Dietary selection and ingestive behaviour of fallow deer and sheep grazing on adjacent monocultures of white clover and tall fescue

The experiment compared dietary selectivity, in terms of both herbage intake and feeding behaviour, of fallow deer and sheep grazing on two types of pasture consisting of adjacent, one-area monocultures of Trifolium repens (C), at low standing mass availability (SM = 0.6 tDM ha(-1)) and compressed sward height (CSH =4.5 cm), and Festuca arundinacea (F) in two proportions by ground area: 25%C:75%F (pasture type 1) or 75%C:25%F (pasture type 2). A split plot design was carried out in two blocks, each comprising two 0.50 ha plots of different pasture type. Every plot was grazed sequentially by two herds of six 1-year-old animals of either Dama dama (live weight (LW) = 28.5 kg) or sheep (LW = 47.4 kg), for two consecutive 9-day grazing periods. A total of four herds were used, by moving over the herds grazing on the same type of pasture from block to block, at the end of the first grazing period. The grazing measurements were recorded on the last 3 days of every grazing period. The time spent grazing either grass or legume was evaluated from a visual scan of each animal, while dietary composition, herbage intake and digestibility were estimated by the n-alkane method, after correcting the faecal patterns of markers by their individual recovery, evaluated in a companion trial for fallow deer. Application of the n-alkane method provided an estimation of dietary selectivity, for both deer and sheep, coherent with well-established principles of herbivore nutrition. Indeed, under the conditions of vegetation geography and herbage abundance mentioned above, which would have allowed animals to gather monospecific diets on both pasture types, mixed diets were selected, largely dominated by the most extensive plant species. Deer grazed higher proportions of clover than sheep (53% versus 37%; P < 0.05) and displayed a preference for the legume, the inclusion of which tended to increase diet digestibility. In comparison with the lighter deer, sheep showed a higher total intake (1.62 kg DM d(-1) versus 1.12 kg DM d(-1); P < 0.01), thus attaining a comparable feeding level (90 g DM kg(-1)LW(0.75) versus 91 g DM kg(-1) LW-0.75) by consuming a greater amount of fescue at a higher rate of intake. On average, both ruminant species spent more time grazing on clover than fescue monocultures (257 min/d versus 164 min/d). The low SM and short CSH of clover introduced physical constraints which probably compelled animals to trade off their preferred diet with total daily herbage intake, resulting in a mixed diet with a lower proportion of clover than expected, particularly in the heavier and thus more demanding sheep. Deer exhibited longer nocturnal grazing activity, while sheep preferred afternoon and evening grazing, with little activity at night. (C) 2006 Elsevier B.V All rights reserved.