Identifying feed characteristics that affect the pellet manufacturing of livestock diets containing different coproducts

As part of the transition to circular agriculture and to reduce food-feed competition for arable land, the inclusion of coproducts in livestock feed is expected to increase. Pellet manufacturing allows for improving the handling properties of livestock feed, but the effect of fibrous coproducts on the process is poorly understood. Inclusion of coproducts is considered to affect the physicochemical characteristics of a feed mash, and subsequently pellet manufacturing. To understand how coproducts can effectively be incorporated in pellet manufacturing, we investigated the effect of the inclusion of 300 g/kg of various fibrous coproducts, differing in fibrous composition, in feed mash containing 700 g/kg of basic mash, containing soybean meal, maize and soy oil, on mash physicochemical properties and pellet manufacturing. Treatment mashes were prepared in singleton, steam-conditioned and compacted using a ring-die pelletizer. Physical pellet quality, production capacity, and energy consumption of the pellet press were evaluated per treatment mash. Mash physicochemical properties were evaluated by determining hydration properties (i.e. water binding capacity and sorption analyses) and thermomechanical properties (i.e. phase transition and capillary rheometric analysis). Pellet durability varied among treatments (15.8–91.1 %), as did total energy costs of compaction (28.0–38.7 kWh/tonne). Principal component analysis indicated that higher levels of insoluble fibre in a feed mash associated with increased shear stress during capillary rheometric analysis. Combinedly these parameters reduced production capacity (R² = 0.25; P = 0.046) and increased required energy consumption by the pellet press (R² = 0.30; P = 0.03), but could only limitedly explain variation among treatments. In conclusion, the inclusion of coproducts with higher or lower levels of fibre did not consistently affect physical pellet quality. The overall low pellet durability (<90%) of all treatments, however, illustrates the challenge for the pellet manufacturing of diets containing fibrous coproducts. In addition the effects on energy costs of production should be considered during feed formulation.