Assessing fibre-rich feedstuffs in pig nutrition: comparison of methods and their potential implications

BACKGROUND: In organic farming, roughage has to be added to pigs' daily rations for animal welfare reasons. Since little is known about how roughage affects pigs, seven carbohydrate-rich feedstuffs (corn silage, ryegrass, turnip leaf, turnip tuber, Jerusalem artichoke and two types of clover-ryegrass silage) were tested using two different in vitro methods - total tract digestibility and the gas production technique - to determine apparent digestibility by observing organic matter loss. The aim was to determine whether the results of different methods and treatments lead to similar results or rankings. RESULTS: The in vitro enzymatic incubation method showed 3-20% lower fermentabilities than the in vitro fermentation process. The pretreatment of substrates with enzymes before fermentation led to similar fermentabilities but different gas production kinetics compared to the fermentation of untreated substrates. Using two different inocula generated no significant differences. When the feedstuffs were ranked by their fermentability, the rank order was relatively similar for both methods. CONCLUSIONS: Different methods and pretreatments lead to different fermentabilities while a ranking of the results gives a similar order. Both methods seem to be appropriate tools for assessing feedstuffs. In order to determine which feedstuff is best utilised by the animal, further investigations of both digestibility and gas production kinetics are required