Presence of salicylic acid in standardbred horse urine and plasma after various feed and drug administrations.

This research investigates how the levels of salicylic acid in the urine and blood plasma of Standardbred mares change after being fed different types of feed and administered various drugs orally and topically.

Study Design and Procedure

• This study was conducted on Standardbred mares to observe the changes in the salicylic acid levels in their plasma and urine after they were given different types of hay in their feed.
• To further understand the effects of salicylic acid and related compounds, the horses were also administered two drugs: acetylsalicylic acid orally and methyl salicylate topically.

Findings

• The study found that salicylic acid levels went up in the urine and plasma of those horses that were fed lucerne hay.
• It was also seen that there was a pattern to the plasma and urine elimination of salicylic acid that depended on the type of feed and the feeding schedule. This pattern followed a diurnal, or daily, cycle.
• When the horses were administered oral acetylsalicylic acid, their plasma and urine salicylic acid levels matched with the levels noticed after feeding them lucerne hay, within 24 hours.
• The study noted that the elimination of salicylic acid was both quick and complete, with the acid having a half-life between 5 and 7 hours.
• The topical administration of a larger dose of methyl salicylate (8.4 g) resulted in higher urinary salicylic acid levels for up to 6 hours after application. However, a smaller dose of the same (3.4 g) did not cause plasma or urine salicylic acid levels to rise above the levels observed following administration of lucerne hay.

Implications

• This research gives insight into how a horse’s diet can impact the diagnostic markers used in checking for drug usage. As some types of hay result in increased salicylic acid levels, this could potentially affect drug testing results.
• The administration of certain drugs, like acetylsalicylic acid and methyl salicylate, can also influence these levels and should be considered when interpreting drug testing results in horses.