Is Autumn Grass Bad for Sheep?

I have been told by a local farmer that autumn (fall) grass is bad for sheep and that they should be primarily eating hay.  Does anyone know about this?

Depend on a lot of factors...

if the grass is very lush and especially after a frost or heavy freeze, early in the morning, this can cause problems. Hay will help round out the nutritional overdoses you might be dealing with. I wouldn't say that you should be feeding mostly hay per say, but giving it free choice probably wouldn't be a bad plan.

I'm not sure what you mean by this... Are you referring to warm-season grasses like Bermuda grass, or grass that has been stockpiled over winter? Or are you just referring to grass that grows in the fall? If so, I don't think you really have anything to worry about.

I just meant normal meadow grass that stopped growing in the summer due to a drought but whizzed into action the minute we got some rain in the autumn.  The farmer said that spring grass is the highest in nutritional value and that's why you make hay with it.  He says tha autumn grass doesn't have any value - it's just empty calories that fills the sheep up but gives them no benefit.  I have put a big hay bale out under cover in their field and a hay feeder in their house, so free-choice is there.  They still prefer the grass.

I had been giving them some rolled barley morning and evening but he said to stop that to force them to go for the hay.  He says their second choice should be straw, then third choice grass.  But hey, is that natural?

I'm just worried because this is the first time I have had sheep and one died a couple of weeks ago.  She got visibly ill in the moning and died that evening.  And the ram is apparently a bit skinny.  I only had 4 and now I only have 3 

I don't believe it is true that it is devoid of nutrients. It sounds like perhaps your sheep had bloat. Do you have sodium bicarbonate available to them? Have you looked into supplements? Kelp, sea salt and some sort of calcium might be good ideas... a sheep trace mineral as well.

The problem with fall grass as with spring grass is it can be too nutrient rich, too high in nitrogen which causes bloat.

Hmm, I'm not sure, but I don't think it would make much of a difference.

Is the free choice hay in the barn where they sleep? What you do is make sure they have a full belly of high quality hay before they go out to pasture every day, this should minimize risk of bloat. Animals that haven't had high nutrient food and suddenly gain access to high nutrient lush forage are the ones who suffer from bloat. Fall harvested grass for hay can also make excellent feed.