Adding supplemental tryptophan to diet can calm pigs
The researchers gave 3-month-old grower pigs and 6-month-old finisher pigs 2.5 times the normal amount of tryptophan in their diets for one week. This increased tryptophan concentrations in the grower pigs by 180 percent and in the finisher pigs by 85 percent.
The researchers compared the pigs' behavioral activity and aggressiveness before and after seven days of the tryptophan-supplemented diet, as well as with a control group that did not receive the diet supplementation. To test aggressiveness, an intruder pig was placed in a pen with the experimental and control pigs, and the researchers observed how long it would take for the pigs to show aggression, up to a maximum of five minutes. The pigs that received the diet supplemented with tryptophan showed less aggression toward the intruder pig than did the control group that didn't receive the extra tryptophan.
The introduction of new pigs into a group can throw off the hierarchy that pigs naturally establish, resulting in aggression. Thus, the use of tryptophan may help prevent some of this stress and its adverse effects, including poorer welfare, increased disease susceptibility and reduced growth and efficiency.