how many “deny from” lines are acceptable in a .htaccess

Hello everybody,
I have a system adding automaticaly in my .htaccees deny from IPxxxxxx lines when a visitor makes more than 10 connexions per minute to my website, I’ve done this system because any entry add a line to my database and I want to block any bad crawlers/user/hacker/
the problem is that after 1 year my .htaccess as more than 1000 entry lines, question :
any problem if my .htaccess as a lot of “deny from” lines and at your advice how many lines are acceptable ???
thanks for your response, Luis