Comparison of long-chain fatty acids and alkanes as markers to estimate diet composition of equines and cattle consuming heathland vegetation species L.M.M. Ferreira a, ⁎, R. Celaya b , A.S. Santos a , V. Falco c , C. Guedes a , M.A.M. Rodrigues a , K. Osoro b a CECAV- Departamento de Zootecnia, Universidade de Trás-os-Montes e Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal b SERIDA- Servicio Regional de Investigación y Desarrollo Agroalimentario, PO Box 13, 33300 Villaviciosa, Asturias, Spain c CQ-VR, Centro de Química – Vila Real, Departmento de Agronomia, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal article info abstract Article history: Received 12 February 2010 Received in revised form 7 April 2010 Accepted 9 April 2010 This study aimed to evaluate the application of long-chain fatty acids (LCFA) as an alternative or as a complement to alkanes to estimate diet composition in equines and cattle. Twelve mature crossbreed mares (385 ± 47 kg live weight – LW) and 6 adult non-lactating cows (499 ± 36 kg LW) of Asturiana de los Valles breed were divided in groups of 3 animals and housed in individual stalls. Animals received a daily total amount of 1.0 kg DM/100 kg LW of different diets composed of herbaceous (Lolium perenne) and woody species (Ulex gallii and heather). Diet composition was estimated from LCFA (i.e., C 22 –C 34 ) and alkane (i.e., C 25 –C 31 and C 33 ) concentrations in diet and faeces by least-squares procedures, using marker faecal concentrations uncorrected for incomplete faecal recovery (FC0), corrected using mean recovery rate of the dietary treatment that the animal belonged to (FC1), or corrected using mean recovery rate across all experimental diets (FC2). For all diet components, LCFA concentrations were higher than the alkane ones, with even-chain LCFA accounting for more than 0.80 of total LCFA. In general, faecal recovery (FR) of the markers was incomplete and related to their carbon-chain length. In equines, the FR of both markers tended to decrease with carbon-chain length in a curvilinear fashion (P b 0.001), whereas in cattle LCFA and alkane FR tended to increase with carbon-chain length in a curvilinear (P b 0.001) and linear (P b 0.001) fashion, respectively. Diet composition had an effect (P b 0.001) on the LCFA and alkane FR in both animal species, and, in equines, seemed to be related with diet digestibility, i.e., decrease of marker disappearance from the digestive tract with a decrease of diet digestibility. In general, diet composition estimates based on LCFA alone were more accurate than those obtained using alkanes alone. Combination of LCFA and alkane markers resulted in an increase (P b 0.05) in the accuracy of diet estimates in both animal species, indicating a higher discriminatory power among plant species. The use of FC0 and FC2 resulted in the worst (P b 0.05) estimates of diet composition, while high levels of accuracy were observed when using more accurate faecal corrections (FC1). Results showed that LCFA can be useful markers for studying diet selection of equines and cattle grazing on heathland vegetation communities, if a proper adjustment of their faecal concentrations prior to their application is applied. It is also concluded that use of LCFA in combination with alkanes can increase the accuracy of diet composition estimates. © 2010 Elsevier B.V. All rights reserved. Keywords: Equines Cattle Long-chain fatty acids Alkanes Diet composition Heathland 1. Introduction Heathlands are shrubby vegetation communities wide- spread in the northwest of the Iberian Peninsula as a consequence of the abandonment of agricultural and live- stock managements initiated in the 1950s, and by frequent forest fires. Feral cattle and equines use these vegetation areas in free-ranging systems, generally in completely wild conditions with minimal management. In general, there is a lack of technical and scientific knowledge on how these herds behave (i.e., grazing paths, foraging behaviour, etc.) and their influence on the dynamics of the vegetation community. Livestock Science 131 (2010) 260–271 ⁎ Corresponding author. Tel.: + 35 1259350421; fax: + 35 1259325058. E-mail address: lmf@utad.pt (L.M.M. Ferreira). 1871-1413/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2010.04.011 Contents lists available at ScienceDirect Livestock Science journal homepage: www.elsevier.com/locate/livsci