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.

Amino acid availability in ruminants of cereals and cereal co‐products

“…Differences in IED among AA and also among feeds should be determined by the concentration of indigestible components in RU, which in turn is conditioned by their concentration in the feed and its passive enrichment promoted by the ruminal fermentation . Thus IED results showed lower values in feeds with higher fibrous components (i.e.…”

“…These studies included two incubations of feeds in nylon bags in the rumen together with a transit study of the dietary concentrate particles in this compartment . Kinetics of dry matter (DM) degradation were establish by fitting to single‐exponential curves the DM disappearance recorded at times of 0 (non‐washout fraction), 2, 4, 8, 16, 24 and 48 h. Then the ruminal undegraded fraction (RU) of these feeds was determined in each wether from both these studies as indicated in Arroyo and González, considering both k c and k p rates. To correct for particle contamination with adherent microorganisms, a solution of N‐enriched ammonium sulfate was continuously infused into the rumen during this experimental phase and samples of solid adherent bacteria (SAB) were isolated and used as reference for these corrections.…”

“…All details on these procedures have been published previously . Effective estimates for AA of both RU and its intestinal digestibility (IED) were obtained from composite samples representative of the total rumen outflow of undegraded feed as proposed by Arroyo and González . Thus the freeze‐dried residues from both incubations were pooled in equal quantities for each animal and each incubation time.…”

“…However, the methodologies used in many of these assays have limitations biasing the results for the ruminal undegraded fraction and its intestinal digestibility. Thus AA availability studies have usually been performed using ruminal undegraded residues obtained at fixed incubation times, which do not represent the true ruminal residence time of feed particles . Therefore the resultant values do not consider either the undegraded AA flowing before this fixed time or those flowing after it due to subsequent ruminal protein degradation.…”

“…Therefore the resultant values do not consider either the undegraded AA flowing before this fixed time or those flowing after it due to subsequent ruminal protein degradation. In addition, the feed rumen residence has usually been under‐evaluated by considering only the rate of particle outflow from the rumen ( k p ) and not the time used in the process of particle conditioning necessary for this escape, which is represented by the particle comminution rate ( k c ) . Finally, in many of these studies the microbial contamination of feed particles in the rumen was not corrected in ruminal and intestinal estimates, in spite of the fact that this contamination may be important …”