Female dogs are called "bitches" and normally come into "heat" or estrus every 6-7 months on the average. This mating "season" usually lasts for three weeks at a time and can occur at any time of the year. The smaller dogs often come into their first heat before the larger dogs, which varies from 6-14 months of age, and ovulate fewer eggs than the larger breeds. There are as many different individual variations in the bitch's cycle as there are in a woman's cycle; however, the pattern tends to be repeated.
There are four stages to the bitch's cycle; proestrus, estrus, metestrus and anestrus. Proestrus begins with the appearance of a swollen vulva and a bloody discharge. The discharge can be copious at times and usually lasts for 4 to 9 days. Estrus is the true “standing” heat in which the bitch will accept the male for breeding purposes. The discharge is more yellowish than bloody and lasts for 4 to 13 days. The metestrus and anestrus stages are both periods of ovarian inactivity with no outward physical signs.
One example of individual variation is the bitch that constantly cycles every 2-3 months. This is usually called nymphomania because it appears that the bitch is constantly in estrous. Another individual variation is the "silent" heat in which there are no outward signs of estrous. These and other variations make it difficult to predict when exactly to breed the bitch. Performing smears of the vagina cytology during the proestrus stage can be helpful in determining the best time to breed. Often the best judge of the ideal time to breed comes from the experienced male dog or “stud”. In most cases the bitch is bred at least two times during the estrous cycle on alternate days. Occasionally, hormones can be injected into the bitch to improve the odds of a successful breeding.
Once fertilization has taken place and implantation has occurred the pregnancy period starts. There are only a few methods available to confirm that a bitch is pregnant. A radiograph can be taken after 45 days, as there is enough calcium present in the developing fetus to be recognizable. Palpation of the fetus after 21 days is possible but not always reliable. Ultrasound can detect the fetus reliably after 19 days.There is a relatively new chemical test that has been developed that is reliable at an even earlier time of pregnancy. In the dog gestation is approximately 62 to 65 days and the size of the pups is determined primarily by the bitch.
The delivery process is called whelping. Difficult deliveries are more likely to occur with the small breeds than with the larger breeds. First time mothers tend to have a more difficult time delivering the first pup. Little if any pain is evident in most cases of whelping. Instinct plays a big role in the whelping, nursing and weaning processes. The milk supply can start anywhere from a few days before whelping to a day afterward. The weaning from mothers milk can start as early as 3 weeks of age on up to 6 weeks or more of age.
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