Effect of monensin inclusion 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; Anderson, Robin; Callaway, Todd; FRANCO, MARCIA - Universidade Federal De Viçosa; SAWYER, JASON - Texas A&M University; WICKERSHAM, TRYON - Texas A&M University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2017
Publication Date: 6/8/2017
Publication URL: http://handle.nal.usda.gov/10113/5863783
Citation: Bell, N.L., Anderson, R.C., Callaway, T.R., Franco, M.O., Sawyer, J.E., Wickersham, T.A. 2017. Effect of monensin inclusion 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):2736-2746. https://doi.org/10.2527/jas.2016.1011.
DOI: https://doi.org/10.2527/jas.2016.1011

Interpretive Summary: Monensin is an antibiotic widely used as a feed additive in beef feedlots where cattle are fed diets containing high amounts of grain. While monensin has traditionally been added in small quantities to cattle feed containing high amounts of hay, there is an increasing interest to do so. For instance, monensin is thought to improve the animal’s digestive efficiency, particularly for protein, which is often lacking for cattle being fed hay. Consequently, the objective of this study was to evaluate the effect of supplementing a hay-based diet with monensin on cattle performance. Cattle fed hay diets with or without monensin supplementation ate the same amount of hay. However, during digestion, the cattle that ate the monensin-supplemented hay converted the hay to more energy efficient end-products that would be better used by the animal than the cattle that ate hay that was not supplemented with monensin. Additionally, cattle that ate the monensin-supplemented hay produced less methane than the cattle fed hay that was not supplemented with monensin. These results indicate that feeding monensin to cattle fed hay may help them produce more meat and milk while contributing lower amounts of the greenhouse gas and methane to the atmosphere. Ultimately, these results will help farmers and ranchers produce more wholesome meat and milk at lower cost and with a lower environmental impact for the American consumer.

Technical Abstract: Effects of monensin inclusion and cattle subspecies on utilization of bermudagrass hay (13.7% CP, 77.3% NDF, and 38.8% ADF) were evaluated using ruminally cannulated steers (5 Bos taurus indicus [BI] and 5 Bos taurus taurus [BT]; 398 kg BW). Subspecies were concurrently subjected to a 2-period, 2-treatment crossover design. Treatments were 0 (CON) or 200 mg·steer**-1·d**-1 monensin (MON) in 0.91 kg dried distillers’ grains with solubles. Periods were 70 d in length: 20 d of adaptation, 22 d of sample collection, and 28 d for withdrawal of treatment. Steers were group housed during adaptation and moved to individual covered pens for sampling. Hay, ort, and fecal grab samples were collected d 21 through 25 for determination of intake and digestion. Ruminal fluid was collected with a suction strainer 0, 2, 4, 8, and 12 h after feeding on d 42 for pH, VFA, and ruminal NH3–N (RAN) analysis. Additionally, at h 2, ruminal fluid and contents were collected for determination of rate of NH3 production and CH4 production rate. No subspecies × monensin interactions were observed (P greater than or equal to 0.12). Monensin had no effect (P greater than or equal to 0.16) on intake or digestibility parameters. No subspecies effect (P greater than or equal to 0.11) was observed for forage OM intake, total OM intake, or OM digestion. Total digestible OM intake tended to be greater (P = 0.06) for BT steers than for BI steers (14.0 vs. 12.2 g/kg BW). There was an effect of hour after feeding (P less than or equal to 0.01) on pH, total VFA, acetate:propionate ratio, and molar percent acetate and propionate. Total VFA concentration was greater (P = 0.01) in CON steers than in MON steers (66.5 vs. 62.0 mM). Monensin decreased molar percent acetate (P = 0.02) from 72.5 to 71.2% and increased molar percent propionate (P < 0.01) from 16.9 to 18.7%, resulting in a reduced (P < 0.01) acetate:propionate ratio (from 4.34 to 3.85). Although not significantly (P = 0.19), monensin numerically reduced the CH4 production rate by 15.8%. Greater (P = 0.07) CH4 production rate tended to be observed in BI steers than in BT steers (21.4 vs. 16.6 µmol CH4·mL**-1·h**-1, respectively). Monensin had no effect (P greater than or equal to 0.32) on pH, RAN, or rate of NH3 production. A subspecies × hour after feeding interaction was observed for RAN, with BT having greater RAN at h 0 and 4, whereas BI had greater RAN at h 2, 8, and 12. Overall, monensin decreased the acetate:propionate ratio and total VFA concentration but had no effect on forage utilization. Bos taurus indicus steers consumed less digestible OM and had a greater CH4 production rate compared with BT steers, suggesting BT were better able to utilize the available forage resource than BI.