Effects of intermittent feeding of tylosin phosphate during the finishing period on feedlot performance, carcass characteristics, antimicrobial resistance, and incidence and severity of liver abscesses in steers1

Abstract

Liver abscesses (LA) are a source of economic loss for feedlot cattle feedlots, and the 2017 veterinary feed directive has restricted further use of tylosin phosphate to prevention and control of LA. Our objective was to evaluate effects of intermittent tylosin phosphate feeding on incidence and severity of LA in feedlot cattle and presence of total antimicrobial-resistant Enterococcus spp. Steers (n = 312, 411.4 ± 6.71 kg) were blocked by initial BW and randomly assigned to a treatment group. Treatments included a negative control group (no tylosin phosphate throughout the finishing period), a positive control group (tylosin phosphate fed continuously throughout the finishing period), and a group that received tylosin phosphate off-label by feeding the drug on a repeated intermittent basis (1 wk on, 2 wk off). Steers were housed in 24 soil-surfaced pens with 13 steers per pen. Body weights of cattle were obtained every 28 d and at the end of 119 d the steers were weighed and harvested at a commercial abattoir. Fecal samples were collected on days 0, 21, and 118 to characterize antimicrobial-resistant Enterococcus spp. Total LA percentage was greater (P = 0.012) for the no tylosin phosphate treatment compared with the other treatments, but did not differ between the continuous tylosin phosphate treatment and the intermittently fed tylosin phosphate treatment (P = 0.716). No difference was observed among treatments for ADG (P = 0.21), DMI (P = 0.28), or G:F (P = 0.75). Marbling score was lower (P = 0.022) for tylosin phosphate treatment when compared with both intermittent treatment and continuous tylosin phosphate treatment. Enterococcus spp. bacterial counts did not differ by treatment group over time (P > 0.05); however, there was a strong period effect for macrolide resistance among all groups (P < 0.01), suggesting an important environmental component as cattle were first placed in pens and then progressed through the feeding period. We conclude that feeding tylosin phosphate intermittently during the finishing phase decreases the total percentage of LA and maintains feedlot performance and carcass characteristics to the same extent as feeding tylosin phosphate throughout the finishing phase; furthermore, we hypothesize that enteric antimicrobial resistance is a result of longer term antibiotic usage in a particular environment rather than a direct short-term result of the treatment during any given feeding period.

Macrolide‐susceptible probioticEnterococcus faeciumST296 exhibits faecal‐environmental‐oral microbial community cycling among beef cattle in feedlots

“…Beukers et al () suggested that early withdrawal of tylosin prior to slaughter contributed to a lower proportion of macrolide‐resistant enterococci. Additionally, Müller et al () noted that the environment where cattle are raised, namely where antibiotics have previously been used, seemed to play a large role in the presence of macrolide‐resistant enterococci. Interestingly E. faecium is also worthy of investigation as a probiotic, due to its tolerance of bile acids and its antagonistic effects towards intestinal pathogens; specifically, it harbours bacteriocins active against Gram‐positive foodborne pathogens, such as Listeria monocytogenes (Izquierdo et al ) .…”

Investigation of a Reduction in Tylosin on the Prevalence of Liver Abscesses and Antimicrobial Resistance in Enterococci in Feedlot Cattle

“…They observed a reduction in macrolide resistance, just prior to and after the removal of tylosin. Müller et al (17) explored the intermittent use (1 week on, 2 weeks off) of tylosin compared to continuous or no tylosin and found no difference in Ery R enterococci between tylosin treatment at each time point. However, these researchers did record a higher percentage of Ery R enterococci with increasing days on feed between day 20 and day 118.…”

“…It has been proposed that the administration of tylosin may coselect for enterococci with resistance to tetracycline, even in the absence of tetracycline use (45). Müller et al (17) reported increased proportion of Tet R enterococci in cattle feces with increasing days on feed, but found no relationship between Tet R occurrence and the administration of tylosin in feed. Although tetracycline was absent in the diet, Müller et al (17) observed an initially high proportion of Tet R enterococci in cattle feces at approximately 10% on day 0, with increases between day 20 (∼20%) and day 118 (∼40%).…”

“…Another feedlot study in the United States investigated the impact of intermittent (1 week on, 2 weeks off) and continuous administration vs. no tylosin on erythromycin resistance (Ery R ) in enterococci. They found no difference in the occurrence of liver abscesses between intermittent and continuous treatments, but there were more liver abscesses in cattle that did not receive tylosin (17). As such, it is important to continue to investigate ways to optimize tylosin use while promoting antimicrobial stewardship, supporting productivity, and working to minimize use of antimicrobials in livestock that are of importance in human medicine.…”

Critically important antibiotics: criteria and approaches for measuring and reducing their use in food animal agriculture

“…Other FDA requirements pertaining to how antibiotics must be administered may actually drive up drug use in practice. For example, a recent study found that intermittent feeding of tylosin achieves reduction of liver abscesses in cattle comparable to continuous feeding, but this strategic antibiotic use may violate laws governing specific use practices . Given the regulations on antibiotic use, veterinarians may be required to administer higher doses than they feel is necessary, or for longer than needed, to prevent disease…”