Ruminal and Plasma Responses in Dairy Cows to Drenching or Feeding Glycerol

Four Holstein dairy cows (137 DIM, 60 kg milk/d) were used in a Latin square with 1-wk periods to evaluate the effect of methods of oral delivery of glycerol on ruminal VFA and plasma concentrations of glucose, 6-hydroxybutyrate (BHBA), nonesterified fatty acids (NEFA), and insulin. All cows were fed only grass hay for ad libitum consumption during 12 h before the experiment. At the start of the experiment, time 0, all cows were fed 5 kg of cracked corn. Treatments administered at time 0 were: 1) control (C), no glycerol; 2) fed glycerol (F), 1 kg of glycerol solution (80% glycerol) added to the com; 3) drench glycerol (D), 1 kg of glycerol solution in 1 L of water and delivered as oral drench; and 4) tube delivery of glycerol (T), 1 kg of glycerol solution in 9 L of water and delivered into the rumen via an esophageal tube. Blood samples were collected at -1, -0.5, 0, 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 12, and 24 h after administering glycerol. Rumen samples were collected at 0, 2, 4, and 6 h. After administration of glycerol, concentrations of acetate decreased in rumens of cows while propionate and butyrate were increased by glycerol with peak concentrations at 4 h. Concentrations of glucose were increased in plasma of D and T compared with C, reaching peak concentrations at 1.5 and 3 h for D and T, respectively. Glucose response expressed as area under the curve (AUC) over baseline for 6 h was greater for D and T compared with C. Insulin concentrations in plasma were increased for D and T reaching peak concentrations at 1.4 and 1.1 h for D and T respectively. The 6-hAUCfor insulin concentrations were greater for D and T than for F and C. The BHBA was increased in plasma of D, T, and F compared with C, reaching peak concentrations at 2.5, 2.4, and 1.6h for D, T, and F, respectively. These data demonstrate that the ability of glycerol to increase plasma concentrations of glucose and insulin is dependent upon rapid delivery