DECLARE latest_exam date;

  SELECT DATE(MAX(ex_date))
    INTO latest_exam
    FROM vets
   WHERE an_id = p_animal_id
GROUP BY an_id;

SELECT latest_exam, and a bunch of other stuff. ;

SELECT x.maxDate,
       b.*
FROM tableName b,
    (
        SELECT DATE (max(ex_date)) maxDate
        FROM vets
        WHERE an_id = p_animal_id
        GROUP BY an_id
    ) x

select latest_exam = date(max(ex_date))..