What is the best way to feed a pup with pretty severe pano?
Will you keep a puppy for breeding that has pano?
Have you seen any related issues later?
Does it run in certain lines?

I would feed a moderate diet.

"The cause of panosteitis is currently unknown. There have been many theories as to the cause of this disease. Originally, it was suspected that the disease was caused by a bacterial infection. However, several investigational studies failed to isolate any bacteria. In addition, the disease responds poorly to antibiotics, further suggesting a cause other than bacterial.

Other studies showed that if bone marrow from affected dogs was injected into the bones of healthy dogs, the healthy dogs would contract the disease. It has therefore been speculated that a virus may cause the disease. The high fever, tonsillitis, and altered white blood cell count would also go along with the viral theory. Another interesting twist to the viral theory is that panosteitis was first identified as a problem at the same time that modified live distemper vaccines became widely available on the market. Since wild distemper virus can be isolated from bone tissue, some researchers feel that there might be a link between distemper virus vaccine and panosteitis, however, more research in this area will need to be done before any serious speculations can be made.

Another theory is that panosteitis might have a genetic link. Because of the greatly increased incidence in certain breeds and families of dogs, it is very likely that there is a genetic component involved in this disease.

Lately, there have been some claims that nutrition, particularly protein and fat concentrations in the diet, may have an impact on the incidence of the disease. But here again, more research needs to be done to substantiate these claims. Most likely this is a multifactorial disease that has several different causes including viral, genetic, and possibly nutritional."
http://www.peteducation.com/article.cfm?c=2&aid=466

My foundation bitch had pano. I didn't know about keeping pups lean at the time. I haven't had a single case of pano at my house since then. I feed ProPlan Performance.

I recently had severe pano in one of my pups, now fine. She only had it for 3 weeks. I've always found adding glucosamine, chondroiton AND MSM along with Vitamin C to the diet while crate resting pup helps so much (don't skip the MSM, I buy pills with all but the Vitamin C in one pill).

After her pano was gone, I fed as usual (more than some breeders do) as I believe in feeding for bone. She's 9 months now with fantastic bone and no repeat in the pano. I only cut back on food until all pano symptoms are gone. Just how we've handled it here. Never had in in these lines before, so I'm keeping pup. If we constantly reproduce it, then I'll reconsider this line. But over the years I've found it spontaneously appears out of nowhere and then you'll go years without it. I find the post about a virus very interesting, makes sense.

One pup that had it years ago from another line is now retired and serves a post trauma vet as a companion. She's now 9 years old and never had and issue since pano as a pup. We've had one or two others along the way that went to pet homes, never an issue later.