Pure swards of chicory (Cichorium intybus) and perennial ryegrass (Lolium perenne) were grown at Palmerston North, New Zealand. They were cut daily and fed hourly at 2·25 kg dry matter (DM)/day to eight hand-reared, rumen-fistulated castrated red deer stags kept in metabolism crates during December 1994 and January 1995 (summer). Apparent digestibility, rumen fractional disappearance rate (FDPR), rumen fractional degradation rate (FDR), rumen fractional outflow rate (FOR) and mean retention time (MRT) were measured. The ratio of readily fermentable carbohydrate to structural carbohydrate was approximately three times higher in chicory than in perennial ryegrass. Apparent digestibility of DM was higher in deer fed chicory than in deer fed perennial ryegrass (0·785 v. 0·727), whilst apparent digestibility of neutral detergent fibre (NDF) was lower in deer fed chicory (0·679 v. 0·755), due to a reduced hemicellulose digestibility (0·667 v. 0·783). Relative to deer fed perennial ryegrass, those fed chicory had higher rumen FDPR values for DM (14·5 v. 8·6%/h), soluble carbohydrate (69·9 v. 54·7%/h), cellulose (15·5 v. 9·8%/h) and lignin (6·8 v. 3·8%/h). Rumen FDR in deer fed chicory was higher than those fed perennial ryegrass for cellulose (11·4 v. 7·0%/h) and lignin (2·7 v. 1·0%/h), but tended to be lower for hemicellulose. Rumen FOR was higher and MRT was lower for both liquid and particulate matter in deer fed chicory compared to deer fed perennial ryegrass.

It is concluded that rumen FDPR and apparent digestibility were much higher in deer fed chicory than in deer fed perennial ryegrass, due to faster degradation rates of most constituents in the rumen and faster outflow rates from the rumen. An exception was hemicellulose, where reduced rumen degradation rates and shorter rumen particulate MRT contributed to reduced apparent digestibility. Faster clearance from the rumen, due to both faster degradation and outflow rates may be used to explain the greater voluntary feed intake (VFI), as well as faster growth rate in deer grazing chicory compared to those grazing perennial ryegrass. Faster rates of lignin solubility in the rumen probably contributed to the more rapid breakdown of chicory in the rumen.