This article is from the American Maltese Association website. However, the information below applies to all toy breeds, including Biewer Terriers.
https://www.americanmaltese.org/ama-health-information/12-weeks-worth-wait
12 Weeks Worth The Wait!
Credit: Sharon Pearson and Vicki Fierheller
American Maltese Association
Our American Maltese Association Code of Ethics states, “I will not sell a puppy before it has been given a veterinarian health examination and has received at least one inoculation against distemper, hepatitis and parvo. A puppy will remain in my possession until at least 12 weeks of age.” Why do we have this as part of our code? After all, pet stores and backyard breeders sell puppies at a much younger age, some even as young as 6 weeks of age!
One of the unique characteristics of toy breeds such as the Maltese is that not only are they very tiny in size as adults, but they are much slower to develop as puppies and retain many puppy traits for a long time. The best way to illustrate this is to compare large breeds versus the toy breed. By 3-4 weeks of age, large breeds will be playing and becoming quite mobile. At this age, their baby teeth are already coming through and they will be starting to eat solid food (weaning). Meanwhile, our Maltese are just starting to get up on their feet, have no teeth and are still relying 100 percent on their mother for food by nursing. At 8 weeks of age, the difference becomes even more noticeable. Large breeds are fully weaned with all their puppy teeth. First vaccinations are given and housetraining is well underway. Large breeds are ready to leave their littermates and go to their new homes. Maltese at the same age are just starting to wean and are likely still predominantly nursing on their mother. The adult teeth are just erupting and they are finally interacting with their littermates. Housetraining is in the beginning stages.
A few other facts to take into consideration: At 7-8 weeks, Maltese are harder to housetrain. Because they are so tiny at this age, their bladders are also tiny. This means they need to eliminate much more frequently than large breeds. For the pet owner, this means having to be more diligent (and that includes getting up in the middle of the night!) about taking the puppy to its chosen place. It is amazing how much difference a month can make. It is much easier to housetrain toy breeds at 12 weeks as bladder control has matured along with the puppy.
The weaning stage, which generally starts from 6-8 weeks of age in Maltese, can be a rather trying time. It is not unusual for puppies to decide they would rather continue to nurse than to eat real food! Sometimes it will take a few days to get the puppies to start eating well, unlike large breeds that chow down with the first bowl offered!
Certain lines of Maltese or very tiny puppies can be prone to bouts of hypoglycemia (low blood sugar) from the time of weaning to about 3-4 months of age, usually the result of not eating enough. By 12 weeks, Maltese are weaned, eating regular meals and usually past the danger of hypoglycemia. If there is still any concern about hypoglycemia, a reputable breeder will keep the puppy for a while longer.
Usually the first vaccinations are given at around 8 weeks of age. Some breeders like to hold off for an extra week or two, particularly if the puppies are slow to wean or the puppies are tiny.
Size is another consideration. Maltese should be 1.5 to 2 lbs. at 8 weeks of age. That is smaller than many of the stuffed dog toys out there! While adult Maltese are very sturdy, it is very easy for a puppy that size and with that level of coordination to become injured. Even a fall off a step could mean a trip to the vet. At 12 weeks, Maltese are around 2.5 to 3 lbs. While that may not seem like much of a weight gain, in actuality, it is an increase of one-third of the puppy in just a month! Mentally, Maltese need that month with their littermates and their mother. Littermates teach each other how to play and together they learn social skills. The mother teaches them manners. This interaction makes for a more well-rounded puppy. Puppies taken away at an early age can have a much harder time with canine socialization and may over-bond with their humans.
Breeders should start grooming lessons which, for Maltese, is all-important since they require grooming all their lives. A 6-8 week old puppy from a pet store or backyard breeder may never have had a bath, a brushing or its nails done, but by 12 weeks with a reputable breeder, the puppies will have had multiple grooming sessions. This paves the way for a puppy to enjoy grooming rather creating a battle with an inexperienced new owner.
A reputable breeder also knows the importance of socialization, and will expose his or her puppies to new situations, car rides and many other experiences that will make a confident, outgoing puppy. It is well worth waiting that extra month for that special puppy who is that much further along in development and social skills.