The effect of different levels of dietary threonine on performance, carcass characteristics, immune system and blood factors of Japanese quail under heat stress

The present experiment was performed to compare the effect of different levels of dietary threonine on performance, carcass characteristics and immune system and blood factors in Japanese quailunder heat stress. For the experiment, 300 one-day-old Japanese quail chicks (Coturnix coturnix japonica) were used in a completely randomized design with six levels of threonine in 6 treatments and 5 replications, each replication containing 10 chicks. The percentages of threonine in the diet of the experimental treatments were: 1) 0.82 %, 2) 0.92 %, 3) 1.02 %, 4) 1.12 %, 5) 1.22 % and 6) 1.32 %. The results showed that the increase in body weight and feed conversion ratio improved significantly in treatments 5 and 6 (p < 0.001). Levels of 1.12 and 1.22% of threonine in the diet had a significant effect on carcass percentage (p < 0.001). There was no significant difference in the weight of lymphatic organs and the titer of antibodies produced against SRBC (sheep red blood cells) in the treatments (p>0.05). Dietary threonine levels had a significant effect on serum uric acid, HDL (high-density lipoprotein) and LDL (low-density lipoprotein) concentrations (p < 0.05). Liver enzyme levels were not significantly different in any of the treatments (p < 0.05). The results showed that increasing threonine in quail diet up to 1.22% can have beneficial effects on performance and improvement of carcass characteristics under heat stress conditions.