frosty grass and loose droppings

[dressage-diva]

hi there,

my 18yr old mare has been passing loose and watery droppings these past few days.
she's not eating as much of her haylage and not drinking as much as usual.
She has a hard feed morning and night which she eats happily and she's well in herself.

I can only assume that the frosty grass we've had these past few days is causing the problem,

obviously if she doesn't improve soon i shall call the vet.

is anyone else's horse having this problem and what can i do to help her?

Thanks