An update on the health status of U.S. egg-producing flocks is presented annually to the United States Animal Health Association, Committee on Transmissible Diseases of Poultry and Other Avian Species. Currently there are no major clinical disease problems in pullets or laying hens housed in either cages or alternative systems. This is attributed to the availability of effective vaccines, enhanced supervision and management of flocks, veterinary diagnostic and technical resources and optimal nutrition.

A poll conducted among members of the Association of Veterinarians in Egg Production was conducted prior to the meeting to determine the occurrence and severity of various infections and conditions affecting commercial flocks. Respondents were asked to rate significance on a scale to 1 to 4 with 1 represented by “no problems” and 4 denoting “serious widespread problems.”

The results from 19 responses for confined flocks and 13 from flocks in alternative systems are summarized:

Confined flocks  

  • It is obvious that coccidiosis remains a problem with immature flocks but should be controlled by either vaccination either at the hatchery or within the first day of placement or alternatively using an anticoccidial feed additive.
  • The survey highlighted problems attributed to chick quality including “starveouts” and yolk sac infections. There is an obvious need to improve chick quality at the time of delivery and this can be achieved through collecting hatching eggs from flocks older than 25 weeks of age, more diligent grading at the hatchery and optimizing environmental conditions during incubation and delivery.
  • Marek’s disease appears to be a low-level problem but this is relative to the fact that there are few other diseases which are widespread and significant in their economic impact.
  • E. coli infection resulting in colibacillosis/peritonitis is a significant cause of losses in mature flocks. The importance of this condition has declined in recent years mainly attributable to the introduction and application of an effective vaccination program.
  • Focal duodenal necrosis and mycoplasmosis continue as erosive diseases, especially in caged flocks.
  • Mite infestation remains a problem in both caged and cage-free flocks.

Non-confined flocks  

Specific problems associated with non-confined flocks included:


  • Cannibalism is the leading cause of mortality in cage-free flocks. Appropriate management procedures including beak trimming, control of lighting, and “socialization” of flocks during rearing appear to alleviate losses due to this condition.
  • Coccidiosis especially when pullets are transferred from cage rearing to litter
  • Hysteria
  • Worm and ectoparasite infestation

General observations 
Diseases that may be regarded as controlled and with a low incidence include infectious laryngotracheitis, infectious bronchitis and nephrosis (gout). These conditions are usually associated with either a region or a complex. The HVT-vectored ILT vaccine is demonstrating acceptable protection in regions with high challenge and hopefully this vaccine will displace live attenuated chick embryo origin vaccines which persist and may affect broilers. Coryza is a regional disease with the clinical form suppressed by administration of bacterins. Marek’s disease is currently well controlled essentially due the application of Rispens strain vaccine frequently in combination with HVT and SB-1. The industry has relied on current combinations of types 1, 2 and 3 MD vaccines for many years but it is anticipated that more virulent strains will emerge as these products may lose their effectiveness.

The dearth of effective therapy for a number of diseases was noted as a significant problem by respondents. This is an even greater restraint to efficiency in the case of organic flocks where losses are experienced due to restrictions on the range of drugs available.

Since August 2010, SE has emerged as an important infection resulting in a single extensive recall of eggs. The introduction of the FDA Egg Safety Rule has intensified environmental monitoring and there has been a general upgrading of biosecurity, rodent control and vaccination by the industry.

Avian influenza has receded in level of concern due to the low frequency of isolation from free-living birds and absence of outbreaks in commercial poultry. The USDA-APHIS in collaboration with state veterinary regulators and the industry have developed the Secure Egg Supply Plan. This will allow movement of eggs within and beyond a quarantined area providing individual farms comply with strict pre-approved biosecurity procedure and strict surveillance demonstrating freedom from infection. The successful suppression of LPAI in the live bird market system in the Northeast has reduced the risk to egg production operations in the New England and Mid-Atlantic states.

Diseases in commercial egg production flocks are in large measure controlled by vaccination, although biosecurity is important. The industry is however still in need of improved vaccines and availability of consumer-acceptable effective medication.