US research finds tryptophan eases aggression in pigs

Researchers at Purdue University, West Lafayette, Indiana found that a diet with extra tryptophan reduces aggression at mixing of young pigs.

Aggression can be a major problem for swine production as it negatively impacts pig health and welfare.

Increasing tryptophan (TRP) intake to raise brain serotonin (5-HT)--key for aggression control, and long-term positive social handling can reduce stress in pigs.

In a feed trial, it was found that the TRP-added diet raised blood TRP concentration of three- and six-month-old gilts by 180.7% and 85.2% respectively, reduced behavioural activity and time spent standing, while increasing lying behaviour, mostly in grower gilts.

High-TRP diet reduced the number of agonistic interactions, and aggressiveness in three-month-old gilts, which took longer to attack the intruder pig, and displayed fewer attacks on the first day of testing.

Long-term positive social handling improved growth performance and had a slight effect on behaviour.

Provision of enhanced TRP diet reduced behavioural activity and aggressiveness of grower gilts, and these results are likely mediated by activation of brain serotonergic system.

The scientists concluded that short-term high-TRP dietary supplementation may be used to reduce aggression at mixing in young pigs.