An Essential Oil Blend Fed for Growth Performance and Carcass Characteristics to Feedlot Steers

Tuesday, July 1, 2025

Antibiotics are known to reduce mortality, morbidity, and liver abscesses in finishing feedlot cattle (Scott et al., 2017).¹ However, antibiotic resistance concerns have resulted in the reduction/elimination of the sub-therapeutic feeding to livestock to prevent diseases.^{2, 3} Natural additives are actively being studied as stand-alone or in combinations as alternatives to using antibiotics as growth promoters to maintain or improve growth performance Some essential oils (EO) are known for having antimicrobial, antiviral, antifungal, and antioxidant characteristics that may be a feedlot antibiotic alternative to replace monensin sodium (M) and tylosin (T). A unique proprietary EO blend (EOB; Aspire; Ralco Inc., Marshall, MN) consisting of cinnamaldehyde, oregano, and thymol has been developed based upon internal innovative product research and development. Colorado State University researchers conducted a study to evaluate the proprietary EOB fed to finishing feedlot steers for potentially replacing monensin and/or tylosin on growth performance, feed conversions and carcass characteristics.⁴

In this study, 400 crossbred steers (Body Weight [BW] = 813 lb) were blocked by initial BW and cattle source and randomly assigned to 1 of 5 treatments (8 pens/trt; 10 steers/pen) to evaluate an EO blend. Treatments were: 1) Control: no additives added to the steam-flaked corn-based finishing total mixed ration; 2) EOB: proprietary essential oil blend added at 3 g/day plus M and T at 42.4 and 8.5 g/ton, respectively; 4) M + T: M and T added at 42.4 and 8.5 g/ton, respectively; and 5) EOB + M: EOB and M added at 3 g/day and 42.4 g/ton, respectively. Individual BW were measured on two consecutive days at the start and conclusion and every 28 days during the experiment. Equal treatment pen replicates were transported to a commercial abattoir on 160, 174, and 182 days, respectively for collecting carcass data.

The effects of the treatments on feedlot performance are shown in Table 1. Initial, interim 28-day periods, and final BW were similar (P > 0.50) among treatments. However, during the first three 28-day time-periods steers fed EOB along or in combination demonstrated greater average daily gain (ADG) compared with steers fed the remaining treatments. The study remaining time-periods and overall study ADG were similar (P > 0.10) for all treatments. These data demonstrate that feeding EOB improved early feedlot growth rates, but after 84 days there appears to be little benefit to feeding EOB. These researchers speculated that the EOB product characteristics improved feedlot steer performance during receiving and early feedlot phases by reducing stress, diseased challenges, and getting steers on feed.

During the 1^st 28-day time period, dry matter intake (DMI) did not differ between treatments. During the six subsequent 28-day time periods and the overall feeding period, steers on the control diet had greater DMI compared with steers fed M + T (P < 0.05). DMI for steers fed the remaining treatments were intermediate but different (P < 0.05) or similar (P > 0.05). It was speculated that feeding steers an EOB as a flavor in combination with monensin could get receiving steers on feed sooner, thereby reducing stressed and sick or pulls. Overall, study feed efficiency was lowest (P <0.05) for Control steers compared with steers fed the remaining treatments being similar (P> 0.10).

Table 1a. Feedlot finishing performance by steers fed a ration containing a proprietary essential oil blend (EOB), monensin (M), or tylosin (T) alone or in combination.
Item	Treatment Control	Treatment EOB	Treatment EOB+M+T	Treatment M+T	Treatment EOB+M
Pens/treatment	8	8	8	8	8

Table 1b. Feedlot finishing performance by steers fed a ration containing a proprietary essential oil blend (EOB), monensin (M), or tylosin (T) alone or in combination - BW, lb.
Item BW, lb	Treatment Control	Treatment EOB	Treatment EOB+M+T	Treatment M+T	Treatment EOB+M
Initial	811.2	814.1	811.9	811.2	814.5
28 days	906.3	912.4	911.3	908.9	927
56 days	1033.7	1044.3	1028.9	1019.2	1035
84 days	1168.9	1179	1149.9	1140.2	1156.1
112 days	1277.4	1288.4	1266.1	1256.6	1273.8
140 days	1377.2	1390.9	1369.7	1364.7	1376.1
168 days	1467.4	1462.6	1457.3	1438.1	1465.4
Final	1480.4	1485.5	1477.1	1454.9	1481.1

