title: Protein value of cereals and cereal by-products for ruminants: a comparison between crude protein and protein-based estimates.
abstract: In situ estimates of ruminal undegraded fraction (RU) and effective intestinal digestibility (EID, corrected for microbial colonisation) of dry matter (DM), crude protein (CP) and total analysed amino acids (TAA) of rye, wheat and corn grains, wheat bran, wheat and barley distillers' dried grains with solubles (DDGS) and corn gluten feed were measured on three rumen and duodenum cannulated wethers using (15)N labelling techniques and considering ruminal rates of particle comminution (kc) and outflow. Results indicate that not considering kc and microbial colonisation led to considerable overestimations of RU which increased with feed ruminal degradation. Microbial colonisation may be also associated with overestimations of EID, whose estimates for DM, CP and TAA were predicted from parameters related with the ruminal escape of intestinally indigestible materials. The RU estimates were higher for TAA than for CP in grains, but the opposite was observed in by-products, whereas EID estimates were higher for TAA in all feeds. To obtain accurate protein values in these feedstuffs, it is required to consider both kc and ruminal microbial colonisation. The CP-based results underestimate the intestinally digested protein in grains and the opposite is evidenced in cereal by-products. Microbial protein synthesised in the rumen is largely the major fraction of the feedstuff protein value with the exception of DDGS.
authors.affiliation: a Departamento de Producción Agraria, Escuela Técnica Superior de Ingenieros Agrónomos , Universidad Politécnica de Madrid, Ciudad Universitaria , Madrid , Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: González
authors.forename: Rabiaa
authors.initials: R
authors.lastname: Mouhbi
authors.forename: Jesús Alberto
authors.initials: JA
authors.lastname: Guevara-González
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: Rodríguez
authors.forename: José María
authors.initials: JM
authors.lastname: Arroyo
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001682:Biological Availability; D004032:Diet / Q000662:veterinary; D004063:Digestion; D002523:Edible Grain; D006041:Goats / Q000378:metabolism*; D008297:Male; D010940:Plant Proteins / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism*; D012418:Ruminants / Q000378:metabolism
chemical_list: D010940:Plant Proteins
keywords: feed evaluation; microbial contamination; protein digestibility; rumen digestion; sheep