LAUSR

Abstract This experiment was conducted to investigate effects of in ovo injecting arginine (Arg), threonine (Thr) and Arg + Thr on humoral immunity, serum differential leukocyte counts and serum biochemical attributes in broiler chickens. Four hundred fertile eggs were randomly assigned to five experimental treatments including: control (none injected), sham (0.5 ml of 0.5% saline), Arg (35 mg/egg), Thr (25 mg/egg) and Arg + Thr (35 + 25 mg/egg) which injected in the amniotic fluid on day 14 of incubation. After hatching, broiler chicks were fed a commercial corn–soya bean diet up to 42 days of age. Broilers received Arg and Thr had higher body weight (p < .05) and daily feed intake (p < .05) than those supplemented with control or sham. Antibody titre against sheep red blood cells increased in broilers in ovo supplemented with amino acids compared to the birds in control group (p < .05) while no beneficial effect of applied treatments observed on the antibody titre against influenza and Newcastle disease viruses. Moreover, in ovo injection of Arg significantly increased spleen and bursa of Fabricius relative weights compared to sham on day 11 of age (p < .05). In ovo administration of Thr resulted in higher serum glucose concentration than the other groups (p < .05). Furthermore, serum albumin concentration increased in response to Thr administration compared to chickens in control group (p < .05). In conclusion, Arg and Thr in ovo supplementation improved humoral immunity of broilers and increased proportional weight of their lymphoid organs in post-hatch period. Highlights In ovo injection of amino acids may improve immune responses in broiler chickens. Supplementation of amino acids during embryonic stage could increase growth performance of chickens. Meet the nutrient requirement of broiler embryo is important for its later growth and immunity.