Before any of my bulls are sold they get a BSE which includes a semen test and measuring/examining the testicles by the vet. Almost always if there is any sort of abnormality in the semen test in the form of white blood sells or other issues there will be a corrisponding issue with the testicles, usually enlarged due to infection. Also any bull i have that has a signifigant differnce in size or too small testicles gets banded instead of being seedstock to my customers. I would suggest a vet check and semen test to make sure he is viable, if not, often an antibotic will clear it up. Don't know how cold it gets where your at but frozen nuts are also always a possibity.