Sexual maturity in dogs is breed and size dependent; for most puppies, it will occur between 6-9 months of age, though it may be slightly earlier for a small breed dog and a bit later if you own a large breed puppy like a Great Dane or Saint Bernard. Thus, the average female dog will have their first estrous cycle (i.e. go into heat) somewhere between 6-9 months. There are four stages to the estrous cycle in dogs and they can only get pregnant during one of those stages. These stages are characterized by different behaviors that you will want to watch for:
Proestrus: This stage lasts about 9 days, but can go as long as 27 days. Male dogs are attracted to female dogs in proestrus but the females will spur their advances. Dog owners will often notice that their female dog's vulva is swollen and they will begin to notice a red discharge which can last 7-10 days, beginning as sort of a thin, watery, pale red consistency, to a thicker, darker red in color. Female dogs will lick themselves more and they tend to urinate more as well. This increased frequency of urination serves a purpose; the urine is filled with wonderful, pheromonal and hormonal smells designed to attract potential suitors!
Estrus: This is the stage when female dogs will show active interest in male suitors, typically lasting 9 days, but can go as long as 24 days. This is when your female dog is fertile! You will notice less discharge at this stage. This is the stage during which your female dog can get pregnant!
Diestrus: This is the stage where your female dog is back to ignoring the advances of male dogs around her and lasts for about 2 months.
Anestrus: This stage lasts about 4 months and is basically the time period between diestrus and the start of your dog's next heat cycle/proestrus. Your dog's vulva should no longer be swollen and there shouldn't be any discharge. If your dog is pregnant, however, pregnancy lasts about 9 weeks.
I've had puppy owners tell me that they've read that female pups cannot get pregnant during their first heat cycle, that pregnancy won't occur unless the dogs "tie," and that brother/sister matings are unlikely to occur AND that they won't result in pregnancy if they do happen. All of these statements are false; female dogs can indeed get pregnant during their first cycle, dogs don't have to remain tied together for the female to get pregnant, and siblings will mate and reproduce if allowed to do so.
Let's talk about male dogs for a minute. Male dogs are capable of reproducing year-round. They are sexually mature sometime after 5 months of age, though they are most fertile after a year of age. Adolescent male dogs have the highest testosterone levels which is likely why young male dogs are targeted for aggression at the dog park and other places where unfamiliar dogs gather. Marking their territories (potentially both inside and outside your house!) will start occurring, as will roaming if you don't keep your intact male dog adequately supervised. If you notice your young male dog doing a lot of sniffing, licking of urine, and marking around a particular house in your neighborhood, it is likely there is an intact female dog nearby in estrus and he's claiming that turf!
So, let's circle back to puppy class. If you are attending a puppy class and all of the puppies are under 5 months of age, that mounting behavior you see happening during class isn't about sex/reproduction, but about play. If you are attending an older puppies/adolescent dogs class (that is, a class where dogs are over 6 months of age), AND the dogs are off leash, THEN you will want to watch the behavior of the interacting dogs more closely. You will see male dogs sticking their noses into the vulvas of the female dogs in the class (basically checking to see where they are in the estrus cycle) and you will definitely see female dogs politely sitting down to avoid this and/or whipping around and snapping at the offensive male dog. You should not, however, attend classes if you notice that your female dogs has started going into heat as evidenced by that enlarged vulva, licking behavior, etc. And it goes without saying that female dogs in heat should not be taken to the dog park; even walking a female dog in heat out in public can create pandemonium. Best to walk female dogs in heat at off peak times and off peak places, or limit their exercise to your home and yard to keep them safe from an unwanted pregnancy.
I recently had a client tell me that this was all so much easier when everyone spayed or neutered their puppies between 4-6 months of age. While that may be true from a convenience point of view for us, their caretakers, the bottom line is that delaying spaying/neutering will result in healthier dogs, better protected from cancers and with appropriate brain and bone development. Plus, hormones do (obviously) effect behavior and not all of those behavioral effects are bad! Having hormones on board can be confidence building in young dogs, so keeping them intact longer can mean better protection from anxiety based issues that are related specifically to a lack of confidence.
I bet you weren't expecting a birds and the bees conversation today, but there it is. I hope that for those of you concerned about mounting in puppy class, this eased your worries. And I hope you have a better understanding of why we wait to alter our dogs now as well.
As always, if you have questions about your pet's behavior, you know where to find me.
Here's Penny, the blenheim (brown and white) Cavalier King Charles Spaniel trying to enjoy a quick sniff while having her estrus status assessed by Neo (the black and tan) Cavalier King Charles Spaniel. He's an adolescent male, so this isn't unusual behavior. Penny is spayed, however, so her patience with this behavior is admirable. (Photo credit: Julie Skeen)