Female dogs are as individual as female humans but there is some behavior that is common to unspayed female dogs. The heat period of dogs rolls the whole sexual reproductive phase of dogs into a few weeks once or twice a year.
In stage one the dog's vulva begins to swell. She may seem more affectionate to humans and male dogs but more aggressive to other females. She may seem distracted when doing obedience or other work. She may eat more or go off feed. She will usually spend a lot of time licking herself and other dogs in the household will be interested in smelling and licking her also. An experienced stud dog will not try to mount her now but wants to spend a lot of time near her. Males near her may fight and other females may act differently to her depending on her rank with them. If she is submissive they may punish or attack her. If she is the dominant dog they may avoid her. This stage is comparable to the premenstrual period in humans. This stage lasts roughly a week.
Stage 2 is when the dog begins to bleed. This is the stage that most dog owners notice first and think is the beginning of heat. Some dogs bleed a lot, some very little. Her vulva will still be swollen. The bleeding is not harmful to the dog. Her behavior really begins to change now, although each dog is different. She may flirt with males and even other females. She may actively try to escape and find other dogs. If she is a dominant dog she may mount other dogs, people or even other animals. A stud dog will be very interested but the experienced one will not mount her unless she invites him and stands for him.. A female interested in a male literally sticks her butt in his face. At this stage, while she will wrestle and play with the male, allow him to put his head and feet on her and her tail will move to one side [called flagging,] when he smells her or trys to mount her, she generally will not allow him to penetrate her. Some females will allow males to mount and penetrate them in this stage though, and some males will force a smaller, less dominant female in this stage. Males will be extremely excited around a female in this stage and may bite or attack humans if they try to interfere. Children should not be left alone with dogs interested in mating and if they play with female dogs in heat they should wash their hands and change clothing before going around other dogs. Even neutered male dogs may be interested in a female in this stage of heat or later and some will even try to mount them. Females in this stage of heat may not eat well and they may become more aggressive. Some appear anxious and extremely clingy and affectionate with a favored person. Or they may suddenly become very attached to someone in the home they ignored before. Female dogs in the same house or kennel will tend to come in heat at the same time and with all the hormones raging, great care is needed to keep fights from breaking out. Usually this stage of heat lasts about a week.
If you do not want puppies your dog must be confined or on leash with a responsible adult at all times from this stage of heat until it ends. Don't leave the dog outside alone for any length of time, even in a fenced yard. Other dogs may jump the fence. Females become great escape artists at this time and even if they never leave your yard any other time, they will roam off when in heat. Housebroken dogs may make small puddles around the house. They are marking to attract males. Outside they will be doing this too, and males will smell it for a long distance.
The third stage of heat is when the bleeding stops and ovulation occurs. This stage may go unnoticed or the owner may think heat is over. Males around the dog will be extremely interested. They will not eat or even rest much while the female is around. She will also be extremely interested in them and will stand still and move her tail away from the vulva area whenever a male gets near her. Males will mount a female in this stage almost immediately. Extreme care is needed at this point to keep the female from being bred if you don't want puppies. If you want to breed her, now is the time. That is the subject for another article. After a dog ovulates the eggs remain good for 3-5 days. In a few days the cycle starts to wind down and if the female is not bred, her behavior should return to normal in a week or so. These stages of heat vary in length from dog to dog.
If your dog got bred during heat you may notice subtle behavior changes almost immediately or the dog may seem normal for a while. Some dogs actually experience morning sickness, although most just seem to get a big appetite. By the 4th or 5th week of pregnancy the dog may start to show, there is some enlargement of the nipples and she may want to sleep more. Some dogs don't let anything change their activities until they get to the last week or so. In the last week or 10 days of pregnancy the maternal hormones kick in. [ Gestation is about 63 days] The dog may look for a "den", a quiet dark spot. She may scratch and root in the "nest." You should set up such a den for her but take note of other spots she may be disappearing into. She may seem anxious and a little uneasy, especially if it's her first pregnancy. She may be a little short tempered with kids or other pets.
I will not cover the whelping or birthing process here as it is very involved. But immediately after giving birth the female dog is generally very anxious and protective about her puppies. Keep kids and strangers and other pets away from the litter. She may attack without warning if someone gets too close to her pups. Most dogs quiet down in a few days and in a few weeks will be happy to let you have the pups for a while.
Female dogs who do not get pregnant sometimes have what is called a false pregnancy.
They go through all the hormonal changes right down to making a nest. They may steal other pups or baby animals to mother or treat toys like pups. This generally lasts a few days, starting about the 56th day from her heat. They will then return to normal.
Female dogs that are spayed early, before their first heat, don't generally have behaviors that are much different from a neutered male dog. Female dogs who have had a litter may seem a little more maternal in their actions, but if they have been spayed their hormones are gone and the behavior is a habit or learned behavior. I do believe there is a slight difference in the behavior of unspayed females and whole males. Once again, each dog is an individual. The behavior isn't always favorable, whole females fight each other much quicker than neutered females, and in my opinion, many whole females are more aggressive with the same sex than whole males are with each other. Their hormones may make them unstable for work during their heat and pregnancy periods. They do seem to be a little more patient and tolerant of children and other baby animals, but not every female is that way. Compared to whole males they may be less aggressive, when they are not in heat or nursing. For a pet or working animal, it is much better to have the female spayed and avoid hormonal upheavals.