“Hay belly” refers to distention of the abdomen. When viewed from the front, the horse looks pregnant. However, it is not caused by hay per se. A horse can eat very large amounts of hay and still look trim.
It’s caused by poor fermentation. The distention is from excessive fluid and gas. The usual cause of this is poor quality hay with excessive amounts of cellulose and lignin. These hays are overly mature and border on straw. Stems are thick and woody and/or large amount of stem compared to leaf. Hays should be pliable, with high ratio of leaf to stem.
Another cause is disruption of the microorganisms in the bowel. This often accompanies poor quality hay because there is not enough fermentable material to support good populations of organisms. A change to a better hay usually solves the problem. If not, direct fed microbials (probiotics) can help.
-By Dr. Eleanor Kellon, VMD and Staff Veterinary Specialist for Uckele Health & Nutrition