Proper Sainfoin pasture management help please.

My sainfoin field is 5 years old and very different this year than last. Last year we could lose the dogs in the field if not for their tails sticking up like white flags while they ran. This year it's ankle high and I don't think it's getting taller as it's setting blooms already. There was some discussion on whether the pigs should have unlimited access to the field. They've been grazing it for a month now. They graze sporadically and they don't eat it down to the base, leaving 3-6 inches of the plant untouched. I can tell that many of the plants in bloom were not grazed. It's easy to see where a pig has crunched it. Still, should we be allowing them in it all the time? There are 3 left right now and we have approx 5 acres of sainfoin (planted 4 but it's been spreading).

Is there something we should be doing to help it grow? Is it the weather? Why is it so small this year?

I haven’t grown sainfoin, but have read a fair bit.

My understanding is that most farmers using sunroom will rotate sainfoin field on a 3 to 5 year cycle because the plants get less vigorous just as you describe.

The one just around the corner from me has just been ploughed, making me and my bees very sad :(

That is a scary possibility. Opinion seems fragmented on it. Looking at the University in my state they say a stand can last 3-6 years and in the same paragraph state that the seeds came from a 25 year old stand. We have a rancher friend who has a sainfoin stand they hay. I've got an email out to her to see what they do. It better not die!