Puberty
Bitches
In general, a bitch can start her first estrus, or "heat" between the ages of 6 months to 18 months. If you know when her dam first went into heat, that will give you a good indication of what to expect with your puppy. It is often felt that the larger breeds take longer to enter heat than the smaller ones felt, but familial patterns, if known, are a more reliable indicator.
The first signs of estrus include: a small amount of clear discharge, a modest swelling of the vulva (the external genital fold), and increased licking of the area. Some bitches have a shortened attention span. This period can last from 4 to 14 days. Other dogs will show an interest in licking the area (as opposed to just smelling it) as well.
The next stage includes bloody discharge, which can be anything from a few spots of blood to leaving a trail behind as they go, and increased swelling of the vulva. The nipples will enlarge somewhat. This period can last anywhere from 4-14 days as well. At the end of this stage, the vulva is at maximal size.
At this point the bitch is fertile and ready to be bred, and will accept male dogs. This stage lasts for several days. After the first heat cycle, the bitch's vulva and nipples will shrink down, but not to the puppy size that they were before.
However, there is much individual variation. Some bitches can show little or no sign of being in season throughout much of their estrus cycle. Some will always accept male dogs (even when they are not yet fertile) and others never accept them.
Spaying is generally done when the bitch is not in season. The increased vascularity (higher blood flow) in the organs makes the operation more risky. In addition, such an operation would alter the balance of hormones in the dog's body rather abruptly, a potential source of problems. However, it can be done, and often is if the bitch winds up unintentionally pregnant, for example.
Dogs
Male puppies are born with undescended testicles, just like human males. Somewhere between 4 months to a year, the testicles will descend, although you should be able to feel the testicles from about 7 weeks onward. At about this time the levels of testosterone are peaking. An intact male dog between 10 and 12 months of age has about five times the testosterone level he will have in his final adult intensity, if he is not neutered!
Male puppies will urinate like female puppies (by squatting) until about the time their testicles descend, and then will generally start to urinate standing up. Initial confusion is normal at this stage: be prepared for the puppy to raise the wrong leg, try to raise both legs, try to walk at the same time, or even try to use people as a "post"! You can encourage him to restrict his marking by praising him when he marks an acceptable item and scolding him when he is not. Discourage him from marking when you are on a walk; get him to mark around your yard as much as possible. (Marking, as opposed to urinating, is when only a small amount of urine is deposited.) Neutering early may or may not affect this behavior.
If a dog has only one testicle, he is monorchid. If he has one undescended testicle, he is cryptorchid (unilateral); two undescended and he is cryptorchid (bilateral). Popular but incorrect usage calls the dog with one undescended testicle monorchid and two undescended cryptorchid. Granted, you may not be able to tell whether a dog is monorchid or has unlateral cryporchidsm without exploratory surgery. Undescended testicles often become cancerous and should be removed. Furthermore, such dogs should not be bred since the condition is hereditary.
Further Reading
From a MedLine search:
TI: Questions and answers on the effects of surgically neutering dogs and cats.
AU: Johnston-SD
SO: J-Am-Vet-Med-Assoc. 1991 Apr 1; 198(7): 1206-14
TI: Effects of neutering and spaying on the behavior of dogs and cats: questions and answers about practical concerns.
AU: Hart-BL
SO: J-Am-Vet-Med-Assoc. 1991 Apr 1; 198(7): 1204-5
TI: Gonadectomy in immature dogs: effects on skeletal, physical, and behavioral development.
AU: Salmeri-KR; Bloomberg-MS; Scruggs-SL; Shille-V
SO: J-Am-Vet-Med-Assoc. 1991 Apr 1; 198(7): 1193-203
TI: Implications of early neutering in the dog and cat.
AU: Stubbs-WP; Bloomberg-MS
SO: Semin-Vet-Med-Surg-Small-Anim. 1995 Feb; 10(1): 8-12
