What is the normal age for a chihuahua to go into heat?

Most female dogs go into heat about every 6 months. You should not have any problem with your male dogs behavior since he is fixed.
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Your pup will probably go into heat around 6 months old. Just make an appointment to have her spayed at that age and you won't have to worry about how your Lab will act.
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I have known of Chi's going into heat anytime after 5 months. 6-8 months is most common. I am having my 5 month old Chi spayed tomorrow so as this won't be an issue.

Your male will not bother her if she goes into heat, but it's best all around for her if you have her spayed before her first heat. 5-6 months to have this done would be just perfect for her.
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Owner of 4 Chihuahua's

6 months to 1 yr . Your Lab won't care if she is in heat he may smell and lick but that will be about it.The heat cycle last 21 days 7 going in 7 which they can be breed and 7 doing out of heat if you don't plan on breeding her then have her spayed it will be more healthier for her.
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Dogs can go through estrus (heat) between every 4 - 8 months. At 9 weeks, she shouldn't be old enough yet but they can still have a vaginal discharge at this time. it's usually normal. Your male should be fine as long as he is properly trained and hopefully you will be spaying your puppy soon. If there is a problem you're specifically concerned about, consult your veterinarian on the next puppy vaccine visit.
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The male will probably sniff her a lot since she'll be producing a new odor, but he will not try to mate with her. She will be more irritable during her heat cycle and they may get in fights because of that.

You really should have her spayed as soon as she's old enough though. It's healthier for her and you won't have to worry about behavioral changes during her heat, the blood dripping, or the responsibility of puppies.

I had both my chi's (a male and a female) spayed and neutered at 5.5 months old. It's such a load off to know I don't have to worry.
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Females usually go into heat around 8-12 months of age. If you get her fixed at 6 months you won't have this problem. Heats are messy and gross and last for 21 days, in the meantime she cannot be allowed outside without a leash, must be monitored at all times and you cannot take your eyes off of her for one second outside, it will take 1 second for an unfixed male to smell her and get at her. If your male lab is fixed he might attempt to hump her, although it will be impossible to do. I had a male fixed foster dog that kept trying to hump this female at the dog park, I asked the owners if she was fixed they said yes so I didn't worry about it, however, turns out she wasn't fixed she was in heat and even though the foster was fixed he still kept trying to hump her. So I am not going to say your fixed lab won't try something.

Take the worry out of this and get her spayed.
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