Gas Colic with Megaesophagus Senior Horse

PS She gets a carrot with her Equioxx pill in the evening usually around 9pm when we take our dogs out. We typically feed the evening meal between 5 and 6pm. Perhaps her pill should be fed before she gets her senior feed to buffer it?

Nikki was scoped today. They did confirm that she has a mild case of megaesophagus higher up in the esophagus. “She was noted to have dilation of her esophagus at about 140-170cm consistent with megaesophagus.” The Vet did show me where the opening to the intestines also was not opening/closing as tight as it should be.
She had fasted for about 16 hours, so there was nothing in her system. Despite that, there was lots of foaming in the esophagus. So the drooling doesn’t appear to come from food that is blocking the saliva from going down.
She had a mild gas colic 3 weeks ago, so I decided to have her scoped. No ulcers. She was tentative with her slop after the colic for a few days, but she appears to be back to normal.
They showed me where she had some dysfunction while breathing. These folds where the arrows are pointing open and close as she breathes. On one side it doesn’t quite work right; it doesn’t open and close all of the way. She said that this is the “roaring” that I hear when she exercises.

Response from the Fenway Friesian Foundation that is working on the genetics of Friesian Megaesophagus:

Laurie- that’s interesting. I believe this would make only the 3rd or 4th case of megaesophagus I’ve personally seen where the dilation is only in the cervical esophagus (not affecting only the thoracic portion or esophagus).
We see poor motility of the pylorus (the muscle that controls the exit of the stomach) in horses with gastroparesis and we see a fair number of horses that have both megaesophagus and gastroparesis.
The foam in the esophagus we see often too. I believe it is latherin, which is a protein in sweat and it’s also present on saliva in order to help lubricate the saliva during chewing.
Was the larynx paralyzed on only the left side? That is what you’d commonly see with roaring. We are growing curious about the larynx after seeing horses with megaesophagus have bilateral laryngeal paralysis, which is apparently quite rare vs. just having one side paralyzed. We can’t attribute the bilateral paralysis to anything else you’d typically be able to tie it to such as guttural pouch mycosis, EPM, or toxicity from exposure to chemicals like herbicides, pesticides or fertilizers.