My name is ***** ***** I’ve been involved professionally with dogs in the health and behavioral fields for over 18 years. I've also been breeding rottweilers for over 18 years. It will be my pleasure to work with you today. It seems that Dr. Pete is not available.
If the dam developed mastitis at 3 weeks of age, that is about the same time the pups should have started being weaned from the mother. So at that point, while they may have still been nursing a bit on mom and also getting supplemental bottle feedings or formula in a bowl, it really should not have affected their growth that much since they should have been getting a high quality kibble. I'm hoping they were feeding puppy food because giant breeds need a high quality puppy food for large breeds. This is not necessarily high protein. . Read more on proper nutrition for large breed pups here;
This site discusses it in an easier to understand format.
That said, even though your pup is one of the smaller pups, I don't feel he would have any long term problems due to the fact his mother had mastitis around the time he would have started weaning. As for his final adult size, often smaller pups at 8 weeks of age end up being larger then the larger pups. May people will shy away from the smallest pup in the litter, but I've found that as long as there isn't a health reason such as organ dysfunction that caused the pup to be the smallest, they tend to catch up to their siblings as they mature and often are larger as adults.
In every litter you have larger pups and smaller pups and often a runt. Since they should have been weaning when she developed mastitis, I doubt there will be any long term developmental issues as a result. If they had been younger when the mom developed the mastitis, I would have been more concerned, but at that age, they are not as susceptible to the toxins and would have been removed from the mom at the time the mastitis was discovered. I do think you should pay special attention to diet and exercise for your pup. Excessive exercise in a growing pup can lead to joint issues as well.
I hope this information is helpful to you. If you need more information or clarification, please reply and I'll get back to you as soon as possible. If you are satisfied, please take the opportunity to rate.