Charles River Laboratories International (CRL) 10-Q2024 Q3 Quarterly report

Exhibit 32.1

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the quarterly report on Form 10-Q for the quarter ended September 28, 2024 of Charles River Laboratories International, Inc. (the “Company”) as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, James C. Foster, Chairman, President and Chief Executive Officer of the Company, and Flavia H. Pease, Corporate Executive Vice President and Chief Financial Officer of the Company, each hereby certifies, to the best of his knowledge and pursuant to 18 U.S.C. Section 1350, that:

(1)    the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (the “Exchange Act”); and

(2)    the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.