Effect of lipid supplementation and type of lipid on fatty acid composition of the ruminal epithelium and short–chain fatty acid transport

Abstract Text: The objective of this study was to evaluate the effect of lipid supplementation and the type of lipid on the fatty acid (FA) composition of the ruminal epithelium and short-chain fatty acid (SCFA) transport. Twenty-one Holstein steers (194 ± 10.7 kg) were blocked by BW and randomly assigned to 1 of 3 treatments differing in FA supply and composition. The control treatment (CON) contained 2.9% ether extract whereas the FA treatments contained 6.2% ether extract with the lipid coming from saturated (SAT; tallow and palmitic acid) or unsaturated sources (UNSAT; flax and Megalac). All calves were fed at 3% BW on a DM basis. After a 30-d feeding period, steers were killed and samples of the ruminal tissue were collected for FA analysis and to evaluate SCFA uptake and flux in Ussing chambers. Data were analyzed as a randomized complete block design using a mixed model with orthogonal contrasts to evaluate the effect of FA supplementation and the type of the FA supplement. There was a tendency for increased FA concentration in ruminal tissue for supplemented calves (P = 0.10), and SAT calves tended to have less FA than UNSAT (15.1 vs. 20.1 g/100 g; P  = 0.06). Ruminal tissue from SAT had a tendency for greater monounsaturated FA (37.5 vs. 32.0; P = 0.08) and had less polyunsaturated FA (17.0 vs. 23.0; P = 0.03) than UNSAT. The changes in major FA classifications were largely due to an increase for C16:0 (25.2 vs. 24.2%; P = 0.02), decrease in C16:1 (1.65 vs. 10.32%; P = 0.02), and a decrease in EPA (0.19 vs. 0.38; P < 0.01) for SAT relative to UNSAT. Acetate uptake was not affected by FA supplementation (P ≥ 0.25), but providing supplemental FA increased propionate [0.61 vs. 0.37 nmol / (cm2 × min); P = 0.05] and butyrate uptake [0.82 vs. 0.45 nmol/(cm2 × min); P = 0.03)] by the ruminal epithelium. Moreover, feeding SAT increased butyrate uptake relative to UNSAT [1.06 vs. 0.59 nmol/(cm2 × min); P = 0.01)]. There was a tendency for an increase in propionate flux across the ruminal epithelium with FA supplementation [0.65 vs. 0.56 μmol/(cm2 ×h)], but there were no differences between SAT and UNSAT. The results from this study indicate that providing supplemental FA may alter ruminal epithelial FA composition and enhance SCFA transport relative to non-supplemented calves.

Keywords: short-chain fatty acid, absorption, palmitic