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were collected from multiple gut sections of representative birds, stabilised on-site for preservation of microbial DNA, and assessed for the presence and quantity of relevant microbial virulence genes by quantitative PCR. Analysis of this data uncovered significant differences in the clusters of E. coli and C. perfringens virulence genes present in the caeca of healthy, undersized, and sick birds, as well as similar trends in food safety-related organisms including Campylobacter and Salmonella. The survey included 77 farms from 18 broiler production complexes in 12 states and sampled undersized birds from healthy flocks, sick birds from high-mortality flocks, and healthy, high-performing birds from all flocks. Clostridial disease was the most frequently reported health challenge in high-mortality flocks. In total, caecal swabs from 571 birds ranging from 1 to 42 days of age were used for analysis of bacterial virulence genes. Avian pathogenic E. coli (APEC) carrying a specific set of virulence genes associated with extraintestinal infection and tissue damage in birds predominated in sick birds from high-mortality flocks. Small, underperforming birds in healthy flocks carried significantly higher levels of non-APEC E. coli with a different set of intestinal virulence factors (eaeA and EAST1) involved in attachment, tissue damage, and aggregation on the intestinal wall (Figure 1).


Microbial population in health-challenged birds Similar trends were seen with other species involved in broiler health or food safety concerns. C. perfringens and its necrotic enteritis-associated toxin gene netB were significantly elevated in sick birds from high-mortality flocks, where necrotic enteritis or other clostridial disease was the most frequent concern. Secondary C. perfringens virulence genes associated with disease in other monogastrics were found very rarely in the survey but were also significantly elevated in sick birds in high-mortality flocks. C. septicum, a cause of gangrenous dermatitis and other myonecrotic infections, was also significantly elevated in sick birds from high-mortality flocks. Neither C. perfringens nor C. septicum differed between healthy birds and small, underperforming birds, suggesting a more limited role in subclinical performance drag than the association seen with non-APEC, toxigenic E. coli. Carriage of microorganisms involved in food safety, such as Campylobacter and Salmonella, was also increased in the dysbiotic gut. Total Campylobacter and C. jejuni were significantly more common in the caeca of sick birds than in undersized birds from healthy flocks (Figure 2). Salmonella was detected at much lower levels than Campylobacter in the flocks surveyed, but carriage trended slightly higher in birds with compromised health. More than one microbial population was often elevated in health-challenged birds, reflecting a broader dysbiosis allowing opportunistic overgrowth by multiple organisms.


Guide for producers Microbial surveillance programmes may guide the decisions of individual producers, particularly in the area of feed additives. Findings may aid in the selection of an effective direct-fed microbial product, prioritising products that incorporate unique strains with the right characteristics for specific microbial challenges. Furthermore, analysis of microbial pro- files in important poultry-producing regions worldwide can guide product development and innovation by identifying important microorganisms in challenged or underperforming flocks, uncovering the source of subclinical performance drags, understanding microbial differences linked to regional differences in diet and management, and focusing next-gener- ation product development on unmet needs in the industry.


Figure 2 - Average quantities of marker genes for food safety-related microorganisms in caecal samples from healthy, undersized, and sick birds.


Campylobacter


0.80 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00


0.60 a a 0.50 a ab 0.40 a b 0.30 a 0.20 b a a a 0.00 Campy 165 C. jejuni C. coli ▶ GUT HEALTH | DECEMBER 2020 invA 117 0.10 a Salmonella


PHOTO: UNITED ANIMAL HEALTH Log10 Gene Copies


Log10 Gene Copies


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