Of sheep; overturned.
A heavily pregnant, broad backed ewe may roll over and be unable to right herself. She is rigwelted.
There is also a beer called Rigwelter due to the similar effect it is said to have on humans.
Riggwelter Ale takes its name from a local Yorkshire Dales farming term which has Old Norse roots; “rygg” meaning back, and “velte” meaning to overturn. A sheep is said to be rigged or “rigwelted”, when it has rolled onto its back and is unable to get back up without assistance.
It seemed the perfect name for a strong beer from the Black Sheep Brewery in Yorkshire.