This odd numbered long-chain fatty acid is unusual in most biological systems and is therefore often useful as an internal standard.{50561} Heptadecanoic acid is found in trace amounts in the milk of ruminants as it is produced by bacterial flora in the rumen of ruminants.{50562} It can therefore be used as a biomarker of dairy fat intake. Heptadecanoic acid has been used as a comparison to palmitic acid in the study of pheromones because it cannot be converted to the pheromone.{50563}