Removing Tylosin Phosphate from Finishing Diets with Increasing Roughage Concentrations Affects Growth Performance, Carcass Characteristics, and Prevalence of Liver Abscesses of Finishing Steers

Sunday, September 1, 2024

Liver abscesses are the most common reason for liver condemnation in beef processors.¹ . The average incidence of liver abscesses ranges from 12 to 30% ^{2, 3} but can be as high as 90%.⁴ Liver abscesses in feedlot cattle are a cause of decreased performance and reduced carcass value. Loss in carcass value is due to not only to the abscessed liver being condemned, but also due to trim loss associated with the condemned liver. According to the 2016 National Beef Quality Audit Report,⁵ liver abscesses were the leading cause of offal condemnation (30.8% of livers condemned at slaughter). Brown and Lawrence (2010) estimated that liver abscesses (used 18.1% incidence rate) cost the United States’ cattle feeding industry $15.9 million annually in liver condemnation, trim losses, and reduced carcass weights and quality grades.²

The primary grain used in finishing diets is corn and it is most commonly steam-flaked, and typically constitutes 50% to 90% of dry mater (DM), while 8% to 10% of DM is a typical range for roughage inclusion in finishing diets.⁶ Tylosin phosphate (Tylan, Elanco Animal Health) is an antibiotic that is commonly fed to feedlot cattle to decrease the incidence of liver abscesses. However, general concern that in-feed application of medically important antimicrobials increase antimicrobial resistant pathogen threats to human health remain, so alternative and efficacious means for reducing liver abscesses without antimicrobials are desired. Therefore, a study at a commercial feedyard in the Texas panhandle compared standard finishing diets with or without tylosin phosphate at an industry standard roughage concentration, as well as titrated roughage concentrations in finishing diets containing no tylosin.⁷

In this study, a total of 3,440 steers (primarily of English and English Å~ Continental crossbreeding with average initial weight of 853 lb) were used in a randomized complete block design with 12 pens/treatment and 65 or 70 steers per pen. At the time of initial processing, the steers were randomly assigned to 1 of 4 dietary treatments: (1) standard feedyard finishing diet formulated to contain 7.08% ground corn stalks (DM basis) and 90 mg/steer/day of tylosin (7TYL), (2) finishing diet formulated to contain 7.08% ground corn stalks with no tylosin (NT), (3) finishing diet formulated to contain 13.07% ground corn stalks with no tylosin (13NT), or (4) finishing diet formulated to contain 19.08% ground corn stalks with no tylosin (19NT).

The effect of the treatments on finishing performance are shown in Table 1. Initial body weight (BW) was not different among dietary treatments (P = 0.25). Dry matter intake (DMI) did not differ between the 7% corn stalk roughage treatments (P = 0.74). However, DMI increased linearly with increasing roughage concentration (P < 0.01). Final BW did not differ between the 7% corn stalk treatments (P = 0.58) but was linearly reduced as the roughage concentration increased (P < 0.01). As a result, average daily gain (ADG) was also linearly reduced as the roughage concentration increased (P = 0.01), and gain efficiency (Gain:Feed) worsened linearly as roughage concentration increased (P < 0.01).

The effect of the treatments on carcass characteristics and liver abscesses are shown in Table 2. Hot carcass weight (HCW) and HCW gain were not different between 7% corn stalk treatments but linearly decreased as corn stalk inclusion increased (P < 0.01), such that the 19% corn stalk treatment had 22 lb less HCW compared with the average of the 7% corn stalk treatments (906 vs. 884 lb). Dressing percentage and ribeye area were both reduced in the 7% corn stalk treatment with no tylosin compared with 7% treatment with tylosin (P ≤ 0.04) and linearly decreased as ground corn stalk inclusion increased (P < 0.01).

Tylosin inclusion resulted in a 32% reduction in liver abscess prevalence (from 19.18% to 13.03%, P < 0.01). In addition, the prevalence of liver abscesses was linearly reduced with increased roughage concentration (P < 0.01) such that prevalence of abscesses was reduced by 25% from 19.18% (7% corn stalk treatment with no tylosin) to 14.40% for the 19% corn stalk treatment with no tylosin. These authors suggested that the reduced dressing percentage in the 7% treatment with no tylosin NT compared with the 7% treatment with tylosin could be due to the increased liver abscess prevalence since previous research has shown that liver abscesses cause increased carcass trimming during harvest.3 The reduced dressing percentage in the 19% corn stalk treatment is likely a result of increased gastrointestinal fill. Marbling score did not differ among treatments (P ≥ 0.21) with the exception of a tendency for reduced marbling when the 7% corn stalk treatment with tylosin was compared with the average of 13% and 19% corn treatment with no tylosin (P = 0.07).

Table 1. Finishing performance of steers fed diets containing tylosin or no tylosin with increasing concentrations of ground corn stalks (performance calculated with dead and removed steers excluded).
Item	7TYL	7NT	13NT	19NT	P-value	T	R	L
	Dietary Treatment¹					Contrast²
Pens	12	12	12	12
Days on feed	161	161	161	161
Day 0 BW³, lb	853	853	856	849	0.25	0.91	0.53	0.18
Final BW³, lb	1400^b	1405^b	1400^b	1383^b	<0.01	0.58	0.05	<0.01
ADG, lb	3.40^b	3.42^b	3.37^b	3.29^a	<0.01	0.58	0.05	0.01
DMI, lb	23.57^a	23.64^a	24.48^b	24.89^b	<0.01	0.74	<0.01	<0.01
Gain:Feed	0.144^b	0.145^b	0.138^a	0.133^a	<0.01	0.61	<0.01	<0.01

^a–cMeans within a row with unlike superscripts differ (P < 0.05).

