Serotonin is a neurotransmitter that helps regulate many body functions, including mood and appetite, metabolism, and blood flow. Serotonin is produced from the amino acid tryptophan, but this pathway is limited, only a small portion of tryptophan normally enters. One way to increase serotonin production is by providing 5-hydroxytryptophan (5-HTP), the direct precursor to serotonin. However, it is not known whether 5-HTP can be effectively supplied through the rumen of adult cattle or whether it can influence blood flow. This study evaluated how delivering 5-HTP into the rumen or the abomasum affected serotonin levels and blood flow in growing beef steers. Five ruminally cannulated steers received water, abomasal 5-HTP, or increasing doses of ruminal 5-HTP. Blood samples were collected to measure serotonin and related compounds, and blood flow in the tail artery was measured using ultrasound. Feed intake and indicators of nutrient metabolism were not affected by 5-HTP. Abomasal delivery increased circulating serotonin, as expected. Importantly, ruminal delivery of 5-HTP increased serotonin in a dose-dependent manner, suggesting that some 5-HTP escaped ruminal breakdown. The highest ruminal dose increased artery size relative to baseline, indicating improved blood vessel dilation. These findings demonstrate that ruminal 5-HTP supplementation can increase serotonin and enhance peripheral blood flow, providing new insight into how serotonin metabolism can be manipulated in cattle.

Read the full article in the Journal of Animal Science.