Fatty acids in forages. II. In vitro ruminal biohydrogenation of linolenic and linoleic acids from timothy

Abstract

Polyunsaturated fatty acids from forages are hydrogenated in the rumen and this biohydrogenation depends on several factors. The objective of this study was to determine and compare in vitro ruminal biohydrogenation of linolenic (C18:3) and linoleic (C18:2) acids in timothy harvested from different growth stages, produced with or without fertilization, or conserved by different methods. In exp. 1, timothy was grown with (120 kg ha-1) and without N and harvested at four growth stages. In exp. 2, harvested timothy was conserved as fresh grass, wilted grass, dry hay, haylage, and silage, some with additives: haylage with lactic acid bateria (LAB), haylage with formic acid, silage with LAB, and silage with formic acid. Samples were incubated with rumen fluid in three trials to compare: (1) samples from exp. 1; (2) the five basic conserving methods of exp. 2, and; (3) how the silage additives affected biohydrogenation of C18:3 and C18:2. Effective disappearances and ruminal bypass of C18:3 and C18:2 were fastest in timothy harvested at stem elongation but slowed linearly with increasing maturity (P < 0.01). Although N fertilization increased (P < 0.01) the effective disappearance and bypass of C18:3 and the bypass of C18:2, it did not affect their rate of disappearance. These last rates were not affected by maturity, but were faster in haylage and silage than in hay (P < 0.01). Ruminal bypass of C18:3 was greater in fresh grass, wilted grass, and dry hay than in haylage and silage (P < 0.01). Additions of formic acid and LAB to haylage and silage had no significant effect on C18:3 and C18:2 disappearances and bypass. To maximize the amount of C18:3 that bypasses ruminal biohydrogenation timothy should be fertilized with N, harvested at an early growth stage, and conserved as dry hay. Key words: Biohydrogenation, fatty acids, N fertilization, maturity, conservation methods, timothy