Abstract

Antimicrobial resistance (AMR) is a major public health concern, and dairy calves, including veal calves, are known reservoirs of resistant bacteria. To investigate AMR in the fecal microbial communities of veal calves, we conducted metagenomic sequencing of feces collected from individual animals on four commercial veal operations in Pennsylvania. Fecal samples from three randomly selected calves on each farm were collected soon after the calves were brought onto the farms (n = 12), and again, just before the calves from the same cohorts were ready for slaughter (n = 12). Results indicated that the most frequently identified phyla were Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Fecal microbial communities in samples collected from the calves at the early and late stages of production were significantly different at the genus level (analysis of similarities [ANOSIM] on Bray-Curtis distances, R = 0.37, p < 0.05), but not at the phylum level. Variances among microbial communities in the feces of the younger calves were significantly higher than those from the feces of calves at the late stage of production (betadisper F = 8.25, p < 0.05). Additionally, our analyses identified a diverse set of mobile antimicrobial resistance genes (ARGs) in the veal calf feces. The fecal resistomes mostly consisted of ARGs that confer resistance to aminoglycosides, tetracyclines, and macrolide-lincosamide-streptogramin B (MLS), and these ARGs represented more than 70% of the fecal resistomes. Factors that are responsible for selection and persistence of resistant bacteria in the veal calf gut need to be identified to implement novel control points and interrupt detrimental AMR occurrence and shedding.

Highlights

  • There are approximately 9 million dairy cows in the United States, and on average, these animals calve every 13 months (U.S Department of Agriculture [USDA], 2016a; U.S Department of Agriculture [USDA], 2018)

  • Resistant E. coli, including MDR E. coli, were more prevalent in fecal samples taken from veal calves at slaughterage compared with the calves from the same cohorts when they were just brought onto the farms

  • As a follow-up, we sequenced the metagenomes of a subset of the individual fecal samples to characterize the antimicrobial resistance genes (ARGs) in the fecal microbial communities in these veal calves

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Summary

Introduction

There are approximately 9 million dairy cows in the United States, and on average, these animals calve every 13 months (U.S Department of Agriculture [USDA], 2016a; U.S Department of Agriculture [USDA], 2018). Female calves are usually raised as replacement heifers, but male calves are typically sold as bob veal or for dairy beef or veal production. The latter are typically milk-fed and are raised to approximately 16–18 weeks of age or around 450 lbs., and the meat is marketed as. In 2015, close to a half million veal calves were slaughtered under federal inspection in the United States (U.S Department of Agriculture [USDA], and Agricultural Marketing Service [AMS], 2015). Production wastes from livestock, including veal calves, harbor both pathogenic and resistant bacteria, but studies on the microbial communities and their resistomes in veal calf waste are lacking (Um et al, 2016; Salaheen et al, 2019)

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