Combination of long-chain alcohols and fatty acids with alkanes as faecal markers to estimate feed intake and digestibility in horses and cattle fed on grass-heathland vegetation communities

Abstract

Application of long-chain alcohols (LCOH) and long-chain fatty acids (LCFA) combined with alkanes as faecal markers to estimate dry matter intake (DMI) and dry matter digestibility (DMD) of equines and cattle was assessed. Six crossbred mares, randomly divided in two groups (H1 and H2), and three nonlactating cows (C) were housed in individual stalls. Groups H1 and C were fed on a diet of ryegrass (Lolium perenne, 0.7) and heather (Erica spp., Calluna vulgaris, 0.3), and H2 received ryegrass (0.4), heather (0.3) and gorse (Ulex gallii, 0.3). Digestibility was estimated using LCOH (C28-OH and C30-OH) and LCFA (C28-FA, C30-FA, and C32-FA) as internal markers. For DMI estimation, animals received daily a paper pellet containing C24, C32, and C36n-alkanes. Intake was estimated from the faecal ratio of naturally occurring LCOH, LCFA, and dosed n-alkanes, and was compared with the known DMI values. In horses, all markers provided accurate estimates of DMD. Similarly, LCOH provided accurate estimates of DMD in cattle, whereas LCFA underestimated it (P < 0.05). Intake estimates were affected (P < 0.05) by the marker pair used in calculations. In general, the C24:C24-FA pair provided the most accurate DMI estimates. Results suggest the usefulness of combining epicuticular compounds as faecal markers to estimate DMI, DMD and diet composition of horses and cattle grazing grass-heathland communities, simultaneously.