For males I say never (just my opinion). If you want to I advise for Large breeds 2yrs, Small Breeds 1yr. Same ages for females. Lack of hormones while growing can cause your dog to develop weak and lanky. If you have to do it early, its ok. I'm not a pet dog owner, so I have different standards. Just throwing my opinion in there because I just like to talk dog stuff 
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Because you have 8 females, I'd advise 6 months at the earliest, and make sure they are NEVER left alone together even for a split second. Crate and rotate if you need to.
.Because you have 8 females, I'd advise 6 months at the earliest, and make sure they are NEVER left alone together even for a split second. Crate and rotate if you need to.
