Rumen degradation and post-ruminal digestion of palm kernel by-products in dairy cows

Abstract

Rumen degradation characteristics and digestion post-rumen were measured in seven (five expellers and two meals) samples of palm kernel by-products using four cannulated (rumen and distal duodenum) dairy cows and nylon bag techniques. The by-products were selected to provide variation in chemical composition and in vitro digestibility. All samples contained high levels of cell wall constituents (70–80% of the fat-free organic matter) and 16–22% protein. The rumen undegradable fraction of neutral detergent fibre (NDF) varied between 23 and 37%; degradation of the NDF fraction was preceded by a lag phase, which was longest in the meals. Rumen degradation of the protein fraction was slow, especially for two Nigerian samples. The meals displayed larger fractions of rumen undegradable protein than the expellers. This fraction was satisfactorily predicted by a univariate relationship with in vitro digestion of protein (pepsin). Variation in protein degradation could not be satisfactorily accounted for by laboratory analyses using fungal proteolytic enzymes alone. The estimated high level of rumen escape protein may be partly attributable to microbial contamination. Post-ruminal digestion of the escape protein varied between 83 and 92% and correlated strongly with in vitro (pepsin) protein digestibility. Calculations suggest a slow rate of outflow from the rumen of both cell wall and protein constituents in palm kernel by-products.