There is more involved in dog breeding than what you might think. Many first-time breeders are under the false impression that breeding dogs is an easy way to make money, a good way to teach the children the miracle of birth, or a practical means by which to get another puppy that will be just like either of its parents. These breeders soon realize that breeding is not as easy as they thought. In fact, it is estimated that 75% of first-time breeders do not attempt to breed again because of the cost, time, and work involved.
The only reason that any dog should be bred is for the betterment of its breed. Before any plans are made to breed, the dog should be proven to be of breeding quality, tested and proven free of genetic and veneral diseases, proven to be of suitable temperament for the breed, and it must be in good overall health. If your dog does not meet these criteria, which are explained in detail below, then he or she should be spayed/neutered and enjoyed as a pet.

Being of breeding quality consists of much more than two dogs being of the same breed, opposite sex, and fertile (able to produce puppies). You should familiarize yourself with the breed standard and learn to evaluate your dog(s) against it. The standard is a blueprint of sorts that outlines what a Rat Terrier should look like. These standards are written with the breed's original purpose in mind to ensure that the dogs can withstand the rigors of what they were bred to do. Prior to being bred, the dogs should be evaluated against the standard, preferrably by someone with experience in the breed. The best way to do this is in a competitive environment, such as conformation events, where they can be evaluated against other top specimens of the breed by qualified judges.
Additionally, being registered or having "papers" is not an indication of your dog's quality. Registries do not guarantee the quality of the dogs they register and do not restrict the breeding of those dogs. Registration simply means that the parentage of your dog is known and it bears no reflection on the quality of the dog.

Rat Terriers are known for their hardiness and the relatively low frequency of genetic disease in the breed; however, as the popularity of this breed increases, unfortunately so will the incidence of genetic disease. Just because these diseases are still relatively uncommon, it doesn't mean that they don't need to be tested for and avoided. A few of the diseases that affect RTs are patellar luxation, epilipsy, cleft palatte, color dilution alopecia (CDA), and thyroid abnormalities. Again, these are just a few of the genetically linked diseases that have been seen in this breed, but they have not yet been seen in as great proportions as other breeds.
In addition, any dog being bred must be tested for veneral diseases such as brucellosis. Canine Brucellosis is a sexually transmitted disease that affects both sexes. It may cause repeated spontaneous abortions in females, puppies to die soon after birth or be born dead, and males may also experience testicular atrophy and infections of the prostate gland or testes. Brucellosis can also cause eventual sterility and bone infections in both sexes. To test for brucellosis requires two separate tests conducted one month apart.
NOTE:A dog that appears healthy may be affected but not show symptoms of a disease. They can also be carriers of a genetic disease that may not affect that dog, but could occur in its offspring.

Since temperament is also inherited, a good breeding candidate should exhibit the typical breed temperament. Rat Terriers are naturally out-going and friendly. A dog that is aggressive, excitable, shy, or overly submissive should be spayed/neutered and never bred.

Prior to being bred, both the sire (male) and dam (female) should be in excellent general health. It is most important for the dam to be in good health so she is able to withstand the stresses of a pregnancy. Most experts recommend that a female dog be at least two years old before being bred. Dogs at this age are generally physically and mentally mature enough to carry and care for a litter of puppies.

The number one reason people give for breeding their dogs is to make money, whether it be to supplement their own income, make back the money they spent on their dog, or to get some extra money for the vacation fund. If done properly, breeding dogs is rarely a money-making venture. In fact, you can rarely expect to break even on your expenses. The costs of testing for hereditary and veneral disease, stud dog fee, veterinary care for the pregnant dog and puppies, advertising to find good homes for the puppies, budgeting for possible complications, etc. quickly add up to the hundreds, if not thousands, of dollars.

Breeding dogs also comes with its share of risks. Even the most experienced breeders often see complications with their dogs' pregnancies. It is not uncommon for some dogs to require a cesarean section to deliver their puppies. It is also not a rare occurrance for a dog and/or her puppies to die due to complications with whelping. Sometimes, dogs will abandon their puppies or the puppies will be orphaned and you will have to hand-raise them. Are you prepared for this possibility? Do you know how to feed and care for newborn puppies?
As the puppies grow, they will also demand more of your time, attention, and bank account. You will have to spend more time cleaning up after them, you will have to spend more money on dog food and veterinary care, and you will have to spend a greater amount of time socializing them and preparing them for thier new homes.
Using your dog at stud is also associated with many drawbacks. He will be more inclined to wander in search of females in heat and stands a greater risk of getting lost or injured. He will become more territorial and will be more likely to get into fights with other male dogs or mark his territory - both outside and indoors.

