From what I heard, the grass was available to be delivered upon request so that the farm doesn't just get a mountain of it all at once like in the funny artwork. The grass would just go bad anyway if that happened.
So as long as the organization's distribution system allows the farm to keep requesting it (I can't imagine why not since the donated amount was reserved for them anyway as Haru Urara's caretakers) then the farm can probably keep requesting it for the other animals there. I personally hope that's the case. While it's difficult to tell what an actual horse would think, the little pink sunshine would definitely want the friends she made to have her treats.
Horses are very social animals, so I imagine the real Urara would be just as happy to know that her hard work was ensuring her 'herd' was going to be taken care of for a very long time.
