THE CHEMICAL-COMPOSITION AND ENERGY VALUE OF HIGH-TEMPERATURE DRIED GRASS PRODUCED IN ENGLAND

The chemical composition, digestibility in vitro and in vivo and energy value in vivo of 22 high temperature dried, milled and pelleted grasses are reported. Prediction relationships between digestibility and metabolisable energy (ME) content and various laboratory measurements were also examined. The dried grasses were produced on five commercial drying plants throughout England over 4 years. They comprised 13 samples of early season and nine samples of later season material with 18 samples being based on perennial ryegrass and four on tall fescue. For the perennial ryegrass material there was a significant (P < 0.05 ) increase in the majority of cell wall fractions in the later compared with the early season samples although total cell wall content (measured as neutral detergent fibre) did not change significantly. Digestibility measured in vitro and in vivo was high but declined significantly (P < 0.01) between early and later season. Mean organic matter digestibility coefficients in vivo for early and later season were 0.78 and 0.73. Using predicted methane energy losses the mean ME contents were 11.5 MJ kg-1 dry matter (DM) and 10.3 MJ kg-1 DM, respectively. Higher levels of total ash in the later season material significantly contributed to the lower ME contents. The mean measured methane energy loss on a subset of nine samples was 0.061 of gross energy (GE) compared with 0.080 of GE predicted using a published relationship. Four samples of dried grasses based on tall fescue had higher contents of cell wall fractions and lower digestibility and energy values than those based on perennial ryegrass, although small numbers did not allow a statistical assessment of the differences. The mean ME contents of early and later tall fescue material were 9.2 MJ kg-1 DM and 9.4 MJ kg-1 DM using predicted methane energy losses. The best laboratory predictor of digestible organic matter content of the dry matter (DOMD) and ME was the enzymatic procedure based on neutral detergent-cellulase (NCD). The regression relationships were: DOMD (g kg-1 DM) = 59.9 + 0.828 NCD (g kg-1 DM), R2 = 90.4%, RSD = 15.2 ME (MJ kg-1 DM) = -0.59 + 0.0154 NCD (g kg-1 DM), R2 = 80.6%, RSD = 0.43.