5 month old puppy has one testicle noticeably smaller than the other?

(Show dog / Stud dog; Will service until 5 years. Breeder is very involved with healthy dog breeding. Parent's have had genetic mapping, neither have any heritable genetic defects. The puppy will undergo mapping at one year.) My 5 1/2 month old Australian Shepherd puppy has one testicle noticeably smaller than the other. Vet noticed this, at his last check up / final immunization 5 weeks ago. She advised me that the testicle has descended, and has no obvious abnormalities, other than the one testicle being about half the size of the other. I was told to watch it, and bring him in if the condition doesn't change or there are any signs of discomfort. My question is what do you think it could be? I inspected it today, and it is still much smaller than the other. The breeder and their conformation assistant/trainer noticed it today as well. I'd bring him to the vet and ask - but it'd be around a week, since it is not an emergency, to get an appointment, and have the breeder sign it off to be paid for by them. What do you think it could be, and does it require my immediate attention?Both his parents were tested for all sorts of diseases. If required I can go pull his papers and tell you specifics. Parents have been mapped and have no heritable genetic abnormalities. He doesn't go to be certified as a stud dog until 7 months. There is no inflammation, and he doesn't have any pain when they are handled. I am paranoid when it comes to my dog, and will take him ASAP to a vet, if required; I'm just not sure if it's that serious and if it can wait until he is 7 months and goes to a specialist to evaluate his health and ability to Sire puppies.Father: MDR1 Normal/NormalCataract Gene - Normal/NormalElbows/Patellas - NormalPRA PRCD - Normal OFA Good. CERF CLEAR. Mother:MDR1 Normal/NormalCataract Gene - Normal/NormalElbows/Patellas - NormalPRA PRCD - Normal OFA Good. CERF CLEAR. AS-19727G25M-PIHIPSJul 16 2004Aug 9 200425GOODAS-EL3075M70-PIELBOWApr 14 2008 May 14 200870NORMALAS-PA257/70M/P-PIPATELLAApr 14 2008 May 14 200870NORMAL - PRACTITIONERMAS-226CERFApr 11 2009 Apr 11 2009 *82TESTED: 04,07,08,09

It could be that they haven't fully dropped yet.... But just in case you should go see a vet. because of the chance that one is "swollen" or something not just bigger

Um, quit worrying about your dog's balls so much. ;)Seriously though, if it doesn't change and nothing is physically wrong (you're only worried about the aesthetics of your dog's balls), you could have one removed and a fake one put in to match the other. But seriously, they're balls dude.

As long as both testicles have descended, it's a non-issue. The vet said keep an eye on it...then keep an eye on it. No biggie.

Well, it's testicular atrophy. Why it is happening, I don't know. The problem that can arise is if the atrophied tissue becomes necrotic - starts to decay. Then he'll have a life-threatening condition. Were the parents both tested for Brucellosis before being allowed to mate for this litter? Were the puppies in contact with other dogs in the breeder's home or kennel? This puppy should be dropped from any future breeding program. Not only is he likely to be infertile, but, unless the cause of this physical abnormality can be determined, this condition may be passed on to any offspring.

Personally I would wait until your 7 month check, since it sounds like you'll have a specialist evaluating him. Though I have no idea how or why you would get a dog "certified" to be a stud dog, especially at 7 months old. I've been showing dogs since I was 10 years old and never heard of a stud dog being "certified" ; health tested yes, but not "certified". And health testing you don't do until the dog is fully developed and 2 years old. Perhaps this is a working dog or Australian shepherd thing?If he still has the issue at a year old the I would likely neuter him, after speaking with the vet. Chances are that this issue will be passed on to his pups and he could have an increased risk of developing cancer. Since you've already seen your vet and they pointed out the issue, you should be able to call them and discus the various potential health and breeding issues without having to bring him back in. You'll probably have to leave a message with the receptionist to have the Dr call you back.