Effect of conventional and extrusion pelleting on in situ ruminal degradability of starch, protein, and fibre in cattle

• Pelleting and cooking extrusion increased ruminal maize starch degradation
• Cooking extrusion increased ruminal maize starch degradability more than pelleting
• Pelleting and cooking extrusion decreased ruminal wheat starch degradation
• Pelleting and cooking extrusion decreased ruminal effective protein degradation
• Cooking extrusion increased ruminal effective NDF degradation

Rumen degradability kinetics was investigated for pelleted compound concentrates differing in physical functional properties of pellets. Six compound concentrate meals were produced containing either 100% wheat, 100% maize, 50% wheat+50% soybean meal (SBM; as is basis), 50% maize+50% SBM, 50% wheat+50% sugar beet pulp (SBP), or 50% maize+50% SBP. Meals were pelleted by either conventional pelleting, or by cooking extrusion using two distinct settings giving pellets with either high density (HD) or low density (LD). Ruminal degradation of starch, crude protein (CP) and NDF, and intestinal digestibility of CP were evaluated using in situ methods in cattle. Overall, processing (pelleting, extruding HD, or extruding LD) increased effective starch degradability (ESD) of pure maize and maize mixtures. The ESD increased with intensity of processing (Extruding LD>Extruding HD>Pelleting>Meal). In contradiction, ESD for pure wheat and wheat mixtures was reduced, though differences were minor. Conventional pelleting reduced the effective protein degradability (EPD) for pure wheat, but extrusion did not further affect the EPD. In contrast, the most intense processing with extrusion LD increased EPD for pure maize. Processing reduced EPD in both cereal+SBM mixtures, and further, the most intense processing with extruding LD led to the lowest EPD in cereal+SBM mixtures. In contrast, extruding increased EPD in both cereal+SBP mixtures as compared with meal and pelleting, but extruding with steam addition did not further increase the EPD. Compared to meal and pelleting, extruding without steam addition increased the effective NDF degradability for maize+SBP. The observed responses in EPD were not associated with decreases in CP disappearances from mobile bags. In conclusion, pelleting and extrusion affected ruminal degradability of starch, protein, and NDF differently depending on both type of cereal and composition of the concentrate mixture.