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 the pigs’ 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.
Objective of this study was to feed a short-term high-TRP diet to grower (3 months) and finisher (6 months) maternal gilts that were either socially handled or not and measure their behavioural activity and aggressiveness.
In a trial 48 gilts were used; half of these were fed a high-TRP diets and the other half a control diet and up to 3 months of age the pigs were ‘social handled’.
At 3 months, two handled and two non-handled pens were assigned to control while the other four pens were assigned to the high-TRP diet fed ad libitum for 7 days. At 6 months of age, pen assignment to dietary treatments was swapped.
Body weights and blood were taken at days 1 (pre-feeding) and 7. Blood samples were analyzed for TRP and 5-HT concentrations.
Behaviour was recorded from days 1 to 5. Aggression evaluation in the home pen focused on counts of agonistic interactions, bites and head-knocks per interaction during.
The TRP-added diet raised blood TRP concentration of 3- and 6-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 3-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.