Silky Terrier and Yorkie dont get along

Question
I have a 9 month old silky terrier male and my girlfriend has a 5 month old yorkie female. Whenever they are separate they are both fine, affectionate and calm. But when the 2 are together they both nip, wrestle, growl and  chase each other for hours. My silky will extremely often, try to put his snout under her bottom. He'll slide on his back or continue to follow behind her and sniff and /or lick from behind.And thats usually when the female yorkie gets angry.He is neutered but she is not fixed, is this the reason for the constant rough play and sniffing?

Answer
Hello Micah, It could be, however this behavior is also a demonstration of dominance.  And some of it is just play and to be expected.  I would get her fixed as soon as possible.  Also keep in mind if you recently got your Silky fixed it still takes a few months for the hormones to completely settle down.  Good luck, and Thanks for asking, Cindy Lou :)