Physically Effective Fiber: Method of Determination and Effects on Chewing, Ruminal Acidosis, and Digestion by Dairy Cows

Abstract

A study was conducted to investigate the effects of physically effective neutral detergent fiber (peNDF) content of dairy cow diets containing corn silage as the sole forage on intake, chewing, ruminal pH, microbial protein synthesis, digestibility, and milk production. A second objective was to compare current methods of measuring peNDF to determine the most suitable approach for use in ration formulation. The experiment was designed as a replicated 3 x 3 Latin square using 6 lactating dairy cows with ruminal cannulas. Diets varied in peNDF content (high, medium, and low) by altering the particle length of corn silage. The physical effectiveness factors (pef) and peNDF contents of the corn silage and diets were determined based on the original (19- and 8-mm sieves) and new Penn State Particle Separator (PSPS; 19-, 8-, and 1.18-mm sieves). A dry-sieving technique that measures the proportion of particles retained on a 1.18-mm sieve was also used. The new PSPS and the 1.18-mm sieve produced similar estimates of pef and peNDF of diets but gave higher values than the original PSPS. There was a much smaller range in pef of corn silage when 3 sieves, rather than 2, were used with the PSPS (range of 0.93 to 0.96 vs. 0.41 to 0.72, respectively). Consequently, increased forage particle length in the diets increased dietary peNDF content and its intake when using the original PSPS; however, the new PSPS and the 1.18-mm sieve failed to detect changes in dietary peNDF and peNDF intake. The peNDF values estimated based on fractional NDF rather than the total NDF content were higher, but the ranking of diets was not changed. Increased intake of peNDF linearly increased digestibility of CP and tended to linearly increase digestibility of fiber in the total tract. As a result, milk yield tended to linearly increase with no effect on milk composition. Ruminal microbial protein synthesis and microbial efficiency were higher with the medium peNDF than with the high or low peNDF diets. Total chewing time and ruminating time were linearly increased with increasing dietary peNDF, whereas influence of dietary peNDF on ruminal pH and fermentation was minimal. This study showed that increasing peNDF content of diets improved fiber digestion. Of the systems used to measure peNDF, the original PSPS provided a good description of dietary particle length and its effects on chewing time and rumen pH, whereas the new PSPS provided a more consistent chewing index, the ratio of total chewing activity to peNDF, across diets varying in chop length of corn silage.

Approche quantitative de l’aidose chez les ruminants

“…Il importe de chercher à traiter cette information avec les démarches et les méthodes statistiques adéquates afin DOI : 10.4267/2042/57937 de pouvoir continuer à progresser dans la connaissance de ce trouble et de mieux identifier les facteurs et les mécanismes impliqués. Depuis les années 2000, les synthèses publiées sur l'acidose ont pris un caractère quantitatif plus marqué (Martin et al 2006;Peyraud & Apper-Bossard 2006;Sauvant et al 2006;Sauvant & Peyraud, 2010;Yang & Beauchemin, 2006 …”

Effects of different levels of physically effective fibers in diets for cows in early lactation

“…Similarly, no difference in PEF was found for long (22.3 mm) and short (4.8 mm) cut corn silage in the study by Kononoff & Heinrichs (2003b). Yang & Beauchemin (2006a) determined greater range in PEF using original PSPS with two sieves, than those obtained using three sieves (range of 0.41-0.72 vs. 0.93 to 0.96, respectively) for three theoretical cut length of corn silage (28.6, 15.9 and 4.8 mm).…”

“…In this study, proportion of concentrate in the diets for different treatments was approximately 57% in DM basis. Reduced chop length of CS (Kononoff & Heinrichs, 2003b;Yang & Beauchemin, 2006a), and AH (Yang & Beauchemin, 2007) did not affect the dietary DM and NDF intake. It was discussed that the different dietary content of PENDF did not affect the rumen rate of digesta passage and thereby DM intake (Beauchemin & Yang, 2005).…”

“…Lower digestibility of NFC with the reduced particle lengths of CS and AH is probably the result of an ab-sence of shift in starch digestion from the rumen to the intestine, which is typical for rations with longer cut forages (Yang & Beauchemin, 2006a). The reduced dietary particle size might increase the rates of the "small size particle" ruminal passage, reduced ruminal starch fermentation, and increased outflow of starch into intestine.…”

“…The concept of physically effective fiber (PENDF) takes into account the dietary particle size and NDF (neutral detergent fiber) content of the diet, and defines physical effectiveness of the diet (Mertens, 1997). Yang & Beauchemin (2006a concluded that using Penn State Particle Separator (PSPS) provided a good description of forages and dietary physical effectiveness of the diets.…”