Dear Bob,

Donkeys evolved on very poor-quality forage and browsing plants. Consequently, they do quite well on low-energy forage and can easily overeat on a pasture that might be ideal for horses.  

A few weeks ago, I was at the Donkey Sanctuary in Ireland. They limit their donkey's grass intake by strip grazing and supplement their grazing with barley straw to keep the total caloric intake (digestible energy) down.  

While much emphasis is placed on sugar in feeds, the combination of sugar and starches, which are easily digestible in both forage and grains, can cause problems with some equid—more complex carbohydrates in high-fiber feeds that are digested primarily in the hindgut suit easy keepers much better. Donkeys, ponies, and some light breeds like Arabians and Morgans may fall into the easy keeper categories.  

I recommend working with your vet to determine your donkey's body condition score and ensure it isn't overweight—obesity can directly lead to laminitis in equid. You will most likely need to restrict your donkey's pasture intake and supplement with a high-quality straw or very coarse/mature grass hay to reduce the amount of sugar and starch in your donkey's diet. You may also want to supplement your donkey with a good vitamin/mineral supplement to ensure your donkey receives a well-balanced diet. And, of course, the donkey will need access to clean, fresh water and shelter from rain and wet snow.  

The following link will provide a donkey body condition score sheet:  https://www.thedonkeysanctuary.org.uk/sites/default/files/2018-10/body-scoring-chart.pdf

In addition, the Donkey Sanctuary provides excellent fact sheets that you may find helpful, including information on feeding, laminitis, and weight:  https://www.thedonkeysanctuary.ie/donkey-welfare/care-and-advice

Regarding your horses, hoof rings can signify diet change or fevers. Horses that go from hay to pasture will be more prone to developing seasonal hoof rings. Our cool season grasses in Michigan typically have higher amounts of sugar than grass grown in the Southern states. However, laminitis in horses is observed across the U.S. and in Canada. Keeping your horse on a high forage (of moderate quality) and low starch/sugar diet (usually found in grain products) and managing their weight to be at the moderate body condition score, along with exercise, are all keys to preventing laminitis.  

For an overview of pasture laminitis, please refer to the following article: https://extension.oregonstate.edu/catalog/pub/em-9354-horse-owners-guide-pasture-associated-laminitis#:~:text=Laminitis%20is%20the%20inflammation%20of,which%20are%20starches%20and%20sugars.

Best of luck with your donkey - they are truly special!