The application of the n-alkane technique for estimating the composition of diets consumed by equines and cattle feeding on upland vegetation communities

The application of n-alkanes as faecal markers to estimate diet composition of equines and cattle was studied. Twelve mature crossbreed mares (385 ± 47 kg live weight – LW) and six adult non-lactating cows (499 ± 36 kg LW) of Asturiana de los Valles breed were divided in groups of three animals (H1, H2, H3 and H4 in equines and C1 and C2 in cattle) and housed in individual stalls. Animals received a daily total amount of 1.0 kg DM/100 kg LW of different experimental diets composed of herbaceous (Lolium perenne L.) and woody species (Ulex gallii Planchon and heather: Erica spp. and Calluna vulgaris L.). Diet composition varied among treatments: H1 and C1 – L. perenne as sole component; H2 and C2 – L. perenne (0.70) and heather (0.30); H3 – L. perenne (0.70) and U. gallii (0.30); H4 – L. perenne (0.40), heather (0.30) and U. gallii (0.30). omposition was estimated from the alkane concentrations (C27, C29, C31 and C33) in diet and faeces by least-squares procedures. Furthermore, the effect of using different sets of alkane faecal recovery, without no faecal recovery correction (R1), applying mean diet faecal recoveries (R2) or applying mean faecal recoveries across all diets (R3) was evaluated. The results showed that in equines the alkane faecal recovery was unrelated with carbon chain length. In contrast, in cattle, the alkane faecal recoveries increased with alkane chain length. The results obtained in equines suggested a negative association between diet digestibility (ranging from 0.39 to 0.58) and alkane faecal recoveries (ranging from 0.84 to 1.08) for the alkanes C27 (r2 = 0.701, P<0.001), C29 (r2 = 0.580, P<0.01), C31 (r2 = 0.604, P<0.01) and C33 (r2 = 0.742, P<0.001). Accurate diet composition estimates were obtained in equines using alkane faecal concentrations corrected or not for their incomplete faecal recovery. sults obtained in this study confirmed the usefulness of the n-alkane markers to estimate diet composition of equines and cattle grazing these type vegetation communities with very different components. However, in cattle these diet composition markers needed proper adjustment of their faecal concentrations prior to their application.