PHYSICAL QUALITY OF PELLETED ANIMAL FEED 3 - CONTRIBUTION OF FEEDSTUFF COMPONENTS

An overview is given of effects of the diet ingredients and their comp osition (e.g., starch, protein, sugar, fat and fibre content) on produ ction characteristics of pellets and on their physical quality (pellet hardness and pellet durability) as compound animal feeds. Large diffe rences exist in the effect on pellet physical quality within and betwe en groups of diet ingredients when incorporated in pelleted animal die ts. Differences in pellet quality between groups of diet ingredients, e.g., grains or legume seeds, can be attributed to differences in thei r physico-chemical properties which, in turn, are primarily affected b y processing history, geographical and climatic origin and cultivar. D ifferences in physico-chemical properties due to the latter factors ar e also the main causative contributors to differences in pelleting qua lity (e.g., throughput, energy consumption of the pellet press) within groups (e.g., cereals or legume seeds); thus, in the resulting pellet quality. Raw materials within one group are much more the same than b etween groups with respect to pelleting properties and pellet quality, since their composition varies only within a relative narrow range. B ecause of the inherent variability of the raw materials, the effects o f its constituents were investigated with respect to pellet quality. E ffects of raw material constituents, both their level and physico-chem ical properties, may provide more information on pelleting characteris tics and pellet quality than the diet ingredient inclusion level of th e raw material per se. The effects of starch (native versus gelatinize d), sugar, protein (raw versus denatured), and solubility and resilien cy of fibre are discussed with respect to pellet quality. When pellet hardness or durability is lacking, pellet binders may be used to impro ve pellet quality. The effects of pellet binders and their mode of act ion are discussed. Tt is concluded that more research effort should be directed towards the effects of individual constituents and their res pective properties, since the latter seems to affect, to a large exten t, the final hardness and durability of pelleted compound feeds. Moreo ver, the properties of a specific constituent reflects the processing history of that specific ingredient. By relating pellet quality to phy sico-chemical properties, e.g., functionality of the constituent, the manufacturer of compound animal feeds will be able to decrease the var iability in final pellet quality caused by differences in geographical origin lid processing history of the diet ingredients. Objective crit eria rom animals are still necessary to evaluate pellet quality as far as nutritional quality is concerned. (C) 1998 Elsevier Science B.V.