As a breeder, you are responsible for each and every life that you help bring into this world. It is your responsibility to carefully screen potential homes for these puppies to make sure that they will be loved and cared for properly. You must also be prepared to take them back at any time during their lives should the new owner find him or herself unable to care for them any longer. Are you prepared to keep and care for another dog or place it in another good home if this should happen? Additionally, it is your duty to ensure that your dog's offspring do not further contribute to pet overpopulation. Would you require that all new owners have their puppies spayed/neutered? Would you call periodically to check up on the puppies to make sure that they are being taken care of? Contrary to what you may have known previously, your responsibility to these puppies does not end when they leave your care.

Only about 39% of dog owners are even aware of the pet overpopulation problem. A fertile female dog can have up to two litters each year and the average size of a litter of puppies is between 6 and 10. Theoretically, one female dog and her offspring can produce 67,000 dogs in a six year period. Only one in five puppies stays in its original home for its natural lifetime.
No dog should ever be bred with the sole purpose of creating just pet quality puppies. It is estimated that 3.5 million "just pet" dogs are put to death in shelters across the country each year because there aren't enough homes and 25-30% of the dogs euthanized are purebred. That does not include those that are abandoned and succumb to disease, injury, or abuse. Many RTs are surrendered to shelters and rescues every year because of excessive and irresponsible breeding and irresponsible pet owners (for more info on rescued RTs, please visit Ratbone Rescues or Petfinder)

My dog is purebred, therefore I am obligated to breed him/her.

Being purebred and fertile (able to produce puppies) should not be the only criteria used to determine whether or not a dog is suitable to be bred. Just because the dog that you own is purebred does not mean that you are under any obligation whatsoever to breed him or her. Approximately 25-30% of dogs that enter shelters are also purebred.

My dog is wonderful and I'd like to have another just like him/her.

If your dog is so wonderful, why would you want to risk her health to breed her? The chances of getting another dog identical to yours either in temperament, personality, or appearance is extremely slim. Genetics is not in favor of such a thing happpening. Each dog is an individual, and it would be unfair to expect a puppy to be exactly like his or her parents.

Breeding dogs is an easy way to make some extra money.

Of course it's an easy way for you to make money - the dogs do all the work! In fact, if done properly, you cannot expect to make very much money breeding dogs (you'd be lucky to break even). The parents must come from superb bloodlines from a reputable breeder. They must be proven in conformation or other competive events to show that they have something wonderful to offer to their breed. They must also be tested for common genetic diseases and given proper certification. Just because the parents appear to be healthy doesn't mean that there isn't a serious health problem hiding in their genetic background. The costs of caring for a pregnant dog quickly add up, as do the costs for caring for a litter of puppies. The total cost involved could run into the thousands of dollars.

I want my children to witness the "miracle of birth."

If you want your children to witness the miracle of birth, there are other ways to do it that won't be at the expense of the family pet. There are several nice videos and nature documentary films that cover the topic nicely. The children need not experience it in real life to appreciate it. Besides, dogs usually give birth in the middle of the night or in quiet privacy. The mother dog may become distressed if too many people crowd her during delivery, which may cause problems.

If my dog gets pregnant, I won't have any trouble finding homes for the puppies.

In your own fantasy world, maybe not. In reality, finding good homes for puppies is extremely difficult, especially for those of mixed origin. Giving them to anyone who comes to your door and is willing to take them or hand over cash does not constitute a truly good home. In fact, only 1 in 5 "free to good home" pets actually make it into a good home. That means, statistically, that in a litter of 5 puppies only 1 may actually end up in a good home. What happens when one of the new owners of one of those puppies call you six months later to say that they no longer want the dog? Would you be willing to take him or her back? What happens when one of the new owners of one of those puppies calls you to tell you that they just found out that their puppy is showing signs of a genetic disease? Would you take the puppy back or refund the purchase price? These are all things that need to be considered. Every single puppy that you help bring into this world is your responsibility until it leaves this world.
Also keep in mind that each good home you find for one of your puppies could mean one less good home for those in shelters looking for homes. In less than a year's time, your dog's puppies will be old enough to have their own puppies unless you require that they be spayed/neutered. This means even fewer homes for those in shelters, and the greater potential spread of genetic disease in the breed.

If after considering all of the information here you still want to breed your Rat Terrier, I urge you to please approach it in a responsible manner. Get involved in breed clubs, both local and national, attend dog events, study the breed standard, and find a good mentor with experience in the breed.