Why do you think that your dog must be bred?
Is he currently being shown? Do your know what must be achieved with your dog before he should even be considered for breeding? Do you realize that life with a stud dog is not all that easy
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If your pup's sire is 138 lbs he is either overweight or oversized. That's usually not in the standard size for a Rottweiler. What titles has the sire achieved?
Your pup may take after the dam's side and just be a good average size for a Rottweiler male. Bigger is not better with this breed. They are supposed to be a working breed and supposed to be able to run and move without discomfort.
Gina