It is known that the use of antimicrobials leads to selection of resistant strains and the detection of these isolates in one-day old chickens alert to a possible of vertical resistance in the broiler production pyramid, which potentiates the problem of resistance within the One Health concept, since some antimicrobials used belong to the same class of antimicrobials prescribed in human medicine, such as β-lactams. Thus, monitoring the use of antimicrobials in animal production allows the promotion of rational use of antimicrobials, minimizing the zoonotic risk of transmission of multidrug-resistant bacteria. The aim of this work was to monitor resistance in one-day old chickens, inferring a possible vertical transmission and to evaluate the capacity of horizontal transfer of CTX-M-1 group. The samples were collected in four farms of broiler chicken in northern Paraná, from March 2019 to July 2020. Thirty swabs of one-day-old chickens were collected by a farm before they came into contact with the poultry litter, stored in Cary Blair transport medium and kept refrigerated until processing. Escherichia coli were isolated from the samples, identified by biochemical tests (TSI, SIM, citrate, urea, sorbitol, celobiose), after this, submitted to DNA extraction and PCR research of genes that confer resistance to β-lactams, ESBL research (CTX-M group). Two isolates were evaluated for the horizontal transfer of the CTX-M-1 group by conjugation, for this, two gentamicin sensitive strains belonging to the phylogenetic group B1 were used. As a receptor strain, we used an E. coli isolated from a one-day-old chick, resistant to gentamicin and sensitive to β-lactam strains and belonging to the phylogenetic group D. Were obtained n=120 E. coli, that 55% (66/120) was positive for the CTX-M-1 group, 22% (26/120) for the CTX-M-2 group and 2% (2/120) for the CTX-M-8 group, no positive isolate for the CTX-M-9 group and neither CTX-M-25 group were detected. And when the strains were submitted to the conjugation experiment, they were able to transfer the resistance horizontally, obtaining two transconjugating strains, which presented the CTX-M-1 group. In conclusion, this study demonstrated a high frequency of E. coli CTX-M-1 group on one day old chickens before housing in poultry sheds, indicating the presence of microbiota resistant to important antimicrobials previously the broiler farms and the horizontal transmission capacity of this gene.