Acid Reflux in horses

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Took my old retired race horse to the vet last night with symptoms of colic and he had a white foam coming from his mouth and he kept gulping. First think you think is colic, right? Well, he has acid reflux. Horse prilosec is $200 for 40 days. Have any of you experienced this? Vet says it is not real common and the only reason she could diagnose so quickly is because she had a horse with it ages ago. Does anyone else have any experience with this? Any idea of a less expensive way to treat? All ideas are welcome.