Male dog chasing recently fixed female???

I recently had my female dog spayed (A day or so ago) but from the moment I brought her home, (since I brought her through the door) my unfixed male dog has been acting as though she's in heat. Popping his jaws at her, trying to sniff at her or spots she's been laying, attempting to bait her with food or play. He even attempted to mount her to no avail. (I was standing right there) I've been keeping them separated in different rooms, but it doesn't deter him. We have one smaller unfixed male as well, but he's showing no interest in her at all. I don't understand why my male is acting like this. 

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