Joint ill/navel ill - most calves with it have full or partial failure of passive transfer of maternal antibodies - either they didn't get enough/any colostrum, poor quality colostrum, or may have had difficult delivery, etc., that raised cortisol levels, resulting in poor absorption. In any event, they ended up with not enough colostral antibodies in their system to fend 'em off.
Being born into nasty, muddy conditions sets the stage - the bacteria can enter through the umbilicus(navel) - and studies with foals have shown that bacteria can also enter through the soles of the hooves; I've got no reason to think that it couldn't also happen with calves. When we were in practice and were called out to deliver a calf, we routinely sprayed navel and hooves with iodine, in hopes of diminishing the likelihood of the calf (or foal) developing navel/joint ill.
Most of these infections are E.coli - it's the most common bacterial species in that newborn's environment in most cases - especially if the cows are calving in the same lot where they've been fed all winter and they're slogging through mud up to their udders to get to the hay feeders - and the little calves are following mom.
A broad-spectrum antibiotic is in order, and probably a lengthy treatment period. Consult your veterinarian.