Enterococcus infections reduce hatchability and increase early mortality

To read more content about AviNews March 2024

The average broiler hatchability rate has decreased in the USA in the past decade.

hatchabilityFigure 1. Average hatchability of the broiler US industry between 2012 and 2022 according to hatchery egg set capacity from
650,000 to 1.5 million eggs per week. Source: AgriStats (Fort Wayne, IN)

Figure 1 shows data from AgriStats (Fort Wayne, IN), the biggest USA benchmarking company, showing the decline in hatchability between 2012 and 2022 by hatchery egg set capacity per week.

Currently, average hatchability could be close to 80%, which is five percentage points lower than it used to be in 2012.

AgriStats data indicates that between 2020 and 2023, the average broiler hatchability reduced by at least three percentage points.

Potential causes for hatchability losses

There are several potential causes for hatchability losses.

  • But, the relative importance of each bacteria has not been clarified.
  • However, Enterococcus faecalis is also associated with first-week mortality of chickens.

Enterococcus faecalis

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These microorganisms are ubiquitous in the poultry production environments and commensals in the avian gastrointestinal tract. They can become opportunistic pathogens but are also part of healthy hatchlings’ normal gut microbiota.

Dr. Jodi Delago recently reported results from a field survey conducted in six USA hatcheries at the International Poultry Scientific Forum (IPSF) in Atlanta, Georgia.

The coinfection of both bacteria was much more frequent (43 %) than the prevalence of each bacteria alone.

Other research reports indicated that Enterococcus faecalis can penetrate the eggshell, evade immune barriers in the egg, and colonize systemically.

The coinfection with both bacterium enhanced pathogenicity, resulting in increased mortality of embryos and neonatal chickens.

Enterococcus faecalis is most pathogenic

However, some experiences show Enterococcus faecalis has a more relevant role in embryo and young chick and pullet pathogenicity.

Dr. Hugo Ramirez from Mississippi State University also presented at IPSF a compilation of diagnostic cases between January and October 2023, indicating the impact of Enterococcus faecalis on broiler and pullet breeder mortality cases. Information from 93 cases of 1- to 7-day-old broiler and pullet breeder cases and 45 hatchery cases were used.

These advanced modern lab analyses provide great credibility to bacteria identification.

The results indicated that Enterococcus spp. was isolated from all evaluated yolk sac samples.

Enterococcus cecorum

Enterococcus cecorum is another gut commensal microorganism that causes considerable broiler industry losses due to sepsis and osteomyelitis.

Effective treatment and control methods like vaccination have been challenging to develop since commensal and pathogenic strains only differ in genomic features, including alterations in capsular polysaccharides.

Mitsu Suyemoto from the College of Veterinar y Medicine at North Carolina State University presented at the IPSF a study where pathogenic Enterococcus cecorum strains were genetically modified for genes that encode capsular biosynthesis (cpsC and cpsO).

This study demonstrates that two specific deletions of the bacterium genome eliminate the pathogenicity of E. cecorum. This information could be helpful to understand better the pathogenesis of E. cecorum and the development of control strategies.

Enterococcus cecorum could infect embryos during in ovo vaccination or the hatching period.

James Higuita from the University of Arkansas presented a study demonstrating that embryos can be infected by virulent strains of E. cecorum by in ovo injection into the amnion with 104 cfu/embryo at 19 days of incubation.

When the infected embryos commingled with non-infected embryos, these also became infected.

The infection affected performance as early as seven days post-hatch. The E. cecorum was recovered from all chickens’ guts, spleens, and FTV after day 26. Lesions were also observed as:

Dr. Marcela Arango from the same research group at Mississippi State University presented another summary of 299 cases received at Mississippi State University’s Poultry Research and Diagnostic Laboratory (PRDL) from January to October 2023.

This study analyzed the distribution of Enterococcus spp. and the pathogenicity of the isolated strains by determining mannitol metabolism or detecting the cpsO gene.

These results indicated the high prevalence of pathogenic E. cecorum in broilers and commensal E. cecorum in breeders. These results confirmed that mannitol metabolism could be a tool to detect E. cecorum pathogenicity.

This study demonstrated how this infection can occur and disseminate and the potential negative impact on broiler growth performance.

Control of Enterococcus is still a difficult task

The in ovo administration of commensal non-pathogenic E. cecorum could also cause competitive exclusion of pathogenic E. cecorum.

Still, dose, frequency, and route of administration require further investigation, as demonstrated by Grayson Walker from NC State University during the IPSF.

Specific bacteriophages have also shown potential to control Enterococcus spp.







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