¹Dietary treatments were: 7TYL = 7.08% ground corn stalks with tylosin phosphate (Elanco Animal Health; 90 mg/day) included; 7NT = 7.08% ground corn stalks with no tylosin phosphate included; 13NT = 13.07% ground corn stalks with no tylosin phosphate included; 19NT = 19.08% ground corn stalks with no tylosin phosphate included.

²Probability of orthogonal contrasts: T = 7TYL compared with 7NT; R = 7TYL compared with the average of 13NT and 19NT, and L = linear effect of increasing roughage in the treatments without TYL.

³Initial and final BW were pencil shrunk 4%.

Adapted from Word et al., 2024.

Table 2. Carcass characteristics and liver abscesses of steers fed diets containing tylosin or no tylosin with increasing concentrations of ground corn stalks (performance calculated with dead and removed steers excluded).
Item	7TYL	7NT	13NT	19NT	P-value	T	R	L
	Dietary Treatment¹					Contrast²
Pens	12	12	12	12
HCW, lb	908^b	904^b	900^b	884^a	<0.01	0.52	<0.001	<0.001
Dressing, %	64.78^c	64.43^bc	64.28^b	63.99^a	<0.01	<0.001	<0.001	<0.001
HCW Gain, lb	412^c	410^bc	404^b	392^a	<0.01	0.49	<0.001	<0.001
Ribeye Area, in²	14.48^b	14.29^a	14.24^a	14.24^a	0.04	0.04	0.004	0.64
Fat Thickness, in	0.54^b	0.55^b	0.53^b	0.50^b	<0.01	0.61	0.007	<0.001
Marbling Score	464^b	459^b	461^b	455^b	0.13	0.21	0.07	0.27
Liver Abscessed, %	13.03^a	19.18^b	11.88^a	14.40^a	<0.01	<0.01	0.97	<0.01

^a–cMeans within a row with unlike superscripts differ (P < 0.05).

²Probability of orthogonal contrasts: T = 7TYL compared with 7NT; R = 7TYL compared with the average of 13NT and 19NT, and L = linear effect of increasing roughage in the treatments without TYL.

³Leading digit in marbling indicates score; 4 = small. Subsequent digits indicate degree of marbling within score.

Adapted from Word et al., 2024.

These researchers concluded that “replacing steam-flaked corn with 13% or 19% inclusion of corn stalks in diets without tylosin phosphate could reduce liver abscess prevalence, but increased roughage may not decrease the severity of the liver abscesses”. However, decreased dietary energy density led to increased DMI and reduced HCW in cattle fed to the same days on feed. They also noted that “increasing the roughage concentration in finishing diets introduces production challenges as roughages are typically expensive on a cost per unit of energy basis relative to grain and other concentrates, and therefore limited in finishing diets where minimizing cost per unit of energy is often a goal”. Thus, “this method for reducing liver abscess prevalence would come at the production cost of reduced live growth performance and carcass weight paired with increased feed cost through increased DMI”.

¹ Eastwood, L.C., C.A. Boykin, M.K. Harris, A.N. Arnold, D.S. Hale, C.R. Kerth, D.B. Griffin, J.W. Savell, K.E. Belk, D.R. Woerner, J.D. Hasty, R.J. Delmore Jr., J.N. Martin, T.E. Lawrence, T.J. McEvers, D.L. VanOverbeke, G.G. Mafi, M.M. Pfeiffer, T.B. Schmidt, R.J. Maddock, D.D. Johnson, C.C. Carr, J.M. Scheffler, T.D. Pringle, and A.M. Stelzleni. 2017. National Beef Quality Audit—2016: Transportation, mobility, and harvest-floor assessments of targeted characteristics that affect quality and value of cattle, carcasses, and by-products. Transl. Anim. Sci..1:229–238. Available at: https://doi.org/10.2527/tas2017.0029.

² Brink, D. R., S. R. Lowry, R. A. Stock and J. C. Parrott. 1990. Severity of Liver Abscesses and Efficiency of Feed

Utilization of Feedlot Cattle. J. Anim. Sci. 68: 1201-1207.

³ Brown, T. R. and T. E. Lawrence. 2010. Association of liver abnormalities with carcass grading performance and

value. J. Anim. Sci. 88: 4037-4043.

⁴ Nagaraja, T. G., and K. F. Lechtenberg. 2007. Liver abscesses in feedlot cattle. Vet. Clin. North Am. Food Anim.

Pract. 23:351–369.

⁵ NBQA. 2017. National Beef Quality Audit Executive Summary. Available at:

http://www.bqa.org/Media/BQA/Docs/2016nbqa_es.pdf.

⁶ Samuelson, K. L., M. E. Hubbert, M. L. Galyean, and C. A. Löest. 2016. Nutritional recommendations of feedlot consulting nutritionists: The 2015 New Mexico State and Texas Tech University survey. J. Anim. Sci. 94: 2648-2663.

⁷Word, A. B., K. J. Karr, B. P. Holland, C. L. Maxwell, S. K. Linneen, and P. J. Defoor. 2024. Removing tylosin phosphate from finishing diets with increasing roughage concentrations affects growth performance, carcass characteristics, and prevalence of liver abscesses of finishing steers. Applied Animal Science. 40:260–268. Available at: 10.15232/aas.2023-02489.