The chewing behaviour of red deer (Cervus elaphus) during eating and the effectiveness of chewing on feed comminution was studied in two experiments. In Expt 1, deer were fed long or chopped lucerne (Medicago sativa) hay, and feed intake and chewing activity were recorded. In Expt 2, the rumen was emptied and test meals of fresh chicory (Cichorium intybus cv. Puna), lotus (Lotus corniculatus cv. Grasslands Goldie), ryegrass (Lolium perenne cv. Ruanui) forage and long lucerne hay were given, chewing activity recorded and the ingested forage quantitatively removed from the rumen. In Expt 1, the chopped hay was eaten more quickly than long hay (11·4 v. 8·3 g dry matter/min), and required fewer chewing bites per g dry matter eaten. In Expt 2, the four forages were consumed at similar rates (mean 4·3 g organic matter/min) and there was no significant difference in the chewing required to consume either total organic matter (OM) or cell wall OM. Deer chewed more quickly when eating lucerne hay than when eating lotus, and it was estimated that a greater number of chewing bites were required to form a bolus of lucerne hay than to form a lotus bolus. The proportion of ingested OM which was comminuted so as to pass a 1 mm sieve (efficiency of chewing) was greater for lotus (0·485) and lucerne hay (0·.518) than for chicory (0·.267). The efficiency of chewing ryegrass (0·.366) was intermediate and not significantly different from any other forage. For all forages, the main effect of chewing during eating appeared to be the release of cell contents, rather than the comminution of cell wall. Physical breakdown to particles which passed a 1 mm screen but were retained on an 0·25 mm screen was low for fresh forages (0·074–0·086) but was slightly higher for lucerne hay (0·127). Deer reduced feed particle size during eating with a similar efficiency to sheep, but were less efficient than goats.
It is suggested that the chewing effort associated with forage consumption by red deer is related to the need to form a bolus. The amount of chewing may be as much influenced by the physical characteristics of the forage (e.g. leaf size and shape) as by its chemical composition, and the extent of comminution during eating may be determined by the processing needed to form a bolus and the resistance of the feed to bolus formation.