Journal of Experimental Agriculture International

This study was designed to determine the influence of dietary L-threonine supplementation above the NRC (1994)-recommended level on growth performance, blood profile, antioxidant capacity, gut morphology, and intestinal microbiota in broiler chickens during the starter and grower phases. In a 28-day feeding trial, one hundred and sixty (160) one-day-old Arbor Acres chicks were allotted to four dietary treatments, with five replicates of eight birds each, in a completely randomised design. Treatment 1 received the basal diet without L-threonine supplementation (control), whereas Treatments 2, 3, and 4 received the basal diet supplemented with L-threonine at levels 10%, 20%, and 30% above the NRC recommendation, respectively. On days 14 and 28, blood samples were analysed for haematological, serum biochemical, and antioxidant parameters. Furthermore, birds were slaughtered for gut morphological measurements and microbial-load determination following standard practices. Data were analysed using descriptive statistics and ANOVA at P = .05. During the starter phase, birds fed the diet containing 30% above-NRC threonine had higher total protein (40.24 g/L) and creatinine (88.01 µmol/L) concentrations than birds in the other treatments. During the grower phase, birds fed the diet containing 30% above-NRC threonine had a higher red blood cell count (2.45 × 10⁶/µL) than birds in the other treatment groups. Birds fed the diet containing 10% above-NRC threonine had higher superoxide dismutase activity during both the starter (1.11 U/mL) and grower (1.01 U/mL) phases than birds in the other treatments. During the grower phase, birds fed the diet containing 10% above-NRC threonine had a higher villus-height-to-crypt-depth ratio (8.11) than birds in the other groups, although the value was similar to that of birds fed the control diet (6.46). Birds fed the diet containing 20% above-NRC threonine had a lower total bacterial count (4.30 CFU/g) during the starter phase and a lower Escherichia coli count (2.36 CFU/g) during the grower phase than birds in the other treatments. In conclusion, L-threonine supplementation improved immune function, antioxidant defence, gut integrity, and microbial load without improving growth performance.