Effect of diet on plasma tryptophan and serotonin in trained mares and geldings.

The study examined the impact of a high fiber versus high starch diet on plasma serotonin and tryptophan levels in moderately trained Dutch warmblood horses. Results revealed higher serotonin levels and a higher acidic quotient in horses given a high fiber diet, along with higher tryptophan levels observed in mares as compared to geldings.

Methodology

• The research was conducted on 36 Dutch warmblood horses, moderately trained. These horses were divided into two equal groups. One group was fed a high fiber diet (n=18), and the other a high starch diet (n=18).
• The experiment was performed over eight weeks, with the researchers collecting plasma samples from the horses three hours post-feeding when the horses were at rest.
• The sampling period was divided into two time slots – 11:00 hours and 14:00 hours. The aim was to examine if the diet and rest time have any influence on plasma tryptophan (TRP) and serotonin (5-HT) levels.

Key Findings

• The study found that both tryptophan and serotonin levels in plasma were significantly influenced by the type of diet the animal consumed.
• Horses that were on the high fiber diet showed considerably elevated plasma 5-HT and pH levels in comparison to those that consumed a high starch diet. Hence, their blood had more serotonin and was more acidic.
• The findings revealed that mares (female horses) had significantly higher tryptophan levels in comparison to the geldings (castrated male horses).

Significance

• The research paper notes that plasma 5-HT (or serotonin), could serve as an effective marker of serotonergic activity in horses. This indicates that diet, especially a high fiber one, might play a crucial role in influencing serotonin levels.
• The higher levels of tryptophan observed in mares could suggest a gender-based difference in the metabolism or handling of this particular amino acid by the body, which needs further study for confirmation.