The Effect of Varying Levels of Monensin in Finishing Rations for Beef Cattle Special Report 452 January 1976 Agricultural Experiment Station Oregon State University, Corvallis
AUTHORS: A. T. Ralston, professor of animal nutrition, and T. P. Davidson, superintendent, Umatilla Branch Station, Columbia Basin Agricultural Research Center, Oregon State University. ACKNOWLEDGMENT: Research supported in part by Elanco Products Company, a division of Eli Lilly and Co.
THE EFFECT OF VARYING LEVELS OF MONENSIN IN FINISHING RATIONS FOR BEEF CATTLE A. T. Ralston and T. P. Davidson SUMMARY One hundred twenty steers were fed Monensin at either 0, 50, 100, 200 or 300 mg per head daily. The 50 mg level increased average daily gains with an accompanying improvement of feed efficiency by 5%. Improvement of feed efficiency was not as great on a barley-based diet as reported on typical corn diets apparently due to less change in the acetate:propionate ratio of volatile fatty acids. At levels above 50 mg there was a palatability problem which reduced feed intake. INTRODUCTION Monensin is a coccidiostatic antibiotic produced by Streptomyces cinnamonensis and first reported by Haney and Hoehn (1967). In the screening of coccidiostats to control bovine coccidiosis, Raun et al (1974) reported that the acetate:propionate ratio was narrowed. Earlier work of Hungate (1966) had shown that propionic acid is more efficiently used for growth or fattening then acetate by the host animal. Furthermore, Leng et al (1967) had shown propionic acid to have a protein sparing effect. This was due to the ruminant obtaining a portion of its glucose needs from proteins (Reilly and Ford, 1971) and propionic acid is a precursor of glucose. With the increased feed costs *and the reduced value of finished beef, anything than can improve feed conversion should be of importance to feedlot operators.
2 METHODS One hundred twenty yearling steers (800-900 lbs) were divided into a heavy and a light group by weight. Within each group they were stratified as to weight and randomly allotted to 1 of 5 pens (5 pens of heavy cattle and 5 pens of light cattle of 12 steers per pen). All steers received the same finishing ration on an ad libitum basis (table 1). In addition, each animal received 1 lb of an OSU 40% protein supplement per head daily (table 2). Monensin was added to the protein supplement at the rate of 0, 50, 100, 200 or 300 mg per pound. This resulted in a light and heavy replicate of each level of monensin. Individual weights were taken at 28-day intervals, throughout the trial. Pen feed intake and pen feed efficiencies were measured and rumen samples were taken from three representative steers from each pen. Volatile fatty acids were measured at Lilly Research Laboratories by gas chromatographic techniques. The steers were slaughtered at 1200 and 1300 lbs live weight. Carcass information including warm carcass weight, carcass conformation, marbling score, USDA grade, backfat and estimated yield of trimmed cuts was recorded. RESULTS Monensin did not significantly improve average daily gain. The 50 mg level of monensin produced significantly (P<.05) greater gains than the 300 mg level. Although not analyzed statistically, the 50 mg level produced the most efficient gains. Apparently monensin was not very palatable since levels above 50 mg caused a reduction in feed intake. Similar results in
3 intake were noted in a simultaneous trial by Dyer of Washington State University. The modest improvement in feed efficiency at the 50 mg level was approximately 5%. This amounted to a saving of 184 lbs of feed per steer as compared to the controls. At $6/cwt of feed it represents $11/steer. There were no significant differences in carcass characteristics due to treatment (table 4). The feed saving in Washington and Oregon was not as high as reported in the Midwest. A possible reason was a difference in the grain used in the ration. Only at the higher level (300 mg per head daily) was the percent of propionate actually increased (table 5). On many barley-based diets the acetate:propionate ratio is close to 1:1, whereas, acetate: propionate ratios of corn-based diets are closer to 5:3. As might be expected from the differences in the volatile fatty acid (VFA) ratios from differing rations, the greatest increase in feed efficiencies on corn-based rations was produced at the 300 mg per day levels (Raun et al, 1974). Monensin has been reported to be as effective on pasture as it was in the feedlot'(potter et al, 1974). Under pasture conditions there was a narrowing of the acetate:propionate ratio at all levels of monensin.
