title: Effects of the ruminal comminution rate and microbial contamination of particles on accuracy of in situ estimates of ruminal degradability and intestinal digestibility of feedstuffs.
abstract: Effects of considering the comminution rate (k(c) ) and the correction of microbial contamination (using (15) N techniques) of particles in the rumen on estimates of ruminally undegraded fractions and their intestinal digestibility were examined generating composite samples (from rumen-incubated residues) representative of the undegraded feed rumen outflow. The study used sunflower meal (SFM) and Italian ryegrass hay (RGH) and three rumen and duodenum cannulated wethers fed with a 40:60 RGH to concentrate diet (75 g DM/kgBW(0.75) ). Transit studies up to the duodenum with Yb-SFM and Eu-RGH marked samples showed higher k(c)  values (/h) in SFM than in RGH (0.577 vs. 0.0892, p = 0.034), whereas similar values occurred for the rumen passage rate (k(p) ). Estimates of ruminally undegraded and intestinal digestibility of all tested fractions decreased when k(c)  was considered and also applying microbial correction. Thus, microbial uncorrected k(p) -based proportions of intestinal digested undegraded crude protein overestimated those corrected and k(c) -k(p) -based by 39% in SFM (0.146 vs. 0.105) and 761% in RGH (0.373 vs. 0.0433). Results show that both k(c)  and microbial contamination correction should be considered to obtain accurate in situ estimates in grasses, whereas in protein concentrates not considering k(c)  is an important source of error.
authors: Departamento de Producción Animal, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid, Ciudad Universitaria, Madrid, Spain.
authors: J M
authors: JM
authors: Arroyo
authors: J
authors: J
authors: González
mesh_terms: D000818:Animals; D001419:Bacteria; D004063:Digestion / Q000502:physiology*; D006368:Helianthus / Q000382:microbiology*; D007422:Intestines / Q000502:physiology; D008129:Lolium / Q000382:microbiology*; D008297:Male; D010316:Particle Size; D012417:Rumen / Q000382:microbiology* / Q000502:physiology*; D012756:Sheep / Q000502:physiology*