Exhibit 99.1 NEWS RELEASE CHARLES RIVER LABORATORIES ANNOUNCES FIRST-QUARTER 2024 RESULTS – First-Quarter Revenue of $1.01 Billion – – First-Quarter GAAP Earnings per Share of $1.30 and Non-GAAP Earnings per Share of $2.27 – – Updates 2024 Guidance – WILMINGTON, MA, May 9, 2024 – Charles River Laboratories International, Inc. (NYSE: CRL) today reported its results for the first quarter of 2024. For the quarter, revenue was $1.01 billion, a decrease of 1.7% from $1.03 billion in the first quarter of 2023. Th ...