When I first got started this was the advice I was given...use a larger female for larger litters & easier whelping, with a smaller stud to give smaller puppies. When I got serious about improving the breed, and specifically my program, everything about my initial understanding went out the window. Now I wouldn't hesitate to use a male that is bigger than my female if I know enough about the lines and he has the specific qualities I am looking for.

To take a shot at the original question, I think peer pressure is why the larger males aren't popular. Smaller males are what "everyone is using" and since most don't study enough to know it might not be best...they just do what everyone else is doing. I also think this is why we see so many poorly proportioned puppies. Small males and large females often don't throw a well proportioned puppy. In my experience it often produces a longer body with shorter legs, and a smaller head with large ears. These two proportion problems are very common in the breed nowadays.

thoughts on size
 

You are very correct that no matter what any given sire or dam's size may be, the genetic work up is the sole determining factor in what qualities offspring will obtain. Since several, as the above poster noted, genes control multiple characteristics, not every offspring will inherit the same traits. This is why litter mates can often vary in size and color regardless of the breed. With that said, a precise knowledge of exactly what characteristics any given offspring will be is impossible to really know other than the dominate genes that basically define a breed.... you might be able to use geneology, DNA, ect to help, however, a particular genotype my show up in one puppy and never show again.... it just isn't a perfect science by no means....
But, to shed some light on the original poster's question... Each dog has the exact same chance to throw equally sized offspring. Will they... that depends largely on the second pair of genes introduced.... IMO, it has a lot to do with buyer perception. Most clients are looking for that teeny tiny Yorkie they've seen somewhere.... Take for instance two identical pairs: They see a 4lb female and 2lb male along side another pair whose dam is 7 lbs and the same sire is used. Most automatically want a puppy from the 1st pair, if size is the only factor......It takes a great deal of discussion to convince prospective buyers that paring one may have puppies much larger than pair two.... I've had several of these conversations and to tell you the truth so much is lost in translation, I often just give up. When I am asked to explain, I work with this genetic anomaly..... "If you know anyone who is left handed, most likely neither of their parents were. Generally, this is a trait that skips one or more generations....and is often present only on the maternal side.... It is the same as any other genetic trait, some show up in every offspring and some skip one or more generations (or litters), some show up only on the maternal side, some the paternal side... nature rules that show and we can only do our best to use the information we have to predict a particular outcome. We have one son who is a lefty, no one else in our family is with the exception of my grandmother. My grandmother had 10 children, 22 grandchildren, and 15 great grand children.... so far my son is the only lefty.... go figure... Thus I never give anything other than an educated guess when it comes to characteristics of a puppy leaving my care prior to 25 weeks..... and I leave it at that.....

size
 

I have no problem using a male of 6 or 7 pounds..size is not my first priority...but there is no room in any breeders program for an oversized pet quality stud...and that goes for a bitch also..IMO...

First and foremost, you cannot accurately speculate the size of pups that will be produced based on the size of the dam and sire alone...you have to consider the size of the dogs down the line as well.

Secondly, you can't take the chance that a larger male *could* throw small. It could happen, but what if he doesn't? If the pups are not small, then you've endangered the life of the female that will be carrying/delivering them.

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The bitch determines the size of the pups at birth so the size of the male is not my main consideration either. The size of the adults will be determined by
the genetics of the two lines that you are putting together. In choosing a stud your main concern should be quality not size. I personally wouldn't breed a male that I couldn't take into the ring and that would include an 8 pound male.

So then Tami, would it would not matter if you bred a 15 pound male from a line of 15 pound dogs to a 5 pound female?
(speaking strictly of what would be considered "safe" for the female to carry/deliver)
All of the warnings against breeding a small girl to a much larger male are being made in vain?

I'm getting some very good answers and information here but I think some have missed what I wrote in post #3:

I never said to breed a large male to a small female...that's not what this thread is about. What I said was if you have a larger, quality male why don't breeders use them with an appropriate sized female if you know he came from standard sized lines? If you bred a 'larger' male with a larger female (or a brood bitch as some call them) then why would it be wrong? If both come from standard lines but happen to be throwbacks then why is it bad? It seems I'm seeing more and more that breeders "think or feel" the larger males shouldn't be used for breeding. But...I "think and feel" there are some beautiful males being overlooked because they weigh more than 2 or 3 pounds. I, for one, prefer a solid, sound structure over a fine boned male.

I wouldn't breed a guy that was oversized anyway but from all of my research the size of the female, the number of whelps in utero, their placement, and the amount of resources determines the size of the whelps when born. Alot of males are larger than females, not only in different breeds but in nature as well. The most important consideration when choosing a stud should not be his size but health, temperment and conformation to the breed standard.

I can not say why this breeder feels that the 7-9 lb female is ok for breeding but not the male. I would question the ethics of a breeder that uses an over standard female bred to smaller males...what are they trying to produce?

In my opinion this double standard should not exist...I like both my males and females to be 5-7 lbs. I agree there are some smaller males that are nice representations of the breed, but I also believe that if we continue to consistently breed 5-7 lb adults (male and female) then it will help to develop more consistency in size within the breed.

I agree in that I like some substance to my yorkie, after all they were bred to be ratters and were not meant to be the smallest breed. I would breed both a 7 pound male or a 7 pound female. I wouldn't be concerned about size too much unless the pups consistantly grew to be oversized. If the pups were outside the standard than I wouldn't repeat the breeding, same goes for bad rears, poor ear set or any other fault.

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I would not breed a yorkie over standard so no I would not mate a 15 lb dog to a 5 lb female. That said, while working in a clinic a 12 lb yorkie was accidentally bred to the neighbors 40-45 lb terrier mix. We monitored her pregnancy closely as the vet I was working for thought they would get too large. Well they didn't...she free whelped 3 full term puppies. The owner of the yorkie kept one and she grew up to be a 35 lb dog. So no I do not think it would endanger the female. In my experience larger females whelp larger puppies compared to smaller females...no matter the weight of the stud used.

They use the larger females in hopes of getting larger litters, but the smaller male in hopes of getting some smaller puppies.

I too prefer mine in the 5 to 6 pound range. But I understand their line of reasoning.

Yea it's all about the money, big litters equal more profit. This is how we get such diversity in size within our breed. People than feel robbed when their supposedly 6 pound pups grows up to be a 15 pound dog.