Poisoning your sheep - how not to do it!

How to grow pasture and feed sheep varies widely across the country. 'What not to do' applies everywhere. Some people have horror stories of poisoning a flock, while others will tell you that sheep will eat anything. Which is right?
It helps to understand a bit about sheep digestion. Sheep's first stomach, the rumen, contains a whole range of bacteria called gut flora, which break down what the sheep swallows. The sheep regurgitates and "chews the cud" to help break it down further, before sending the food through the rest of the digestive system. In the rumen, the perfect gut flora for the sheep's current diet breed up to high levels, and the other gut flora stay in the background. When the diet changes, new gut flora breed up and the previous ones take a back seat. If the diet changes too quickly, before the rumen has time to breed up the new gut flora, the sheep can't digest what it eats. Result - catastrophe! The sheep needs new food to be introduced slowly, so the new gut flora can breed up. The old gut flora digest the old feed while it is being phased out.
A quick change in diet causes problems, especially if it's a big change. If sheep go from dry grass to a paddock of green feed, catastrophe! Bloat, death! If sheep go from green grass to as much grain as they can eat, catastrophe! Acidosis, death!
There is lots of information on the Internet about all these things, but here are some basics about how to introduce new feed slowly.
To introduce green feed, cut some green stuff and feed it out in the dry paddock for a few days. Put some dry feed in the green paddock when you finally move the sheep.
To introduce grain, trail it out along the ground, perhaps in several places, so that the pushiest sheep can't guts too much. Build up the quantity of grain day by day, and start the process again if you change grain types.
For a change to a new paddock with different pasture, move the sheep late in the afternoon when they have a full stomach from the day's feed, so that they eat just a little of the new feed on the first night.

As well as needing slow changes in feed, sheep do better with some variety. Even excellent pasture can be a problem if it is the sole feed. Phalaris can produce "phalaris staggers", clover can produce bloat, brassicas (the turnip family) can kill too. Sheep can safely eat a little bit of most "poisonous" plants, but too much will cause problems. A paddock of potato weed or fat hen is a problem, a few plants are not. If you think too much of one thing might be a problem, one strategy is let the sheep into a "run-off" paddock part-way through each day so they can access hay or something else easy to digest.
When you change paddocks, check the water. Evaporation through a couple of heat waves can raise salinity to dangerous levels, so you may need to drain the trough and refill it.
Problems always come if sheep on dry feed break into lush green feed which is poisonous. There's the tragic story about the make-shift fence around a new windbreak planting of sugar gum. The sheep get bored, push the fence down, and eat all the fresh green poisonous juvenile sugar gum leaves. Or a branch breaks off the oleander tree and lands in the paddock. Yes, you guessed it - catastrophe, death! On the other hand, if they get into your garden and eat all the rose bushes, it's only a catastrophe for the keen gardener.
If anyone tries to tell you that sheep have an instinct to eat the right food, just laugh. However after all these tales of woe, it's useful to know that sheep are tough creatures. It's true that "if you have livestock, you'll have dead stock". But if you have a bit of common sense and not too much bad luck, it's surprising how well sheep cope.