Dr. Richard Hopper, extension veterinarian at Mississippi State University, said it is common for cattle to eat acorns, but few are poisoned by them in the state. Most happen when acorns are abundant and pastures offer little forage. Tannins are found not just in acorns, but in oak buds and leaves at certain times. Acorn poisoning upsets the digestive system. The target organ is the kidney, which swells considerably and loses its ability to concentrate urine.
Affected cattle urinate frequently and have a dark diarrhea.
If the condition is advanced, recovery is rare. Blair McKinley, MSU extension cattle specialist, said most cows can eat a few acorns or oak buds without being poisoned. It's when they eat large amounts that a problem occurs. If they like their taste, cattle will go back to acorns even if hay is provided. Giving hay prevents many cattle from foraging for acorns, but the best solution is to move the cattle away from oak trees.