What is involved and what might it cost to fix a hernia in a yearling?

They basically push the intestines back into the body cavity and suture the abdominal wall back together. Sometimes mesh is used to help reinforce the abdominal wall at the site. If the intestine has been compromised due to prolonged non-treatment, a portion of it may need to be removed as well. Cost varies hugely from vet to vet and depending on what will need to be done in his specific case, so the only one that can give you an estimate would be the vet who does the surgery. I would guess not less than $500, probably closer to $1000 for a simple repair. The more that needs to be done to fix it, the higher the price goes. Prognosis depends on how successful the repair is. He could be fine for the rest of his life, or could have recurrences.