UK Safe hay?

Hi guys, I'm posting this here because it doesn't really apply to the US hays. I feed my pigs Oxbow timothy, but I'm going to make them a hayloft and thought it would be good to line it with cheaper hay so the piggies could pee on that and eat the timothy. I found a local-ish farmer that can sell me horse standard hay, a mixture of timothy and ryegrass, for £3 a bale! Wow! Do you think this stuff would be safe providing it's dry, non-musty etc? Nutritionally it wouldn't be that great but it's just a 'liner'. Also, I can collect a fair amount of long stemmed wild grasses from the edge of my Mum's garden over the summer period to feed fresh to my piggies. Are all types of grass and their seedheads in the UK safe? This seems a silly question, but I'd hate to go ahead without asking and end up harming my piggies.:sad: I looked at rabbitwelfare.org, and they have a picture of one kind of wild grass I recognise, but no others. I checked on GL and ryegrass is lower in calcium than timothy, so that shouldn't be a worry. Knowing my piggies, they will eat all the cheap stuff and pee on the healthier and expensive imported hay! If anyone knows about humidity levels of horse hay and how good they are for piggies I'd also appreciate your input, since the farmer started talking about humidity levels, but I didn't really understand what they meant for piggies or storability of hay.

Thanks in advance.