ARS | Publication request: Effects of Pendf and Starch Source on Digestibility and Ruminal Ph and Trunover in Dairy Cows

Submitted to: Journal of Dairy Science
Publication Type: Abstract
Publication Acceptance Date: April 12, 2004
Publication Date: July 25, 2004
Citation: Berzaghi, P., Mertens, D.R. 2004. Effects of peNCF and starch source on digestibility and ruminal pH and trunover in dairy cows. [abstract]. Journal of Dairy Science. 87(1):462.

Technical Abstract: The effects of ration physically effective NDF (peNDF) and starch source on ruminal characteristics and digestibility were investigated. A negative control (NC) diet, which contained 19% peNDF using finely chopped (TLC = 6.4 mm) corn silage as the main fiber source, was formulated to induce milk fat depression. Three diets were formulated to increase peNDF to 22% by adding about 9.5% finely chopped corn silage (CS), 12.2% chopped alfalfa hay (AH), or 6.7% chopped grass hay (GH) to NC. Diets for the four fiber sources were formulated with dry ground corn (DGC) or finely ground high moisture corn (HMC) to obtain eight diets that varied in starch source and peNDF source and concentration. Twenty-four cows were blocked for milk production and half were assigned to either DGC or HMC diets in replicated 4x4 Latin squares with 21d periods. One Latin square for starch source contained ruminally fistulated cows. Ruminal pH was measured for one day every three hours and rumen contents were manually evacuated before and after feeding and separated into solids and liquids. Fecal samples were obtained during the last week of each period. Indigestible NDF of feeds, ruminal contents and feces was determined by 240-h in situ incubation in all cows in the period following their collection. Mixed-model ANOVA indicated that NC and CS had lower (P<0.05) ruminal pH at 3-h post feeding, but similar average ruminal pH across diets. Rumen pool of DM and indigestible NDF (INDF) was not affected (P>0.05) by diet or starch source. However, turnover rate of INDF was increased (P<0.05) by the addition of AH and GH to the NC diet. Apparent DM digestibility (DMD) was not affected by starch source, but was highest for NC diet and lowest (P<0.01) for AH and GH. A positive relationship (r2=0.54; P<0.01) between retention time and DMD partially explained the differences in digestibility. In conclusion, dietary peNDF altered ruminal pH and affected DMD possibly by changes in retention time and associative effects.