Table 1c. Feedlot finishing performance by steers fed a ration containing a proprietary essential oil blend (EOB), monensin (M), or tylosin (T) alone or in combination - ADG, lb/day.
Item ADG, lb/day	Treatment Control	Treatment EOB	Treatment EOB+M+T	Treatment M+T	Treatment EOB+M
0 - 28 days	3.31^b	3.51^ab	3.55^ab	3.48^ab	4.01^a
29 – 56 days	4.54^a	4.70^a	4.19^ab	3.95^b	3.84^b
57 – 84 days	4.83^ab	4.85^a	4.32^b	4.32^b	4.37^ab
85 – 112 days	3.88	3.95	4.15	4.15	4.21
113 – 140 days	3.57	3.66	3.64	3.86	3.64
140 – 168 days	3.35^a	2.71^b	3.42^a	2.80^b	3.51^a
169 – 181 days	3.79	3.81	3.81	3.7	3.81
Overall	3.9	3.88	3.86	3.77	3.9

^a,b,c Means within the same row with unlike superscripts differ, P < 0.05. Adapted from Poppy et al., 2025. The effects of the treatments on carcass measurements are shown in Table 2. Hot carcass weights

Table 1d. Feedlot finishing performance by steers fed a ration containing a proprietary essential oil blend (EOB), monensin (M), or tylosin (T) alone or in combination - DMI, lb/day.
Item DMI, lb/day	Treatment Control	Treatment EOB	Treatment EOB+M+T	Treatment M+T	Treatment EOB+M
0 - 28 days	16.1	16.1	15.7	15.2	17.2
29 – 56 days	22.9^a	22.3^ab	21.4^bc	20.3^c	20.9^c
57 – 84 days	26.0^a	24.7^b	23.6^bc	22.9^c	22.9^c
85 – 112 days	24.9^a	23.8^b	22.9^b	22.7^b	23.2^b
113 – 140 days	23.8^a	23.6^ab	22.7^b	22.7^b	22.5^b
140 – 168 days	24.5^a	22.9^b	23.8^ab	22.1^b	22.9^b
169 – 181 days	23.4^a	22.5^ab	22.3^b	21.2^bc	21.8^bc
Overall	23.2^a	22.3^b	21.6^bc	20.9^c	21.6^bc

Table 1e. Feedlot finishing performance by steers fed a ration containing a proprietary essential oil blend (EOB), monensin (M), or tylosin (T) alone or in combination - Feed efficiency, BW gain/DMI
Item Feed efficiency, BW gain/DMI	Treatment Control	Treatment EOB	Treatment EOB+M+T	Treatment M+T	Treatment EOB+M
0 - 28 days	0.205^b	0.219^ab	0.229^a	0.230^a	0.234^a
29 – 56 days	0.199	0.212	0.195	0.194	0.185
57 – 84 days	0.185	0.197	0.181	0.189	0.188
85 – 112 days	0.154^b	0.168^ab	0.180^a	0.185^a	0.182^a
113 – 140 days	0.15	0.154	0.16	0.171	0.162
140 – 168 days	0.136	0.112	0.139	0.122	0.149
169 – 181 days	0.163	0.169	0.173	0.76	0.177

The effects of the treatments on carcass measurements are shown in Table 2. Hot carcass weights were similar (P > 0.10) for steers fed all treatments. However, dressing percentages were greater (P <0.05) for steers fed EOB (64.3%) compared with steers fed the remaining treatments (average of 63.15%). The increase in dressing percentage for steers fed EOB resulted in an additional 21.6 lb of marketable carcass based on the calculation of carcass weight times dressing percentages compared to the mean of the remaining 4 treatments. The remaining measured carcass parameters (marbling score, fat thickness, ribeye area, and USDA yield grade) were similar (P > 0.10) for steers fed all treatments. The presence of liver abscesses were lowest (P< 0.05) for steers fed M + T (26.3%) compared with steers fed Control (59.9%), EOB (53.7%), and EOB + M (43.9%) with steers fed EOB+M + T (35.3%) being intermediate and similar (P > 0.10). Several other studies have reported no impact of feeding various EO blends on hot carcass weight, dressing percentage, or other carcass characteristics.5,6,7 These authors noted that future research work is needed to find, if possible, an appropriate blend of specific EO to reduce liver abscesses.

