate ration compared to the forage ration (P < 0.01). On both diets, there was a negative correlation between DMI and both glucose and lactate concentrations (P < 0.05). Additionally, no correlation between GLP-1 and DMI was observed on the forage (P = 0.60) or concentrate (P = 0.27) diet. On the forage ration, there was a negative correlation between glucagon and ADG, DMI, and G:F (P < 0.05). There was also a negative correlation between triglyceride concentrations and ADG, DMI, and G:F on the forage ration (P < 0.05). On the concentrate ration, cholesterol was negatively correlated with G:F (P < 0.01) and positively correlated with DMI (P < 0.05) and RFI (P < 0.01). ß-hydroxybutyrate concentrations were found to be negatively correlated with DMI on the concentrate ration (P < 0.01). Results indicate that diet has an impact on metabolism and diet can impact how metabolism relates with production measures. It also appears there is potential to find commonalities across diets regarding metabolism and efficiency.