Changes

==Roles in the Body==

==Roles in the Body==

NAD and NADP are formed during the degradation of tryptophan in both dogs and cats, though the major dietary precursor of NAD and NADP in both species is niacin (i.e., vitamin B3)<ref name="Ikeda">Ikeda M, et al. Studies on the biosynthesis of nicotinamide adenine dinucleotide. II. A role of picolinic carboxylase in the biosynthesis of nicotinamide adenine dinucleotide from tryptophan in mammals. J Biol Chem 1965;240:1395-1401.</ref>. Increased intake of tryptophan is able to lower the dietary requirement of niacin in dogs<ref>Singal SA, et al. The role of tryptophan in the nutrition of dogs on a nicotinic acid deficient diet. J Biol Chem 1948;176:1051-1062.</ref>, but cats have a much lower production of NAD/NADP from tryptophan relative to dogs and tryptophan intake has very little impact on cat niacin requirements<ref name="Ikeda"/><ref>Da Silva, AC, et al. The domestic cat as a laboratory animal for experimental nutrition studies. III. Niacin requirement and tryptophan metabolism. J Nutr 1952;46:399-409.</ref>. Neither dogs nor cats are able to produce sufficient amounts of NAD/NADP from tryptophan metabolism and a source of dietary niacin is still required by both species.  

NAD and NADP are formed during the degradation of tryptophan in both dogs and cats, though the major dietary precursor of NAD and NADP in both species is niacin (i.e., vitamin B3)<ref name="Ikeda">Ikeda M, et al. Studies on the biosynthesis of nicotinamide adenine dinucleotide. II. A role of picolinic carboxylase in the biosynthesis of nicotinamide adenine dinucleotide from tryptophan in mammals. J Biol Chem 1965;240:1395-1401.</ref>. Increased intake of tryptophan is able to lower the dietary requirement of niacin in dogs<ref>Singal SA, et al. The role of tryptophan in the nutrition of dogs on a nicotinic acid deficient diet. J Biol Chem 1948;176:1051-1062.</ref>, but cats have a much lower production of NAD/NADP from tryptophan relative to dogs and tryptophan intake has very little impact on cat niacin requirements<ref name="Ikeda"/><ref>Da Silva, AC, et al. The domestic cat as a laboratory animal for experimental nutrition studies. III. Niacin requirement and tryptophan metabolism. J Nutr 1952;46:399-409.</ref>. Neither dogs nor cats are able to produce sufficient amounts of NAD/NADP from tryptophan metabolism and a source of dietary niacin is still required by both species.  

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>.

Tryptophan supplementation has also been shown to cause a transient increase in food intake in dogs<ref>Fragua V, et al. Preliminary study: voluntary intake in dogs during tryptophan supplementation. B J Nutr 2011;106:S162-S165.</ref>.

Tryptophan supplementation has also been shown to cause a transient increase in food intake in dogs<ref>Fragua V, et al. Preliminary study: voluntary intake in dogs during tryptophan supplementation. B J Nutr 2011;106:S162-S165.</ref>.