When are traditional starchy grains like oats and corn generally considered unnecessary or actively harmful for a mule?

Answer

For the average leisure mule ridden only occasionally.

For mules engaged in light work, traditional high-starch grains are often unnecessary and can contribute to calorie surplus and metabolic issues.

When are traditional starchy grains like oats and corn generally considered unnecessary or actively harmful for a mule?
fooddietanimalnutritionmule