Feeding value, in vitro digestibility and in vitro gas production of different by-products for ruminant nutrition

Nine by-products used in animal nutrition were examined for their nutritive value by determining the chemical composition (crude protein, crude fat (ether extract), neutral detergent fibre, acid detergent fibre, lignin), in vitro organic matter digestibility and rumen fermentation kinetics (from gas production curves measured in vitro). The by-products studied were giant pumpkin, red pepper, stem broccoli, brewer's grain, fresh artichoke, scalded artichoke, lemon peel, orange peel and melon. The nutritive value was very variable, depending on the by-product and on the process applied to the material during industrial processing. In vitro gas production was measured for 500 mg dry matter in quadruplicate at 39degreesC after 6, 12, 24, 36, 48 and 72 h of incubation and fitted to single-pool exponential equations. The fermentation kinetics indicated that brewer's grain was the only by product which fitted well with the p = a + b(1 - e(-ct)) equation model; all other by-products had a very fast degradation rate and their gas production fitted the equation p = b(1 - e(-c(t-L))), because in the other exponential model a was negative. (C) 2002 Society of Chemical Industry.