Use of n-alkanes and long-chain alcohols as faecal markers to estimate diet composition on small ruminants grazing/browsing mountain grasslands

• Autor(a) principal: Magalhães, Rui José Ribeiro Ferreira de
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10348/8394
• topic: alcanos; álcoois de cadeia longa; composição da dieta; pequenos ruminantes; pastoreio

Knowledge on the grazing/browsing behaviour, especially diet selection, of the different domestic herbivorous species under diverse vegetation communities is of particular importance for the development and application of appropriate grazing management strategies that increase the efficiency of the utilization of the existing vegetation and, consequently, the sustainability of the animal production system. Plant-wax components, namely alkanes and long-chain alcohols (LCOH), have been suggested as faecal markers to estimate diet selection of different ruminant and non-ruminant species. By combining these two marker types, it is possible to obtain a more specific “fingerprint” for each particular plant species, making it possible to obtain more accurate estimates of diet composition. The main objective of this master thesis was to assess the combination of n-alkanes and LCOH to estimate diet composition of the domestic herbivorous species in a field study. Additionally, effect of using different calculation approaches (using all individual plant species or grouping plant species with similar marker profiles) and faecal recovery data on diet composition estimates was also assessed. To study these hypothesis, thirty-thee ewes and thirty-five does were managed in a plot established on a natural shrubland of heather-gorse with an adjacent area of improved pasture. Samples from all the plant species identified in the grazing area and faecal samples of twelve ewes and fourteen does were collected and analysed for their n-alkanes and LCOH patterns. Two different approaches were applied to determine the diet composition: A1 (using all the plant species available as possible diet components) and A2 (grouping plant species according to the results obtained from the cluster analysis). The approach used significantly affected the diet composition obtained in sheep. When using the A1 approach, the proportion of U. galli in sheep diet was higher than the values reported previously for sheep grazing the same vegetation conditions, whereas the proportion of L. perenne was lower than expected. The A2 approach decreased the proportion of U. galli significantly to values closer to the ones reported in previous studies, whilst the proportion of grass species increased to levels closer to the ones expected. The approaches used did not have an effect on the diet composition estimates of goats. The proportion of U. galli was higher than the values reported previously for goats grazing the same vegetation communities, whereas the values for herbaceous species were lower. The faecal recovery values used had no effect on the diet composition estimates of sheep whereas for goats there was a significant effect. Overall, the results show that the combine use of n-alkanes and LCOH as faecal markers produced accurate estimates of the diet composition of sheep when the A2 approach was used. For goats, it was not possible to obtain accurate diet composition estimates for both approaches. The utilizations of more information (direct observation, application of microhistological procedures) on the grazing behaviour of the individuals and increasing the number of markers used in the calculations are two possible solutions that can be used to improve the accuracy of diet composition estimates.