Relations between Ad Libitum Intake of Several Forage Species and Gut Fill

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Abstract
Wethers receiving several forages were slaughtered and their rumen contents examined to ascertain the relationships between dry matter (DM), cell wall constituents (CWC), fiber and lignin content and ad libitum consumption. Intake of DM, fiber and lignin was higher (P<.05) for sheep receiving alfalfa and trefoil compared with bromegrass and canarygrass. Rumen digesta from sheep receiving the legumes tended to contain larger amounts and a larger percent of fiber and lignin than those receiving bromegrass or canarygrass. Lignin content of the forages or total intake of fiber or lignin did not appear to limit consumption. DM and CWC in the rumen 6 hr. after feeding did not appear to be related to ad libitum DM intake. DM and CWC in the rumen 12 hr. after feeding may be related to DM intake of sheep receiving forage at 12-hr. intervals. However, the relation between amount of DM in the rumen and intake was not clear-cut and indicated that there probably were other factors playing a role in controlling ad libitum intake of high quality hays. Rumen retention time of DM was about 0.65 days for legumes and 1 day for grasses. Rumen retention time of lignin was greater (P<.05) than that of fiber, and fiber retention time tended to be greater than that of DM. Average retention time of CWC appeared to be about the same as that of DM. As DM, fiber and lignin intake increased, retention time of each constituent decreased. Further studies on the above relation are necessary to separate cause and effect. Calculated removal rate of DM, CWC, fiber and lignin from the rumen during 1 to 6 and 6 to 12 hr. postprandial indicate some differences among the different forages. Rumen digesta from sheep fed alfalfa contained a higher (P<.05) concentration and molar percent of butyrate than that of sheep fed canarygrass. Concentration of acetate, propionate and butyrate in rumen digesta was greater (P<.05) at 6 hr. than at 12 hr. postprandial; however, there was no significant difference in molar percent of VFA's between the two time intervals. The decrease in concentration of acetate and propionate from 6 to 12 hr. postprandial tended to be greater for legumes. Copyright © 1966. American Society of Animal Science . Copyright 1966 by American Society of Animal Science