Table 2. Carcass measurements from steers fed a ration containing a proprietary essential oil blend (EOB), monensin (M), or tylosin (T) alone or in combination.
Item	Control	EOB	EOB+M+T	M+T	EOB+M
Hot carcass weight, lb.	901.4	912.4	897.9	883.5	891.9
Dressing percentage¹	63.2^b	64.3^a	63.4^b	63.3^bc	62.7^c
Marbling score²	639.2	601.4	635.2	637.4	634.3
Fat thickness, in.	0.54	0.53	0.49	0.5	0.5
Ribeye area, sq. in.	14	14.1	14.1	13.8	13.7
USDA Yield Grade	2.67	2.71	2.54	2.65	2.54
Liver abscess present, %	59.9^a	53.7^ab	35.3^bc	26.3^c	43.9^abc

¹Final live body weight pencil-shrunk by 4% prior to dressing percentage calculation.

²Slightly Abundant = 800, Moderate = 700, Modest = 600, Small = 500, Slight = 400.
^a,b,cMeans with in the same row with unlike superscripts differ, P < 0.05.

Adapted from Poppy et al., 2025.

These researchers concluded that “feeding finishing steers an essential oil blend improved early feedlot growth rates and dressing percentages with similar feed conversions compared with monensin and tylosin but did not impact incidence of liver abscesses”. This suggest that there is “potential for essential oils to replace sub-therapeutic antibiotic feeding to either enhance (early feedlot) or maintain overall feedlot growth performance and feed conversions”. The feeding of an essential oil blend provides an alternative to feeding antibiotics to feedlot steers. However, the incidence of liver abscess is still a problem to be solved.

¹ Scott, M. F., K. L. Dorton, D. L. Henry, C. R. Belknap, D. L. Hanson, and B. E. Depenbusch. 2017. Effects of feeding a Saccharomyces cerevisiae fermentation prototype on performance, carcass characteristics, and liver abscess prevalence of beef heifers at a commercial feedlot. Prof. Anim. Sci. 33:320–326. Available at: https://doi.org/10.15232/pas.2016-01580

² Salazar, L. F. L., L. A. Nero, M. E. M. Campos-Galvão, C. S. Cortinhas, T. S. Acedo, L. F. M. Tamassia, K. C. Busato, V. C. Morais, P. P. Rotta, A. L. Silva, et al. . 2019. Effect of selected feed additives to improve growth and health of dairy calves. PLoS One. Available at: https://doi.org/10.1371/journal.pone.0216066.

³ Cangiano, L. R., T. T. Yohe, M. A. Steele, and D. L. Renaud. 2020. Invited review: strategic use of microbialbased probiotics and prebiotics in dairy calf rearing. Appl. Anim. Sci. 36:630–651. Available at: https://doi.org/10.15232/aas.2020-02049.

⁴ Poppy, C., M. N. Nair, L. N. Edwards-Callaway, K. Stackhouse-Lawson, J. N. Martin, C. V. Scharlau, H. L. Doering-Resch, D. P. Casper, and T. E. Engle. 2025. An essential oil blend fed for growth performance and carcass characteristics to feedlot steers. Transl. Anim. Sc. Available at: https://doi.org/10.1093/tas/txaf065.

⁵ Meyer, N. F., G. E. Erickson, T. J. Klopfenstein, M. A. Greenquist, M. K. Luebbe, P. Williams, and M. A. Enstrom. 2009. Effect of essential oils, tylosin, and monensin on finishing steer performance, carcass characteristics, liver abscesses, ruminal fermentation, and digestibility. J. Anim. Sci. 87:2346–2354. Available at: https://doi.org/10.2527/jas.2008-1493.

⁶ Araujo, R. C., D. R. Daley, S. R. Goodall, S. Jalali, O. A. Guimaraes Bisneto, A. B. Budde, J. J. Wagner, and T. E. Engle. 2019. Effects of a microencapsulated blend of essential oils supplemented along or in combination with monensin on performance and carcass characteristics of growing and finishing beef steers. Appl. Anim. Sci. 35:177–184. Available at: https://doi.org/10.15232/aas.2018-01822.

⁷ Pukrop, J. R., B. T. Campbell, and J. P. Schoonmaker. 2019. Effect of essential oils on performance, liver abscesses, carcass characteristics and meat quality in feedlot steers. Anim. Feed Sci. Technol. 257:114296. Available at: https://doi.org/10.1016/j.anifeedsci.2019.114296.

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An Essential Oil Blend Fed for Growth Performance and Carcass Characteristics to Feedlot Steers