Site and Extent of Neutral Detergent Fiber Digestion, Efficiency of Ruminal Digesta Flux and Fecal Output as Related to Variations in Voluntary Intake and Chewing Behavior in Heifers

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Abstract
Six heifers (1/4 Brahman × 1/4 Jersey × 1/2 Angus, 290 kg avg wt) with ruminal, duodenal and ileal cannulas were given ad libitum access to a corn silage-based diet with or without 100 mg monensin·hd−1·d−1 in a two-period crossover design. There was no significant effect of monensin on voluntary intake (VI), flow of NDF to the abomasum, fecal output or the efficiency of transfer of NDF to the duodenum (unitary fluxes of NDF through the reticulo-omasal orifice, number·g NDF·(kg BW.75)−1). Monensin increased extent of NDF digestion (NDFD) in the dorsal (P = .07) and ventral (P = .09) ruminal sac. As a fraction of the total tract NDFD, NDFD increased progressively in dorsal rumen (.214), ventral rumen (.548) and duodenal (.818) sites. The VI among individual heifers was negatively related to unitary fluxes of NDF through the reticulo-omasal orifice (P = .001) and to the extent of digestion of potentially digestible NDF (PDNDFD) in the ventral rumen (P = .006) and duodenum (P = .032), but not in the dorsal rumen (P = .720) or in the total tract (P = .785). Fecal output of NDF was negatively related to unitary times of eating (P = .027), ruminating (P = .001), masticating (P = .001) and unitary number of rumination boli (P = .001). These relationships all were influenced (P = .001) by individual heifer. The results suggest that heifers with higher VI vs heifers with lower VI had greater efficiency (lower unitary activity) of chewing, flux of NDF through the reticulo-omasal orifice, and less PDNDFD in their forestomach with compensatory greater PDNDFD in their cecum-colon. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science