When the lambs get to a certain size they can still put their heads through the sheep fencing but they can’t pull themselves back out.
This is when you loose ear tags, which is why I just have small butcher tags in their ears until I sell them or they grow too big to put their heads through the sheep fence. It is very hard to push the lambs heads back through as they strain their heads upwards against the wire.
I have also had kind neighbors rescue lambs by cutting the fence around their heads. Both of these ways are wrong, one damages and weakens the fence the other is too much hard work.
What you do is catch the lamb by it’s two hind legs pick it up like a wheel barrow and pull backwards. Tipping them forwards lowers their head enough so that when you pull back the lamb just slips out of the fence.
It is very easy and my Ma has even done it and she would prefer to have nothing to do with sheep at the best of times.
This poor fellow had a hard night and was very hungry once I had pulled him free. A short Video of me pulling lamb out of the fence and him happily munching once freed.