Effects of Abomasal Infusion of Linseed Oil on Responses to Glucose and Insulin in Holstein Cows

Schematic representation of experiments. Abomasal infusion of treatments were performed every 8h during the first 3 d of each period, at 0700, 1500, and 2300h, and every 4h on d 4 and 5 (at 0700, 1100, 1500, 1900, 2300, and 0300h). Cows were fed at a rate to meet individual maintenance requirements (NRC, 2001) in experiment 1. Feeding was suspended at 0700h on d 3 of experiment 2 to promote mobilization of body reserves. Blood samples were collected daily before 0700h infusions and feeding. Intravenous glucose tolerance tests were performed at 0900h and i.v. insulin challenges at 2100h on d 5.

Experiment 1 (fed state): A) Effect of abomasal infusion of linseed oil or tallow (0.54g/d per kg of BW) on plasma glucose concentration after i.v. glucose tolerance test (IVGTT; 0.25g/kg of BW of glucose i.v.). Cows were fed at a rate to meet maintenance requirements and treatments were administered for 122h before IVGTT. Fixed effects in the statistical model: sequence (P=0.13), treatment (P=0.45), time (P<0.001), and treatment×time (P=0.94). B) Effect of treatments on serum insulin concentration after IVGTT. Fixed effects in the statistical model: sequence (P=0.92), treatment (P=0.14), time (P<0.001), treatment×time (P=0.24), and BCS covariate (P=0.09). P-values reflect statistical analysis with log-transformed data.

Experiment 2 (feed restriction): A) Effect of abomasal infusion of water, linseed oil, or tallow (0.54g/d per kg of BW) on plasma glucose concentration after i.v. glucose tolerance test (IVGTT; 0.25g/kg of BW of glucose i.v.). Treatments were administered for 122h and cows were feed restricted for 50h before IVGTT. Fixed effects in the statistical model: treatment (P=0.40), time (P<0.001), and treatment×time (P=0.95). Contrasts: water vs. fat infusion (P=0.53); linseed oil vs. tallow (P=0.24). B) Effect of treatments on serum insulin concentration after IVGTT. Fixed effects in the statistical model: treatment (P=0.51), time (P<0.001), and treatment×time (P=0.97). Contrasts: water vs. fat infusion (P=0.50); linseed oil vs. tallow (P=0.65). P-values reflect statistical analysis with log-transformed data.

Experiment 2 (feed restriction): A) Effect of abomasal infusion of water, linseed oil or tallow (0.54g/d per kg of BW) on plasma NEFA concentration after i.v. glucose tolerance test (IVGTT; 0.25g/kg of BW of glucose i.v.). Treatments were administered for 122h and cows were feed restricted for 50h before IVGTT. Fixed effects in the statistical model: treatment (P=0.48), time (P<0.001), and treatment×time (P=0.92). Contrasts: water vs. fat infusion (P=0.85); linseed oil vs. tallow (P=0.23). P-values reflect statistical analysis with log-transformed data. B) Effect of treatments on plasma NEFA concentration change (delta NEFA) after IVGTT. Fixed effects in the statistical model: treatment (P=0.34), time (P<0.001), and treatment×time (P=0.73). Contrasts: water vs. fat infusion (P=0.64); linseed oil vs. tallow (P=0.17).

Experiment 2 (feed restriction): A) Effect of abomasal infusion of water, linseed oil or tallow (0.54g/d per kg of BW) on plasma NEFA concentration after insulin challenge (IC; 0.1 IU/kg of BW of insulin i.v.). Treatments were administered for 134h and cows were feed restricted for 62h before IC. Fixed effects in the statistical model: treatment (P=0.67), time (P<0.001), and treatment×time (P=0.91). Contrasts: water vs. fat infusion (P=0.52); linseed oil vs. tallow (P=0.54). P-values reflect statistical analysis with log-transformed data. B) Effect of treatments on plasma NEFA concentration change (delta NEFA) after IC. Fixed effects in the statistical model: treatment (P=0.72), time (P<0.001), and treatment×time (P=0.90). Contrasts: water vs. fat infusion (P=0.88); linseed oil vs. tallow (P=0.43).