Get into a repro vet asap. If it's a mycoplasma bacteria and they treat it right away, they may be able to get his fertility back. Time is of absolute essence. Years ago, I used a young boy and then wanted to use him again a year later and no sperm at all. We caught it too late and never got him back. However, I've heard of others who caught it sooner and treated successfully.
"Two months of Baytril , tribulus 2 caps per day, flax seed w/lignans 1 tablespoon per day,both found at GNC store, Glycoflex the orignal formula. Then collect and see if he has improved , try this before you cut into him. This is all per my Repro Vet."
The above is from a 2010 posting, it's worth a try. There are several old threads on this. Search 'no sperm'. All the best!
Get a culture done asap and then go from there. Definitely would put him on a good fish oil, Vit E, Glyco Flex and IM A STUD supplement (Nature's Farmacy).