New research suggests that probiotics can help protect broilers against gut diseases, such as necrotic enteritis. Increasingly, probiotics serve as a substitute for antibiotic growth promotants, which are no longer used.
“The removal of antibiotics comes with some consequences, including impaired growth and increased susceptibility to infection,” reported Mohammed Alizadeh, PhD, University of Guelph. “Probiotics are an alternative, given their immunoactivity.”
Alizadeh conducted several studies to better understand how to use probiotics for top performance in broilers. He discussed his research in a webinar hosted by Canadian Poultry.
Lactobacillus ‘golden’ species tested in ovo
The aim of the first study in Alizadeh’s research was to identify Lactobacillus species to include in a probiotic cocktail. Lab testing on immune activity identified five species for the cocktail: L. salivarius-26, L. johnsonii-39, L. reuten-42, L. crispatus-44 and L. gasseri-49.
Next, the probiotic cocktail was tested in ovo. “Early establishment of beneficial bacteria is very important,” Alizadeh explained. “Colonization of the chicken intestine by commensal bacteria is an ongoing process that begins immediately after hatch and can be established within 2 weeks post-hatch.”
Testing involved two doses of the Lactobacillus probiotic: 106 colony-forming units (CFU) and 107 CFU. Each dosage level was injected into a set of 40 embryonic eggs on in ovo day 18. A third group of 40 embryonic eggs was only immunized. A fourth group of eggs — the control group — was not injected or immunized.
The researchers collected blood samples from all birds on days 14, 21, 28 and 35 for analysis.
The results demonstrated that the highest dose of Lactobacillus at 107 CFU elicited the best response for stronger cell- and antibody-mediated responses. Administering the probiotic in ovo “modulated lymphocyte populations in the spleen of chickens, suggesting their potential role in lymphoid organ development and contribution to early protection in hatchings,” Alizadeh said.
Testing control of necrotic enteritis
Next, Alizadeh assessed the ability of probiotics to control necrotic enteritis, a major poultry disease caused by Clostridium perfringens.
First, he conducted in vitro screening of the Lactobacillus probiotic cocktail and measured the antibacterial activity against C. perfringens. Based on screening responses, Alizadeh chose the Lactobacillus cocktail 107 CFU and 108 CFU for the second study.
“It is very important with probiotics that appropriate doses are selected for optimum results,” Alizadeh explained. “Probiotics should pass through the stomach and reach the intestine to colonize the gut. If the dose is too low, the probiotics could flush out in the feces and not stimulate the immune response, making them ineffective.
“On the other hand, high doses of probiotics can also cause gut problems, resulting in significant microbiota disruption, immune system overactivation, nutrient competition with the host, excessive metabolite production and excess mucus production,” he added.
Four groups of chickens were used in the study. One group received doses of the 107 CFU probiotic cocktail on days 1, 7, 14 and 20. Another group received the 108 CFU cocktail on the same days. Both were challenged with C. perfringens on days 22 to 24. A positive-control group was also challenged with C. perfringens, while a negative-control group was not challenged.
The morphology results and lesion scoring revealed that the higher level of probiotics (108 CFU) provided greater protection and resulted in a greater reduction in lesion scores compared to 107 CFU.
“The findings indicate that Lactobacillus can be used to mitigate necrotic enteritis by modulating intestinal immune responses and improving and maintaining intestinal morphology,” Alizadeh explained.
Probiotic performance under stress
The Lactobacillus cocktail underwent a stress test to determine the effects of probiotics on performance and gut health in stressed birds.
“For the test, we chose high stocking density because it can impact the immune response of the jejunum and make it more susceptible,” Alizadeh said. “It also impacts more droppings per area for higher C. perfringens exposure, along with poor litter quality that promotes coccidiosis.”
Two pens were populated with a 15 birds/m2 density, 44 birds in each pen. One group received the probiotic cocktail and the other did not. Another two pens were populated with a 30 birds/m2 density, 88 birds in each pen. One group received the probiotic cocktail and the other did not.
All birds were inoculated with the cocktail on days 1, 7, 14 and 20. The research team took bodyweight on day 21. They also examined the ileum, cecal tonsils and cecal contents and performed lesion scoring.
“The probiotics mitigated the development of necrotic enteritis in chickens raised under high stocking-density conditions,” Alizadeh said. “Probiotics also improved overall performance by increasing bodyweight gain.
“They also decreased intestinal inflammation by reducing the expression of inflammatory cytokines in the ileum, contributing to immune homeostasis,” he continued. “In addition, the probiotics enhanced gut microbial alpha diversity.”
Mitigating Salmonella shedding?
The last study Alizadeh conducted was measuring the antimicrobial activity of different Lactobacillus species against Salmonella. In vitro screening identified six Lactobacillus species candidates: L. salivarius-26, L. reuteri-42, L. salivarius-43, L. crispatus-44, L. salivarius-46 and L. gasseri-49.
Chicks in the treatment group were inoculated with the Lactobacillus probiotics on day 1 and challenged with S. Typhimurium on day 2. A positive-control group was not treated but was challenged. A negative-control group was neither treated nor challenged. All birds were examined on day 5 post-infection.
The results were positive for reducing Salmonella. “The Lactobacilli cocktail containing six species of a concentration of 107 CFU reduced Salmonella shedding by 1 log unit,” Alizadeh said.
“However, achieving effective control of Salmonella at the farm level will require a comprehensive approach including vaccination, feed additives and strict biosecurity measures,” he concluded.
