Many back injuries occur when sheep are being handled, especially when lifting sheep over a fence. This is often done to save time, rather than dragging the sheep to a gate, especially if the pen is full.  This method will minimise the risk of injury:

Never try to lift a heavy sheep over a fence on your own.  Get someone to lift the hind legs while you lift its front end.

1. For a small sheep, lift it up backwards, and hold it by the neck and a front leg (Picture 1).
2. Then grab both front legs, lean back to lift the sheep a bit higher, while at the same time using your knee to give it a push-up and over the fence.  Your knee acts as a fulcrum for leverage to help reduce the weight. (Picture 2)

Picture 1 Picture 2