Tryptophan: The link between poultry welfare & nutrition

Tryptophan (Trp) is an essential amino acid (AA), which is the building block of protein, therefore it cannot be synthesized by the body itself and must be obtained through food; it is important for many metabolic functions.

Trp supplementation improves broiler performance through increased body weight gain, reduced feed intake and improved feed efficiency. As a result, the supplementation of this essential amino acid has significant economic impacts on broiler production.

Besides the known requirements of Trp for growth, it also serves as a precursor to neuroendocrine messengers such as serotonin and melatonin, which can impact welfare.

A tryptophan deficiency could affect behavioral responses to stress.  Severe feather pecking, an abnormal behavior in response to a multitude of stressors, is associated with serotonin levels. Trp could therefore play a role in the prevention of this abnormal behavior.

The figure below compares feather pecking genotypes and phenotypes. Both high-pecking genotypes and phenotypes had lower serotonin levels at a younger age in comparison to victims and neutral birds.

Distress negatively affects the health of all animals as their immune system is compromised.

The figure below illustrates the gut–brain axis, which refers to the bidirectional communication between the nervous system and the gut. When chickens experience chronic distress, the intestinal and immune cells transmit signals to the brain. These stimuli activate the hypothalamic–pituitary–adrenal (HPA) axis and increase the blood corticosterone levels. Chronic distress lowers serotonin levels and leads to sickness behavior in chickens.

A study confirmed the hypothesis that Trp enhances intestinal barrier function by regulating mucosal serotonin production in distressed broilers. Serotonin and Melatonin production are inherently linked.

Handling and transport can result in both acute and chronic stress, depending on the scale of the operation and time it takes to catch and process chickens. The size of barns and number of birds are increasing, resulting in longer catching and processing times. Trp supplementation towards the end of the growing or laying period can reduce struggling during handling and in transit. Resulting in improved bird welfare and handler ease, as well as reduced number of dead on arrival (DOA), injuries and improved meat quality.

               1. Control behavioral responses to stress such as feather pecking

               2. Improve coping ability during handling & transport