Interpretive Summary: Supplementation of Bacillus subtilis-based probiotic reduces heat stress-related behaviors and inflammatory response in broiler chickens.
By: Jackie Walling
The effects of supplementing a Bacillus subtilis-based probiotic in the diet of broiler chickens during heat stress (HS) was examined in a recent article published in the May 2018 Issue of the Journal of Animal Science. Probiotics are good bacteria in the gut that help control behavior and health. Prior to this study, B. subtilis has been used in broilers under thermo-neutral conditions to inhibit pathogenic proliferation and maintain gut integrity. When broilers are subjected to conditions above the body’s thermo-neutral zone, physiological homeostasis, immunity, and digestion all suffer as a result. Past studies in humans and rodents indicate inflammation and stress-induced behaviors can be reduced by control in the microbiota-gut-brain axis and the microbiota-gut-immunity axis.
A total of 240 1-day-old broiler chicks were selected, divided by body weight into four different temperature-diet treatment groups, and housed in two separate rooms. The four groups were TN-RD (thermoneutral-regulatory diet), TN-PD (thermoneutral-regular diet with Sproulin), HS-RD (heat stress-regular diet), and HS-PD (heat stress-regular diet with Sproulin). Assigned diets started on Day 1 and adjustments were made to accommodate nutritional requirements of the growing chicks. TN temperature started at 34⁰C decreasing by .5⁰ each day until stabilizing at 21⁰C for the duration of the experiment. The HS group began exposure to heat conditions of 32⁰C on Day 15 for a period of 10 hours each day. Daily posture and heat related behaviors were observed for 43 days before sacrificing the birds to collect body weight, blood samples, cecal tonsils, and cecal content.
Behavioral observations showed all HS broilers spending more time panting, wing spreading, and squatting close to the ground to stay cool compared to birds on either diet in TN conditions. Within the HS groups, those on PD exhibited these behaviors less and spent more time standing and walking compared to the RD group. Keeping diets identical and looking at different temperature conditions showed the HS-RD birds spent more time sleeping, sitting, and dozing than the TN-RD group. The TN-PD and HS-PD groups showed little differences in such postures.
Overall, this study has shown B. subtilis to have a beneficial effect on broilers under both TN and HS conditions indicated by improvements in performance, body weight, average daily gain, and feed conversion ratios. It does this by inhibiting bacterial pathogenic reproduction and promoting the utilization of feed through producing a more diverse gut flora. While HS typically reduces digestive enzyme activity causing reduced feed intake, B. subtilis accelerates feed metabolization and leads to an increase in foraging activity of the broilers. HS causes greater negative reactions in stress-related behaviors compared to TN conditions, but HS-PD showed less behavioral problems than HS-RD. The probiotic used during HS produced lower IL-6 levels and higher IL-10 levels than those in the RD group indicating the inflammatory response was more controlled. Under both temperature conditions, spore forming Bacillus were found in cecal content, but higher counts were taken in the broilers provided the probiotic. Many negative effects of HS can be improved with the supplementation of B. subtilis in the diet.
For detailed results, read the full article, “Supplementation of Bacillus subtilis-based probiotic reduces heat stress-related behaviors and inflammatory response in broiler chickens” in the Journal of Animal Science.