MicroRNAs (miRNAs) have emerged as one of the most promising classes of minimally invasive biomarkers in animal health. Over the past two decades, research has shown that these small regulatory RNAs are not only remarkably stable in blood and other biofluids, but also closely linked to disease processes. Their potential as biomarkers therefore lies not only in their accessibility, but in their fundamental role in regulating the molecular mechanisms underlying disease.