J. Anim Sci.
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J. Anim Sci. 1989. 67:2129-2139.
© 1989 American Society of Animal Science
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Effects of a Monensin Ruminal Delivery Device on Daily Gain, Forage Intake and Ruminal Fermentation of Steers Grazing Irrigated Winter Wheat Pasture1,2,

R. W. Davenport3, M. L. Galyean, M. E. Branine and M. E. Hubbert4

New Mexico State University, Las Cruces 88003

Abstract

Two trials evaluated the effects of a monensin ruminal delivery device (MRDD) on steers grazing winter wheat pasture. In Trial 1, 60 Hereford steers (initial wt 238.5 kg) grazed a 21.9-ha paddock of Vona-variety winter wheat for 112 d. Steers were assigned to either MRDD or control (C) treatments in a randomized complete block design. In Trial 2, eight ruminally cannulated steers (avg wt 234.4 kg) grazed a 2.4-ha paddock of Vonavariety wheat and were assigned randomly to either MRDD or C treatments. Three 11-d collection periods were conducted during early February, early March and early April. Chromic oxide was dosed to determine fecal output, and ruminal samples were collected on d 6 of each period. Nylon bags containing ground wheat forage were incubated ruminally beginning on d 8. In Trial 1, steers with MRDD tended (P < .11) to gain more weight than C steers (.44 vs .38 kg/d). In Trial 2, wheat forage intake, in situ DM disappearance, ruminal pH, ruminal ammonia concentrations and ruminal proportions of acetate and total VFA concentrations were not affected by treatment. Ruminal proportions of propionate were increased (P < .05) slightly by MRDD (20.3 and 19.2 mol/100 mol for MRDD and C, respectively). Butyrate proportions in ruminal samples were decreased (P < .05) by MRDD during March but not in other sampling periods. Ruminal fluid chlorophyll concentration was less (P < .05) for MRDD-treated vs C steers during early March but was greater (P < .10) for MRDD-treated steers during early April. The MRDD shows promise as a method of supplying monensin to cattle grazing winter wheat forage.

Footnotes

1 Journal article 1417 of the New Mexico Agric. Exp. Sta., Las Cruces. Appreciation is expressed to Lilly Research Laboratories, Greenfield, IN for supplying the monensin ruminal delivery devices and partial financial support and to Nolie Elliston for his assistance with the experiment.

2 Dept. of Anim. and Range Sci.

3 Present address: Livestock Advisory Services, Inc., P. O. Box 865, Friona, TX 79035.

4 Present address: Hoffmann-LaRoche, Inc., 6607 East County Road 60, Fort Collins, CO 80524.






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Copyright © 1989 by the American Society of Animal Science.