[aqh88]

Grass has a higher water content so they have to eat more to get the same amounts of everything as hay but that's actually better. The increased water intake makes things move better and dehydration less likely than hay. Less concern about them having to hit the water bottle as frequently. I forget the exact amount for horses but I believe it's at least 25% more pounds of grass needed to equal the same amount of hay due to the weight of water. Other than that grass has the same nutritional values as hay plus some vitamins like C and E. I would think if anything the fiber would break down some when you dry the grass into hay. You don't add any nutritional value to grass when you dry it. You only lose water and some nutrients.

The only thing I can think of that would make a difference is the age of the grass. Hay is made from older grass that is allowed to grow. New growth in the spring is sweeter with a higher water content and probably slightly less fiber. The fiber still isn't the issue though it's the water and sugar that leads to more problems, usually only diarhea in pigs, than if they overeat on older grass. Generally with grazing animals grass intake should be restricted more on new spring grass or the new growth that comes after cool weather and thunderstorms. Older grass is slightly healthier despite the fact animals prefer to hunt down the newer, softer shoots.