Evaluation of counts of ruminal fibrolytic bacteria and enzyme activities in response to corn silage particle size in high-yielding dairy cows. (Abstract)

Publication Type

Contribution to conference

Authors

Zebeli, Q., Ölschläger, V., Tafaj, M., Vahjen, W., Junck, B., Simon, O. and Drochner, W.

Year of publication

2007

Published in

J. Anim. Sci. Vol. 85 Suppl. 1/ J. Dairy Sci. Vol. 90 Suppl. 1/ Poultry Sci. Vol. 86 Suppl. 1

Editor

ADSA - PSA - AMPA - ASAS

Series/labeling

Annual meeting

Page (from - to)

618-619 (Nr. 791)

Conference name

2007 Joint Annual Meeting

Conference location

San Antonio, TX, USA

Conference date

08.-12.07.2007

Keywords

dairy cow, fibrolytic bacteria, ruminal fermentation

This study examined the effects of particle size (PS) of corn silage (CS) on counts of selected fibrolytic bacteria and related enzyme activities in particulate or fluid ruminal digesta as well as on ruminal or total digestive tract fiber degradation in dairy cows fed TMR (40% CS, 10% hay and 50% cereal-based concentrate; DM basis) ad libitum. Four early-lactating (67 ± 8 DIM), rumen-fistulated Holstein cows were randomly assigned to incomplete block switch-back design in four 23 -d periods to 1 of 3 diets (in average: 6.9 MJ NEL/kg of DM, 15% CP and 35% NDF in DM) differing in PS of CS: 14, 8.1 and 5.5 mm (n=5/treatment). After a 12-d diet adaptation, digesta samples were collected from dorsal (particulate) and ventral (fluid) rumen sac, 1 h before and 3 h alter morning feeding, and analyzed for pH, VFA, fibrolytic enzyme activities (by an agar-diffusion assay) and counts of fibrolytic bacteria using 16S rDNA quantification by real-time PCR. In general, the counts of total eubacterial cells, R. albus and R. flavefaciens were not affected by dietary PS (P>0.10), but the activities of CMCase, Glucanase, Galactanase and Xylanase quadratically increased with reducing PS (P<0.05). This was reflected in quadratically increased ruminal (in situ: P = 0.07) or total tract (P<0.05) fiber degradation. Decreasing dietary PS did not affect ruminal pH (P>0.10), but increased ruminal C2/C3 ratio and C4 proportion (P<0.05). Compared to fluids, the particulate digesta showed higher counts of fibrolytic bacteria and enzyme activities (P<0.05), whereas the latter were stronger enhanced by reducing dietary PS (P<0.05). Results of this study indicate that reducing PS of CS in a TMR has the capacity to increase fiber degradation in the rumen of dairy cows, particularly by stimulating the activities of fibrolytic enzymes rather than increasing the total count of fibrolytic bacteria.