I prefer to spay prior to first heat cycle for many reasons. This is usually at the 6 month mark. Reasons are: after 1st heat chance of mamory gland cancer increases (my senior has this) after second heat it increases drastically, heat cycles are disgusting (blood and the smell!), behavior changes, private areas enlarge after heat cycles (my oldest has this issue), late spayed dogs have increased urinary issues (my oldest has this issue as well).
As for those that spay/neuter at the 2 month-prior to 6th month mark, these are usually rescue dogs from shelters or rescues and they require the dogs to be fixed prior to homing them.
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