Q. Our female dog is currently in heat and our unaltered male Labrador Retriever has been more interested in our unaltered male Chihuahua then in her! We are planning to get both our female and our male Lab spayed and neutered but until then, we are wondering why our dog has suddenly switched sides. Hope you can shed some light on this!
A. It might seem quirky, but it's quite normal for intact male dogs, especially young, inexperienced ones, to do this kind of thing when a female dog is in season. The female's season lasts for several weeks, but during that time there are only a few days when she'll allow a male to breed with her. Her scent during the whole period will excite any nearby males, sometimes even neutered males, and they'll try to court the female. If she's not ready to be interested in their advances yet, she'll rebuff them with a snarl or a nip. Males will then try to work off their hormonal urges by “playing” the mating dance with another dog, even another male if that's all who's available.
After you get your female spayed and your Lab neutered, this hormone-frenzy won't happen any more. It's possible, though, that your Lab might continue to try and mount your Chihuahua, either in play or as a bossy gesture. If that behavior doesn't seem to upset your Chi, you can stay out of it and they'll work out their own relationship. If the Lab persists after the Chi tells him to quit, give the little guy some support by calmly intervening. Put the dogs in their crates or in separate rooms for about 20 minutes, until they both calm down. Then you can let them be together again, with you monitoring for 10 minutes or so, to be sure the Lab won't start picking on the Chi again.