Foraging behaviour of domestic herbivore species grazing on heathlands associated with improved pasture areas

Abstract

Foraging behaviour (grazing time, diet selection) and overlap in vegetation use between five beef cows, five mares, 32 ewes and 32 does, suckling their offspring born in late winter–early spring, was compared across the grazing season (May–December). Animals were managed in mixed grazing on heather–gorse vegetation communities with an adjacent area (24%) of ryegrass–clover improved pasture. Equines spent more daily time grazing than the other species in all seasons, averaging 610min/day compared to 530, 481 and 496min/day spent by cattle, sheep and goats, respectively. Seasonal changes in both grazing behaviour and diet selection were observed. Generally, cows, mares and ewes spent most of their grazing time on the improved pasture (0.77, 0.73 and 0.59, respectively), whereas goats spent more time grazing on shrublands (0.70). All species concentrated their diurnal grazing activity in the morning and late afternoon, whilst resting occurred mainly in the middle of the day. Herbaceous species were the main component in the diets of cattle, equines and sheep across the whole grazing season, whereas for goats this predominance was only observed during the spring. Cattle, sheep and equines turned to browse only when pasture availability decreased. Cattle and sheep tended to select heather in moderate amounts whereas they avoided gorse across the grazing season. By contrast, horses seemed to be able to deal with the gorse spiny shoots and consumed it in the autumn (averaging 0.29). The goats' diet at the end of the grazing season was mainly composed of heather species, reaching 0.81 in November. Degree of grazing overlap between livestock species was influenced by the animal species and also varied across the grazing season. The greatest similarity indexes (KSI) based on grazing time and diet composition data were found between cattle and equines (0.86) and between cattle and sheep (0.94), whereas the combination of goats with the other animal species resulted in lower KSI values. Dietary overlap decreased as the improved pasture availability decreased during the grazing season. Results suggest that the success of management strategies (type and composition of the flock, mixed or sequential, continuous or seasonal) in these heterogeneous vegetation conditions will depend on plant species characteristics and its proportions. Grazing management options should be based on production (animal performance) or environmental goals (biodiversity, control of shrub encroachment, reduction of fire risk, etc.) previously defined. Goats proved to be the best complement to the other animal species for an efficient use of natural vegetation. Nevertheless, studies should be carried out to assess the interactions between grazing behaviour and animal performance in these particular vegetation conditions.