Physical quality of pelleted animal feed 3. Contribution of feedstuff components

An overview is given of effects of the diet ingredients and their composition (e.g., starch, protein, sugar, fat and fibre content) on production characteristics of pellets and on their physical quality (pellet hardness and pellet durability) as compound animal feeds. Large differences exist in the effect on pellet physical quality within and between groups of diet ingredients when incorporated in pelleted animal diets. Differences in pellet quality between groups of diet ingredients, e.g., grains or legume seeds, can be attributed to differences in their physico-chemical properties which, in turn, are primarily affected by processing history, geographical and climatic origin and cultivar. Differences in physico-chemical properties due to the latter factors are also the main causative contributors to differences in pelleting quality (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 between groups with respect to pelleting properties and pellet quality, since their composition varies only within a relative narrow range. Because of the inherent variability of the raw materials, the effects of its constituents were investigated with respect to pellet quality. Effects of raw material constituents, both their level and physico-chemical properties, may provide more information on pelleting characteristics and pellet quality than the diet ingredient inclusion level of the raw material per se. The effects of starch (native versus gelatinized), sugar, protein (raw versus denatured), and solubility and resiliency of fibre are discussed with respect to pellet quality. When pellet hardness or durability is lacking, pellet binders may be used to improve pellet quality. The effects of pellet binders and their mode of action are discussed. Tt is concluded that more research effort should be directed towards the effects of individual constituents and their respective properties, since the latter seems to affect, to a large extent, the final hardness and durability of pelleted compound feeds. Moreover, the properties of a specific constituent reflects the processing history of that specific ingredient. By relating pellet quality to physico-chemical properties, e.g., functionality of the constituent, the manufacturer of compound animal feeds will be able to decrease the variability in final pellet quality caused by differences in geographical origin lid processing history of the diet ingredients. Objective criteria rom animals are still necessary to evaluate pellet quality as far as nutritional quality is concerned. (C) 1998 Elsevier Science B.V.