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

Abstract

The objective was to study the effects of abomasal infusion of linseed oil, a source rich in n-3 C18:3, on whole-body response to insulin (experiment 1) and on insulin antilipolytic effects during feed restriction (experiment 2). In experiment 1, eight nonlactating, non-gestating cows were assigned to a crossover design, fed to meet maintenance requirements, and infused abomasally with either linseed oil (LIN) or tallow (TAL) at a rate of 0.54g/kg of body weight per d for 5.5 d. Infusions were performed every 8h during the first 3 d of each period and every 4h thereafter. Intravenous glucose tolerance tests (IVGTT) were performed on d 5 of each period, followed by i.v. insulin challenges (IC) 12h later. In experiment 2, six nonlactating, nongestating cows were assigned to a replicated 3×3 Latin square design. The experimental protocol included a water (WTR) treatment and feeding was suspended on d 3, leading to 50 and 62h of feed restriction before IVGTT and IC, respectively. Clearance of glucose during IVGTT and IC was not affected by treatments in either experiment. However, LIN had an insulin sensitizing effect in experiment 1, because a lower insulin concentration led to the same clearance of glucose as TAL. In experiment 1, plasma nonesterified fatty acid (NEFA) concentration was low, reflecting a postprandial state, but NEFA was greater for LIN than TAL during IVGTT (108 vs. 88±4μEq/L) and IC (133 vs. 83±9μEq/L). In experiment 2, insulin concentrations during IVGTT did not differ across treatments. Basal plasma NEFA concentration before IVGTT tended to be greater for LIN than for TAL (612 vs. 508μEq/L). Plasma NEFA clearance rate during IVGTT was greater for LIN than for TAL (2.8 vs. 2.5%/min), leading to a shorter time to reach half NEFA concentration (25 vs. 29min) and greater absolute value of NEFA response area under the curve [AUC; −64,150 vs. −46,402 (μEq/L)×180 min]. Data suggest that LIN enhanced the antilipolytic effects of insulin. Yet, other factors could have been involved because plasma NEFA concentration before IVGTT was 104μEq/L greater for LIN than TAL for unknown reasons.