Oh my goodness - I have been following this thread for a while but I have only just realised you mean your pigs are completely outside - with not even a shed for protection.
I don't mean to be rude but you are very lucky to still have any live pigs at all. Pigs are highly susceptible to excess heat or cold, drafts, damp, etc - things which can not possibly be prevented in a hutch. Not to mention the risks of predators, parasites, vermin etc that have already been mentioned.
Please don't make the mistake I did - my first ever pet was rabbit who lived outside in his safe hutch, which we believed was warm and comfortable because we covered it in bad weather. That poor baby died at less than two years old of pneumonia. So much for safe, well insulated hutches.
A shed alone is not going to be good enough either, as they are not well insulated. A colleague of mine keeps his pigs in the shed over winter but still complains that their water bottle freezes! Having slept in one myself I can tell you from personal experience that sheds are not warm, or draft free, or safe from vermin or insects etc.
Seriously, please don't get offended by people's comments on here. I know in the UK it is still considered normal for certain animals to live outside but that doesn't make it right. There is also a lot of bad info, in books, in pet shops, etc. It is so easy to make mistakes. Sadly, most people don't realise these mistakes until its too late and their beloved pets are dead. I found out the hard way - I sincerely hope you don't have to. Please, please get your animals into a proper, safe environment asap.
