Abstract
Tryptophan plays a crucial role in the regulation of aggressive behavior during stressful situations. In this study, we aim to evaluate the effects of different levels of tryptophan supplementation in the feed of weaning pigs and lactating sows. In experiment 1, a total of 144 weaning pigs (Landrace × Yorkshire × Duroc) with initial mean body weight of 6.63 ± 0.21 kg were allotted to three treatment groups with six replicates per group of eight pigs per replicate in a completely randomized design. The treatments included a control group (CW), TW6 (0.06% tryptophan + basal diet), and TW12 (0.12% tryptophan + basal diet). In experiment 2, a total of 40 lactating sows (Landrace × Yorkshire) were allotted to four treatment groups with ten replicates per group of one pig per replicate in a completely randomized design. The treatments included a control (CL) group, TL3 (0.03% tryptophan + basal diet), TL6 (0.06% tryptophan + basal diet), and TL9 (0.09% tryptophan + basal diet). The results of experiment 1 indicated the TW12 group had significantly higher (p < 0.05) average daily gain and feed efficiency than the CW group. Lying behavior increased in the TW6 and TW12 groups, while ear-biting behavior decreased (p < 0.05) in the TW12 group compared to the CW. In experiment 2, During lactation, TL3 and TL6 groups showed significantly reduced (p < 0.05) backfat loss compared to CL. Average daily feed intake improved with tryptophan, with TL6 significantly higher (p < 0.05) than CL. Additionally, lying behavior increased and stereotypic behavior decreased (p < 0.05) significantly. Overall, it can be concluded that the addition of tryptophan in feed can reduce aggressive behaviors, improve skin lesions, and enhance growth performance in weaning piglets. Also, the addition of tryptophan in feed can reduce stereotypic behaviors, and improve feed intake in lactating sows.