Effect of a synbiotic supplement on fear response and selected stress indicators in broiler chickens subjected to cyclic heat stress

Authors: MOHAMMED, AHMED - Purdue University; MURUGESAN, RAJ - Biomin America, Inc; Cheng, Heng-Wei

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2021
Publication Date: 2/7/2021
Citation: Mohammed, A.A., Murugesan, R.G., Cheng, H. 2021. Effect of a synbiotic supplement on fear response and selected stress indicators in broiler chickens subjected to cyclic heat stress. Animals. 11(2),427. https://doi.org/10.3390/ani11020427.
DOI: https://doi.org/10.3390/ani11020427

Interpretive Summary: Dietary supplementation of probiotics and synbiotics have become a useful biotherapeutic method for treating stress-induced mental illness and psychosocial disorders in humans. These supplements have been used for increasing growth and production in broilers. The objective of this study was to investigate if synbiotic supplementations have the similar function to reduce stress-induced fear in broilers subjected to heat stress. Day-old broiler chicks were randomly assigned to 1 of 3 dietary treatments: regular diets mixed with a synbiotic at 0 (control), 0.5 (0.5X), and 1.0 (1.0X) g/kg diet. The results indicate that the synbiotic reduced both novel objective- and isolation-induced fear and related stress hormone release in heat stressed broilers. The findings provide insights for poultry producers and scientists to develop novel management strategies to use synbiotics to increase broiler health and welfare during summer hot conditions.

Technical Abstract: The aim of this study was to evaluate the effect of a dietary synbiotic supplement on fear response and selected stress indicators in broiler chickens subjected to cyclic heat stress (HS). A total of 360 1-d-old Ross 708 broiler chicks were randomly assigned to 1 of 3 dietary treatments (8 replicates per treatment): a regular diet mixed with a synbiotic at 0 (control), 0.5 (0.5X), and 1.0 (1.0X) g/kg. The synbiotic contains a probiotic mixture of 5 microbial strains (Enterococcus faecium, Pediococcus acidilactici, Bifidobacterium animalis, Lactobacillus reuteri, and Lactobacillus salivarius) and a prebiotic (fructooligosaccharides). The broilers were reared under a thermoneutral condition from d 1 to d 14, then stressed at 32° C for 9 h daily until d 42. The touch, novel object, and isolation tests were separately conducted on d 35 (HS for 21 days); and tonic immobility (TI) test was performed on d 41 (HS for 27 days). At d 42 (HS for 28 days), plasma was collected for detecting corticosterone (CORT) and tryptophan concentrations; and duplicated blood smears per broiler were prepared for examining heterophile/lymphocyte (H/L) ratios. Compared to controls, synbiotic fed broilers regardless of concentrations had a short latency to make the first vocalization with a higher vocalization rate during the isolation test (P < 0.05). The H/L ratios were lower in synbiotic fed broilers, particularly in 1.0X group (P < 0.05). In addition, the number of birds to reach the observer during the touch test and plasma concentrations of tryptophan were higher in 1.0X group (P < 0.05). However, there were no treatment effects on novel object test, TI test, and plasma CORT levels (P > 0.05). In conclusion, the current results indicate that the synbiotic may reduce fear and related stress response of broilers subjected to cyclic heat episodes. The data provide new sights for further investigation the effects of synbiotic on broiler health and welfare during heat stress.