Effect of conventional and extrusion pelleting on postprandial patterns of ruminal and duodenal starch appearance in dairy cows

Abstract Intra-ruminal mixing of separately fed pelleted compound concentrates differing in physical functional properties of pellets was investigated by measuring postprandial starch concentration in rumen medial contents and duodenal starch and protein appearance in dairy cows fed a basal diet low in starch. Four compound concentrate meals were produced containing either 100% wheat, 50% wheat + 50% soybean meal (SBM; as is basis), 100% maize, or 50% maize + 50% SBM. Compound concentrate 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). For each compound concentrate, a 3 × 3 Latin square digestibility test was conducted using three lactating Danish Holstein cows fitted with ruminal and duodenal cannulas, and the three pelletizing methods as treatments. Seven sample sets of rumen medial digesta and fluid, rumen ventral fluid, and duodenal digesta taken at -0.5, 0.5, 1.5, 2.5, 4.0, 5.5, and 7.0 h relative to separate allocation of experimental concentrates at 8.00 h were investigated. Low palatability was observed especially for LD pellets from cooking extrusion of the 100% grains as the pellets became sticky in contact with saliva and water. The rumen medial starch concentrations and fermentation variables did not differ among pelletizing methods in a clear manner across the four concentrate mixes investigated, as neither did fermentation variables in the rumen ventral contents. Except for 100% maize, the postprandial duodenal starch appearance was greater for conventional pellets as compared with other pellet types tested. The rumen outflow of crude protein did not differ among pelletizing techniques used for the four concentrates investigated. In conclusion, the current study indicated that concentrate pellets with differing physical functional properties had limited effects on the intra-ruminal mixing into the particulate mat. Yet, rumen escape of conventional pellets might be of a substantial magnitude if pellets with both high density and stability in liquid can be produced. Indeed, further investigations are needed.