How to Tell if a Dog Is a Girl or Boy

Taking Extra Care When Checking a Newborn Puppy

Wait several weeks to thoroughly examine a newborn puppy. It becomes easier to determine the sex of a puppy as it ages. Try to wait at least 3-4 weeks before checking in order to increase your chances of making a correct determination. It will be easiest to wait until a full 8 weeks have passed, since after 8 weeks the genitals of male puppies should be fully visible. If the puppy still has its umbilical cord, look approximately 1/3 inch (1 cm) behind the cord for the puppy's penis. Within the first few weeks of a puppy's life, the penis will look like a small raised lump in the middle of the puppy's belly. Unlike male puppies, female puppies do not have any genitals on the belly itself.

Handle the puppy carefully. Newborn puppies are fragile, so you'll need to be especially gentle while handling them. Wash and dry your hands before picking up a puppy. While handling the puppy, be very gentle and very steady to avoid accidental injury. Make sure that the mother dog is comfortable with you handling her puppies. Some mother dogs can become aggressive if someone unfamiliar touches their puppies. If the puppy or the mother become distressed when you handle it, you should return the puppy to its mother and try again at another time.

Keep the puppy warm. You should perform the check in a warm area to prevent the puppy from catching a chill. Also make sure that your hands are warm when you pick it up. Young puppies can easily become sick if they get cold. To the same end, you should only handle the puppy for 5 to 10 minutes. Keeping the puppy out for longer than that can cause it to get too cold. If the puppy begins to shiver or cry, you should immediately return it to its mother's side or to a heated puppy pen.

Rest the puppy on its back. Either place a clean, soft towel on a sturdy work surface or do the check while holding the puppy in your hand. Carefully pick up the puppy and lay it on its back, thereby exposing its belly. Holding the puppy safely on its back in your hand can only be done if the puppy is small and docile enough. Make sure you securely support the puppy's head while holding it on its back. The towel should be warm. If necessary, throw the towel into a dryer for a few minutes before placing the puppy on it. Do not use towels that are cold, hot, or wet.

Differentiate between the penis and the umbilical cord. One of the most common mistakes made when sexing a small puppy is thinking that the umbilical cord is a penis. While both will look like small lumps on the puppy's belly, the detached umbilical cord (navel) will be just beneath the rib cage, while the penis is further down between the legs. Moreover, remember that both sexes will have at least one bump since both will have a navel. Male puppies will have a second bump in between the navel and the legs. Male puppies, by contrast, will only have one opening under their tail, while female dogs will have two. It's best to rely on a vet, breeder, or other professional dog handler if you want to sex a very young pup.

Checking the Physical Attributes of a Dog

Examine the dog for external male sex organs. Identify the penis and scrotum of male dogs by looking at the area between the belly and the tail. In older dogs these sex organs will be very visible, while they may be small and almost non-existent in young puppies. The scrotum should be just below the anus, almost directly between the hind legs. If a male dog has been fixed, meaning its ability to reproduce has been eliminated, it will not have a visible scrotum.

Look for external female sex organs. If a dog is female, you should be able to identify her vulva while she has her belly exposed. Gently lift the dog's hind legs apart until you can see the anus. Above the anus and between the dog's legs, you should be able to see a leaf-shaped structure. This is the female dog's vulva.

Look for the physical signs of pregnancy. One sure fire way to identify that a dog is female is to determine that it is pregnant. The signs of pregnancy include having a very large belly that appears despite no change in diet and, of course, the physical act of giving birth.

Avoid using other physical traits to identify sex. It can be tempting to try to find other traits to use as sex markers. However, any differences that may exist would be very subtle and hard to identify unless you are an expert on the dog's breed. Because of the subtlety of physical sex differences in different breeds, it's best to use other markers. For example, both male and female dogs have nipples, so assuming that a dog is female based on that alone will not work. Also, just because a dog is large for its breed or has a lot of muscle tone, that doesn't mean it is male. Size differences are minimal between male and female dogs.

Noticing Behavioral Differences

Watch urination habits after the the dog is at least 6 months old. Young puppies urinate in identical manners regardless of which sex they are. However, after 6 months most male dogs will lift their legs while urinating, while female dogs will continue to squat. During the first few weeks, puppies will not be able to control their bowel movements or urination at all, so it is useless to use urination stance at this point. Even after the puppies are strong enough to stand and control their habits, all puppies will squat while urinating for the first 2 months. Many male puppies need as many 6 months before developing the urination habits of adult dogs.

Be on the lookout for marking. Once male dogs are a few months old, they may begin to mark their territory. This is a pretty good behavioral marker of sex, because female puppies lack this instinct. The urge to mark his territory will be especially strong in male puppies who have not been neutered. Neutering a puppy will greatly reduce this urge. The exact age when male puppies begin to mark will vary from puppy to puppy, but most will start between 2 and 6 months. A dog that urinates quickly in many different locations is likely marking, especially if he intentionally urinates after thoroughly smelling each spot. Dogs that only urinate once or twice generally aren't marking, even if they stop to smell many different spots during a walk.

Watch for signs that the dog is going into heat. Female dogs who have not been spayed will go into heat on a semiannual basis. The first heat cycle will occur when the puppy is between 6 and 10 months old and each cycle will last for approximately 3 weeks. The signs that a female dog is in heat include changes in behavior, the vulva swelling, and discharge coming out of the vulva. Behavioral changes that a female dog may exhibit during their heat include jumpiness and clinginess. Female dogs in heat will produce a vaginal discharge that can be clear, brown, or bloody, depending on the point in their reproductive cycle they are in.

Don't use personality or general behavior as an indication of sex. Both male and female dogs can be equally affectionate, defensive, active, and calm. These aspects of their personality do not indicate anything about a dog's sex. For example, even mounting and humping, which is behavior that is generalized as a male trait, is often exhibited by female dogs.