Tryptophan is a precursor to 5-hydroxytryptophan, which is further decarboxylated to form the neurotransmitter serotonin; in the pineal gland serotonin is methylated to form melatonin, which plays a role in regulating diurnal rhythms<ref name="Stipanuk"/>. Supplementation of tryptophan has been evaluated as a behaviour modifying agent in dogs, although results have been inconsistent. One study feeding varied levels of dietary protein with and without tryptophan supplementation found that feeding a lower protein diet supplemented with higher levels of tryptophan may decrease territorial aggression in dogs, but these same dietary changes exerted no affect in dominance aggression or anxiety<ref>DeNapolo JS, et al. Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs. JAVMA 2000; 217:504–508.</ref>. An additional study looking at anxiety in dogs showed no effect with tryptophan supplementation<ref>Bosch G, et al. Dietary tryptophan supplementation in privately owned mildly anxious dogs. Appl Anim Behav Sci 2009;121:197-205.</ref>. | Tryptophan is a precursor to 5-hydroxytryptophan, which is further decarboxylated to form the neurotransmitter serotonin; in the pineal gland serotonin is methylated to form melatonin, which plays a role in regulating diurnal rhythms<ref name="Stipanuk"/>. Supplementation of tryptophan has been evaluated as a behaviour modifying agent in dogs, although results have been inconsistent. One study feeding varied levels of dietary protein with and without tryptophan supplementation found that feeding a lower protein diet supplemented with higher levels of tryptophan may decrease territorial aggression in dogs, but these same dietary changes exerted no affect in dominance aggression or anxiety<ref>DeNapolo JS, et al. Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs. JAVMA 2000; 217:504–508.</ref>. An additional study looking at anxiety in dogs showed no effect with tryptophan supplementation<ref>Bosch G, et al. Dietary tryptophan supplementation in privately owned mildly anxious dogs. Appl Anim Behav Sci 2009;121:197-205.</ref>. |