4 LITERATURE CITED Dyer, I. A. 1974. Personal communication. Haney, Jr., M. E. and M. M. Hoehn. 1967. Monensin, a new biologically active compound. I. Discovery and isolation. Antimicrobial Agents and Chemotherapy. p. 349. Hungate, R. E. 1966. The Rumen and Its Microbes. Academic Press. Leng, R. A., J. W. Steel and J. R. Luick. 1967. Contribution of propionate to glucose synthesis in sheep. Biochem. J. 103:785. Potter, E. L., C. 0. Cooley, A. P. Raun, L. F. Richardson and R. P. Rathmacher. 1974. Effect of monensin on daily gain of cattle on pasture. Proc. West. Sec. Amer. Soc. Anim. Sci. 25:343. Raun, A. P., C. 0. Cooley, R. P. Rathmacher, L. F. Richardson and E. L. Potter. 1974. Effect of different levels of monensin on feed efficiency ruminal and carcass characteristics of cattle. Proc. West. Sec. Amer. Soc. Anim. Sci. 25:346. Reilly, P. E. B. and E. J. H. Ford. 1971. The effects of dietary contents of protein on amino acid and glucose production and the contribution of amino acids to gluconeogenesis in sheep. Brit. J. Nutr. 26:24.
5 TABLE 1. COMPOSITION OF THE BASAL RATION* Ingredients Percent Steam rolled barley 83 Beet pulp 10 Molasses 5 TM salt 1 Oyster shell flour, ad libitum 1 40% Protein supplement** 1 *Approximately 10% crude protein and 77% total digestible nutrients. **Fed one pound per head daily. TABLE 2. COMPOSITION OF OSU 40% PROTEIN SUPPLEMENT Ingredient Percent Urea 7.0 Cull peas 73.0 Dehy alfalfa 5.0 Cottonseed meal (41%) 10.0 Limestone - 2.0 Tricalcium phosphate 2.0 Vitamin A (10,000 IU/g).5 Trace mineralized salt.5
6 TABLE 3. EFFECT OF MONENSIN ON FEEDLOT PERFORMANCE Treatment mg/head daily Days on feed Initial wt., lbs. Plant wt., lbs. Daily ADG feed lb. eaten a lb. Lbs. of feed/cwt. gaina 152 900 1301 2.67 20.75 6.63 152 800 1229 2.82 20.70 7.51 Average 152 850 1266 2.75bc20.72 7.07 50 151 905 1351 2.95 22.44 6.36 152 800 1232 2.84 19.47 6.87 Average 151 852 1292 2.90b 20.95 6.61 100 152 899 1312 2.72 20.53 7.38 152 799 1192 2.59 18.07 7.10 Average 152 849 1252 2.66bc19.30 7.24 200 152 905 1322 2.74 19.43 7.53 152 800 1219 2.76 17.42 6.99 Average 152 852 1271 2.75 bc 18.42 7.26 300 152 904 1281 2.48 19.27 7.70 152 799 1178 2.49 17.30 6.70 Average 152 851 1230 2.49c 18.28 7.20 b:jigures in these columns are pen averages. Averages with differing superscripts were significantly different (P.05).
7 TABLE 4. EFFECT OF.MONENSIN ON CARCASS CHARACTERISTICS Treatment mg/head daily Warm wt., lbs. Confl MS 2Grade3 BF (in.) Yield 0 769 17.6 12.6 15.8.6 49.1 725 17.5 14.3 16.0.6 48.6 Average 747 17.5 13.4 15.9.6 48.9 50 797 17.6 ' 14.0 16.0.7 48.5 727 17.7 12.3 15.5.6 48.7 Average 757 17.6 13.1 15.7.6 48.6 100 774 17.4 13.6 15.8.6 48.5 703 17.4 13.0 15.6.5 49.1 Average 738 17.4 13.3 15.7.5 48.8 200 780 17.3 13.5 15.8.6 48.9 719 17.0 11.5 15.5.5 49.3 Average 749 17.1 12.5 15.6.5 49.1 300 756 17.5 13.3 15.6.6 48.7 695 17.1 11.8 15.5.5 49.0 Average 725 17.3 12.5 15.5.5 48.8 'Conformation 14 = average good, 17 = average choice 2Marbling score 12 = average small, 15 = average modest, 18 = average moderate 3 Grade 14 = average good, 17 = average choice
8 TABLE 5. EFFECT OF MONENSIN ON MOLAR PROPORTIONS OF VFA'S IN RUMEN CONTENTS OF CATTLE FED A FINISHING RATION Monensin level mg/day 0 50 100 200 300 BARLEY BASED RATION % acetate C2 46.2 45.8 48.8 45.6 44.1 % propionate C3 48.1 48.3 45.5 48.5 51.7 % butyrate C4 5.7 5.9 5.7 5.9 4.2 CORN BASED RATION1 % acetate C2 53.9 50.1 53.9 52.6 % propionate C3 32.3 37.6 33.6 36.8 % butyrate C4 9.1 7.3 7.8 6.6 1 Raun et al, 1974.