Effects of Intermittent Feeding of Tylosin Phosphate on Feedlot Performance, Carcass Characteristics, and Incidence of Liver Abscesses in Steers

Liver abscesses (LA) are a source of economic loss in feedlot cattle, and tylosin phosphate historically has been fed to decrease LA incidence and severity. This study was conducted to evaluate intermittent feeding of tylosin phosphate as strategy to decrease usage of a medically important antibiotic, and to study impact on cattle performance and incidence of liver abscesses. Steers (n = 312; 411 ± 6.7 kg initial BW) were blocked by weight and randomly assigned, within block, to one of 3 treatments in a randomized complete block experiment. Treatments included no tylosin (NC), tylosin fed continuously (CT) at 10 g/T diet DM, and tylosin fed on an intermittent basis (IT; 1 wk on, 2 wk off). Steers were housed in 24 dirt-surfaced pens with 13 steers/pen and fed once daily ad libitum. Finishing diets contained 57.7% steam-flaked corn, 30% wet corn gluten feed, 8% corn silage and 2.3% supplement (DM basis), and supplied 33 g/T monensin and either 0 or 10 g/T tylosin. At the start of the trial steers were weighed, vaccinated against clostridial and viral pathogens, treated with a topical parasiticide, and implanted with estradiol-trenbolone acetate implants. Steers were harvested after 119 d. No differences were observed among treatments for ADG, DMI, or feed efficiency (P > 0.20). Marbling score was lower for CT compared to IT and NC (Sm²⁹, Sm⁵⁸, and Sm⁵⁵, respectively; P = 0.022), but no other differences were observed for carcass traits (P > 0.10). Incidence of LA was greater for NC compared to IT and CT treatments (P = 0.012), but IT and CT were not different (P >0.50). Intermittent feeding of tylosin decreases overall use of antibiotics in feedlot cattle without compromising cattle performance or incidence of liver abscesses.

	Treatment
Item	No Tylosin	Continuous Tylosin	Intermittent Tylosin	SEM	P- value
ADG, kg	1.82	1.86	1.79	0.037	0.207
DMI, kg/d	10.88	11.20	10.85	0.236	0.278
Gain:feed	0.1673	0.1661	0.1650	0.0027	0.752
HCW, kg	380.3	383.1	380.3	7.58	0.512
USDA Choice + Prime, %	76.0	73.4	78.7	5.88	0.671
Total LA, %	21.4	7.8	9.6	4.65	0.012