Impact of diet selected by cattle and sheep grazing heathland communities on nutrient supply and faecal micro-flora activity

In the UK the funding mechanism for moorland restoration is implemented primarily through agri-environment schemes, yet comparatively little is known of the nutritional consequences of selecting diets from semi-natural vegetation communities. In this study the feed intake and diet digestibility of four groups of animals grazing heathland swards with low (8%) and high (61%) percentages of cover of Calluna vulgaris were estimated using n-alkanes. The impact of diet choice on metabolic status was monitored through blood sampling, and complementary in vitro studies investigating species/breed differences in gut microbial populations were carried out using faecal samples. Two breeds of sheep (Welsh Mountain (WM) and Scottish Blackface (SBF)) and two breeds of cattle (Welsh Black (WB) and Continental cross (CX)) grazed the experimental sites during two separate 14-day sampling sessions, in July and September, respectively. Between-species and between-breed differences in intake and diet digestibility were recorded. Chemical analysis of the main sward components highlighted the poor nutritional value of heathland species to ruminants, with most major plant groups having crude protein concentrations of less than 100gkg⁻¹ DM and digestible organic matter in the dry matter values of 0.400-0.500gg⁻¹. Overall, the blood metabolite results indicate that the intake of both energy and protein was less than optimal to supply even maintenance requirements. Low dietary protein intakes were linked to low serum urea concentrations in all animals. The serum non-esterified fatty acid concentrations indicated a feed energy deficit for both sheep and cattle, with the data suggesting that the deficit was greater for cattle than for sheep. While differences in diet composition could be linked to differences in metabolic profile, diet selected had little apparent impact on faecal micro-floral characteristics, with the gas production data indicating very few significant differences in the activity of microbial populations between different breeds of the same species. Overall the results demonstrate that careful management is required when domestic livestock graze such swards if animal welfare is not to be compromised. They also highlight the poor production potential of such vegetation communities, and the related repercussions with regards to economic sustainability.