Effect of monensin withdrawal on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus taurus steers consuming bermudagrass hay

Authors: BELL, NATASHA - TEXAS A&M UNIVERSITY; CALLAWAY, TODD; Anderson, Robin; FRANCO, MARCIA - UNIVERSIDADE FEDERAL DE VICOSA; SAWYER, JASON - TEXAS A&M UNIVERSITY; WICKERSHAM, TYRON - TEXAS A&M UNIVERSITY

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2017
Publication Date: 6/8/2017
Publication URL: https://handle.nal.usda.gov/10113/6472221
Citation: Bell, N.L., Callaway, T.R., Anderson, R.C., Franco, M.O., Sawyer, J.E., Wickersham, T.A. 2017. Effect of monensin withdrawal on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus taurus steers consuming bermudagrass hay. Journal of Animal Science. 95(6):2747-2757. https://doi.org/10.2527/jas.2016.1013.
DOI: https://doi.org/10.2527/jas.2016.1013

Interpretive Summary: Monensin is an antibiotic commonly used as a feed additive in the beef industry, more so with cattle fed diets containing high amounts of grains but becoming more common with cattle fed diets containing large amounts of hay. Monensin is thought to improve the animal's ability to digest the food it eats, particularly for the protein part of the diet, which is often lacking for cattle fed hay. While monensin use is increasing with cattle fed hay, little is known what happens when monensin feeding ceases. Consequently, this study was conducted to evaluate the effect of monensin withdrawal in hay-fed cattle. We found that withdrawal of monensin resulted in a change in some of the digestion end products in these hay-fed cattle, with a preferred high energy end product, called propionate, being produced at a lower amount after withdrawal than before withdrawal, but the amount produced still appeared to be higher than in cattle that had not received monensin at any time. Moreover, the decrease in the amount of the preferred end product propionate during withdrawal from monensin appeared to be compensated by the production of higher amounts of other end products. It has been shown in other studies that monensin decreases the amount of methane produced by cattle and we found in the present study that while rates of methane production did not increase upon monensin withdrawal to a level that would be statistically significant, it did appear that methane production was becoming more like that observed in cattle having not been fed monensin. We further found the effects of monensin withdrawal was similar whether we used Brahman type cattle, commonly raised in the hot southwest regions of the United States, or cattle of European descent which are typically more common in other regions of the country, although this latter type of cattle appeared to be better suited to the type of hay we used. Overall, these results indicate that there were little if any negative effects of monensin withdrawal over the period time of our study. Ultimately, this information will help farmers and ranchers best use the tools at their disposal to raise their cattle as efficiently as possible for continued production of wholesome meat and milk for the American consumer.

Technical Abstract: Effects of monensin withdrawal and cattle subspecies on the utilization of bermudagrass hay (14.3% CP, 72.3% NDF, and 36.9% ADF) were evaluated using ruminally cannulated steers (5 Bos Taurus indicus [BI] and 5 Bos taurus taurus [BT]). Subspecies were concurrently subjected to a 2-period, 2-treatment crossover design. Treatments consisted of either 0 mg·steer**-1·d**-1 monensin with no previous monensin feeding (CON) or withdrawal from 200 mg·steer**-1·d**-1 monensin (MON) fed individually in 0.91 kg dried distillers' grains with solubles for 42 d. Withdrawal was evaluated for a 28-d period. Ruminal fluid was collected 2 h after feeding on d 0, 1, 4, 7, 14, and 21 after withdrawal for determination of pH, VFA, ruminal NH3-N (RAN), rate of NH3 production, and CH4 production rate. Hay, ort, and fecal grab samples were collected d 23 through 28 after withdrawal for determination of intake and digestion. No subspecies x monensin, subspecies x day, or subspecies x monensin x day interactions were observed (P greater than or equal to 0.11). An effect of day after monensin withdrawal was observed (P < 0.01) for total VFA concentration, with an increase following withdrawal followed by a decrease and then stabilization. Monensin x day after monensin withdrawal interactions (P less than or equal to 0.01) were observed for the acetate:propionate (A:P) ratio and molar percent of acetate and propionate. There was a decrease in molar percent of propionate between d 1 and 4 from 19.1 to 18.0; however, it remained greater (P less than or equal to 0.10) for MON than CON through d 7. Withdrawal increased molar percent of acetate from 68.3 to 69.8 between d 0 and 4 for MON steers. The A:P ratio was less (P less than or equal to 0.01) on d 0 for MON than for CON (3.4 vs. 4.0), but by d 4, it increased to 3.8 and was not different (P = 0.14) from CON. By d 14, no differences (P greater than or equal to 0.88) remained for acetate, propionate, or the A:P ratio. After monensin withdrawal, monensin reduced (P < 0.01) RAN by 12.3% (2.09 vs. 1.83 rnM for CON and MON, respectively). Monensin withdrawal and cattle subspecies had no effect (P greater than or equal to 0.23) on rate of NH3 production or CH4 production rate. Monensin withdrawal had no effect (P greater than or equal to 0.45) on intake or digestibility parameters. Greater forage OM intake (P = 0.09; 21.2 vs. 19.2 g/kg BW) and OM digestibility (P < 0.01; 72.4 vs. 63.0%) resulted in greater (P < 0.01) total digestible OM intake (16.8 vs. 13.2 g/kg BW) in BT steers than in BI steers. These results suggest that BT steers are better able to utilize bermudagrass hay than BI steers. Upon monensin withdrawal, steers previously fed monensin continue to have a reduced A:P ratio for at least 7 d.