Extension

Liver abscesses are a source of economic loss in the feedlot cattle industry, with an estimated annual impact of over $60 million in visceral losses alone.¹ Severe abscesses often extend into adjacent organs and tissues, requiring excision of the liver and trimming of the carcass during slaughter, thus decreasing carcass weight and overall carcass value compared with cattle without liver abscesses.² Furthermore, cattle with severe abscesses also have reduced feedlot performance compared with cattle that are abscess free, because of decreased intakes, daily gains poorer feed efficiency.³

 

Tylosin phosphate (Tylan 100; Elanco Animal Health, Greenfield, IN) is an antibiotic that has been commonly fed to feedlot cattle for decades to prevent liver abscesses in feedlot cattle. The approved use by the US Food and Drug Administration Center for Veterinary Medicine is for continuous feeding throughout the finishing phase at 8.8 to 11 grams/ton of tylosin phosphate (90% DM basis) to provide 60 to 90 mg/animal/day. Since tylosin is a macrolide and macrolides are categorized as medically important antibiotics with wide human therapeutic applications, the feedlot industry is seeking ways to reduce the use of tylosin. Recent Kansas State University research evaluated the effects of the lower end of the approved dose range, 60 mg/steer/day of tylosin phosphate administered during the initial 30 or 60 days of the finishing phase on the incidence and severity of liver abscesses, cattle growth performance, and carcass characteristics.⁴

 

In this study, 462 crossbred steers (initial weight = 831 lb) were randomly assigned to 1 of 3 treatments: no tylosin phosphate (control) or tylosin phosphate, administered in the feed to provide 60 mg/steer/day the first 30 days (T-30) or 60 days (T-60) of the finishing phase. Steers were fed the control diet for the remaining days of the finishing phase. The steers were housed in pens with 7 steers per pen and 22 pens per treatment. Cattle body weights (BW) were recorded at 30-day intervals, and final BW was recorded on day 161 on feed. The steers were processed at a commercial abattoir, and incidence and severity of liver abscesses and carcass characteristics were recorded.

 

The effects of treatment on the incidence of liver abscesses and severity of liver abscesses are shown in Table 1. Tylosin phosphate administered strategically in the first 30 or 60 days of the finishing period did not affect total liver abscess incidence (P = 0.93). Abscesses categorized as A− or A (mild abscesses) also did not differ among the treatments (P > 0.10). However, cattle fed tylosin phosphate for the first 30 or 60 days tended to have fewer severely (A+) abscessed livers (P = 0.10) compared with the control, fed no tylosin phosphate. These researchers attributed this effect to the use of tylosin phosphate during the diet adaptation phase (first 21 days) when cattle are likely to experience ruminal acidosis.

 

No differences in steer performance were observed between treatments over the entire feeding period. However, it was observed that on day 30, steers that received tylosin phosphate had greater BW compared with steers on the control treatment (P < 0.01), but feed intake was unaffected (P > 0.14). By day 60 (30 days after withdrawal of tylosin from T-30), measures of cattle growth performance (BW, ADG, DMI, and G:F) were not different between the control and T-30 (P = 0.14, P > 0.14, P > 0.14, and P > 0.14, respectively). In contrast, cattle in the T-60 treatment had greater BW on day 60 (P = 0.04) compared with the control or T-30, but ADG, DMI, and G:F did not differ among treatments (P > 0.14). No differences in cattle performance were noted among the three treatments during the remainder of the finishing phase (P > 0.05). Steer carcass characteristics were not affected by treatments.

 

¹The control treatment did not receive tylosin phosphate throughout the feeding period; T-30 received 60 mg/steer/day for the first 30 days and on day 31 was transitioned to the control diet; and T-60 received 60 mg/steer/day for the first 60 days and on day 61 was transitioned to the control diet.

 

²Liver abscess scores were assessed as 0 = no abscesses; A− = 1 or 2 small abscesses; A = 2 to 4 abscesses less than 2.54 cm in diameter; and A+ = 1 or more large abscesses or multiple small- or medium-sized abscesses with or without adhesions. ³P < 0.10. Adapted from Fietoza et al., 2025.

 

These researchers concluded that “strategically feeding tylosin phosphate at a targeted dose of 60 mg/steer/day, which is the lower end of the approved dose range, during the first 30 or 60 days of the finishing period did not affect liver abscess incidence, but there was a trend for reduced incidence of A+ abscesses”. They noted that “a major limitation of the targeted duration of tylosin administration is lack of evidence for the timing of abscess development because of the inability to detect liver abscesses in live cattle”. “An evidence-based timing of liver abscess development needs to be determined before designing studies that focus on strategic duration of tylosin phosphate administration to reduce the overall use of medically important antibiotic in feedlot cattle.”

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¹ Herrick, R. T., C. L. Rogers, T. J. McEvers, R. G. Amachawadi, T. G. Nagaraja, C. L. Maxwell, J. B. Reinbold, and T. E. Lawrence. 2022. Exploratory observational quantification of liver abscess incidence, specific to region and cattle type, and their associations to viscera value and bacterial flora. Appl. Anim. Sci. 38:170–182. Available at: https://doi.org/10.15232/aas.2021-02228

 

² Grimes, B. B., T. J. McEvers, T. C. Tennant, J. W. Johnson, and T. E. Lawrence. 2024. Relationship of liver abnormalities with carcass performance and value. Appl. Anim. Sci. 40:358–375. Available at: https://doi.org/10.15232/aas.2023-02482.

 

³ Batista, L. F., and B. P. Holland. 2022. Liver abnormalities in cattle: Effect of liver abscessation on growth and productivity of cattle. Vet. Clin. North Am. Food Anim. Pract. 38:347–360. Available at: https://doi.org/10.1016/j.cvfa.2022.08.002.

 

⁴ Feitoza, L. F. B. B., A. N. Baker, R. L. Thorn, L. S. Monteiro, F. Nasiu, T. G. Nagaraja, Q. Kang, and J. S. Drouillard. 2025. Targeted durations of tylosin phosphate on incidence and severity of liver abscesses in feedlot cattle. Appl. Anim. Sci. 41:1-9. Available at: https://doi.org/10.15232/aas.2024-02574.