Effects of acidified drinking water on performance, carcass, immune response, jejunum morphology, and microbiota activity of broiler chickens fed diets containing graded levels of threonine

• Acidified drinking water improved weight gain in broilers at starter phase.
• Heterophil counts and H/L ratio were increased in broilers fed 110% threonine.
• The villus width and crypt depth were greater in broilers received acidified drinking water.
• The population of E. coli was decreased while Lactobacilli population was increased in broilers received acidified drinking water.

A 2×4 factorial arrangement of treatments was used to investigate the effects of 2 levels of an acidifier supplement (0 or 350 mL/1000 L) in drinking water on growth performance, carcass, immune response, intestinal microbial flora, and jejunum morphology of broiler chickens fed diets based on 4 levels of dietary Thr (100, 110, 120, and 130% of the requirements). A total of 320 broiler chickens were assigned to 8 treatments with 4 replicate pens of 10 broiler chickens per pen. Growth performance traits, including daily weight gain, feed intake, and feed conversion ratio (FCR), were recorded. The broiler chickens immunized against Newcastle disease virus (NDV) at 8 d of age. Blood samples were drawn from the wing vein 7 and 14 d after vaccination for the determination of primary and secondary antibody responses. In addition, blood samples were collected in tubes containing anticoagulant to determine the number of heterophil (H) and lymphocyte (L). At the end of the experiment, 4 broiler chickens per treatment were selected and killed, and, then, the relative weights of carcass parts, jejunum morphology, and intestinal microbial population were determined. The results showed that broiler chickens received acidified drinking water (ADW) had greater (P<0.05) feed intake (28.51 vs. 27.30 g/chicken/d) and weight gain (20.01 vs. 19.26 g/chicken/d) than those received without water additive during the starter period. Neither Thr nor ADW had any effect on any carcass traits of broiler chickens. Heterophil count and H to L ratio were increased (35.87 and 0.63%, respectively) and lymphocyte count was decreased (56.50%) in broiler chickens fed diets containing 110% threonine (P<0.05). However, antibody titer against NDV was not influenced by experimental treatments. In the jejunum, the villus width (136.8 µm) and crypt depth (188.9 µm) were greater and the ratio of VH to CD was lower (6.50) in broiler chickens received ADW (P<0.05). Moreover, the population of Escherichia coli decreased (5.79 vs. 6.23 log10 cfu/g) in broiler chickens received ADW, while lactobacilli population increased (7.45 vs. 6.90 log10 cfu/g; P<0.05). However, dietary Thr had no effect on jejunum morphology and intestinal microbial population of broiler chickens. The present findings indicate that ADW improves growth performance (0–10 d), jejunum morphology, and intestinal lactobacilli population of broiler chickens. In addition, the use of 110% Thr increased H to L ratio in broiler chickens. However, different graded concentrations of Thr did not alter growth performance, intestinal morphology, and microbiota activity.