Effect of a Synbiotic Supplement on Fear Response and Memory Assessment of Broiler Chickens Subjected to Heat Stress
Ahmed Mohammed | Manal Mahmoud | Raj Murugesan | Heng-wei Cheng
The aim of this study was to evaluate the effect of a synbiotic containing a probiotic (<i>Enterococcus faecium</i>, <i>Pediococcus acidilactici</i>, <i>Bifidobacterium animalis</i>, and <i>Lactobacillus reuteri</i>) and a prebiotic (fructooligosaccharides) on fear response, memory assessment, and selected stress indicators in broilers subjected to heat stress. A total of 360 1-day-old Ross 708 chicks were evenly divided among three treatments: a basal diet mixed with a synbiotic at 0 (G-C), 0.5 (G-0.5X), and 1.0 (G-1.0X) g/kg. After 15 d, the broilers were exposed to 32 °C for 9 h daily until 42 d. The object memory test was conducted at 15 day; touch, novel object, and isolation tests were conducted at 35 day; tonic immobility (TI) took place at 41 day. At 42 day, plasma corticosterone and tryptophan concentrations and heterophile/lymphocyte (H/L) ratios were measured. Compared to controls, synbiotic-fed broilers, regardless of concentration, had a shorter latency to make the first vocalization, with higher vocalization rates during the isolation test (<i>p</i> = 0.001). the G-1.0 group had the lowest H/L ratio (<i>p</i> = 0.001), but higher plasma tryptophan concentrations and a greater number of birds could reach the observer during the touch test (<i>p</i> = 0.001 and 0.043, respectively). The current results indicate that the synbiotic can be used as a growth promoter to reduce the fear response and stress state of heat-stressed broilers.
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