Tamara,

Even the equine endocrinology group, university based, no longer recommends fasting for insulin testing https://sites.tufts.edu/equineendogroup/files/2020/09/200592_EMS_Recommendations_Bro-FINAL.pdf but you should feed nothing but hay.

 Fasting can also affect ACTH readings https://pubmed.ncbi.nlm.nih.gov/24906932/ - lowers it significantly.
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Eleanor in PA

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