Help my friend with his piglet problem

He has have one blood line in his herd that when sows have little ones they get stiff swollen joints piglets would anyone know what that's from?

Mycoplasma hyosynoviae from the Pigsite link above is quite common in the environment. Many pigs are resistant. If treated with antibiotics quickly those pigs will finish just fine. If not, it will kill around 20% of those infected. All of our growers that we buy locally don't get it. Litters we have gotten two years in a row from out of state have been affected after we received them. Its too bad because they are such nice looking pigs, but the vet bill and cost of antibiotics the last two years really cuts into profitability.