PSI-15 Effect of L-tryptophan on aggression, aberrant behaviour and growth in growing pigs

Aberrant behaviours in grower pigs (e.g. tail-biting) have been shown to involve the serotonergic system and along with aggressive behaviours, to result in both significant economic losses and reduce animal welfare. Tryptophan (TRP) acts as a direct precursor to serotonin and so the objective of this study was to determine whether varying inclusion rates of dietary L-tryptophan (TRP) effect aggression, behaviour and growth in grower pigs (n=90). Three feed treatments were examined in a completely randomized block design 1) Control diet (TRP at 100% standard ileal digestible (SID) requirement), 2) TRP at 175% SID requirement and 3) TRP at 250% SID requirement. Each trial (n=2) lasted a total of 29 days, with feed and water being provided ad libitum. Sex, weight and litter origin were balanced across pens in each trial (n = 3 pens/treatment [5 pigs/pen]). All feed was weighed and feed intake measured. Pig weights were recorded weekly. Behaviour was recorded continuously 12 h/d (06:00-18:00), 3 d/wk. An ethogram of 13 mutually exclusive behaviours was used to assess behaviour and all instances of aggression were evaluated for severity and duration of fighting. Body scratch scores, tail lesions and ear lesions were also recorded (d 8, 15, 22 and 29). Plasma and serum samples were taken from 3 pigs/pen (n=27/trial) at four different time points (d 8, 15, 22 and 29) for analysis of TRP and serotonin respectively, using ELISA. Preliminary data analyses indicate no effect of diet on growth (P>0.05) and no differences in behaviour, aggression, or ear- or tail-lesions (P>0.05). ELISA results are forthcoming. Overall, data suggest L-tryptophan does not positively influence growth, behaviour or aggression in grower pigs.