Fresh grass can cause huge problems - fresh grass, particularly fast growing spring grass,
on unprepared digestive systems can cause bloat, and bloat can be fatal.
If their gut is not used to fresh grass and they haven’t been eating it in their cage then they cannot go on the lawn for longer than a few minutes for the first several times. You then have to build up by adding in a bit more time (10-15 mins at a time for example) every few days. So you would be looking at perhaps two weeks before they can stay out for an hour.
(If people are telling you an hour is fine for the first time then those piggies should have had grass handpicked for them in their cage for a few weeks (and in quite large amounts) prior to that first time on the lawn.)
Please read this guide as it explains everything.
Fresh Grass and Lawn Time - Tips for Avoiding Spring Time Deaths
This process has to be repeated every spring, or after any extended period without grass in their diet
There are several lawn weeds that they cannot eat - buttercup; daisies and moss are toxic. Any grass which may have been exposed to dog pee (toxic) is also out of bounds.
There is also the temperature to consider. You have to be able to stand with bare feet on the grass for five minutes without feeling cold or damp before the piggies can go out.
