In preparation for a presentation to the 113th Annual Meeting of the United States Animal Health Association, a questionnaire was sent to members of the Association of Veterinarians in Egg Production to document the disease status of U.S. flocks. The respondents were all involved in health maintenance as diagnosticians in state and federal laboratories, consultants, company veterinarians and professionals affiliated with primary breeders and the pharmaceutical and biologics industries.

Generally the survey did not disclose any major problems relating to the health of either pullets or laying flocks. This situation is attributed to a number of factors, including:

  • elimination of vertically transmitted diseases by primary breeders,
  • diligent vaccination with live and inactivated agents, 
  • an increased awareness of the importance of biosecurity, cleaning and disinfection, and
  • implementing good production practices especially with regard to ventilation.

The survey was divided into five sections dealing respectively with caged pullets, caged layers, non-confined pullets, non-confined layers and emerging issues of concern.

Respondents were asked to rate the importance of diseases on a scale of 1 to 4 depending on severity and incidence.

‘Starveouts’ reported for caged flocks

The survey results for caged pullets confirmed problems relating to chick quality and the effect of stressful environments on viability. “Starveouts” and yolk infections were the most important conditions reported. Peripheral neuropathy, an autoimmune condition affecting the nervous system, clinically resembling Marek’s disease, appears at 5 to 8 weeks of age in replacement flocks, mostly of two strains. Coccidiosis and ILT were seen occasionally but were not regarded as significant problems in pullets.

For caged layers, E. coli peritonitis was the most serious condition followed by cannibalism and mycoplasmosis. “Calcium depletion” which is effectively osteomalacia is observed in underweight pullets subjected to early light stimulation when approaching and after peak production. Coccidiosis and focal duodenal necrosis are observed in some flocks on a regional basis.

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Fifty-year-old conditions seen

Non-confined flocks in either barns or under free-range management demonstrate the diseases and parasitic conditions observed over fifty years ago before confinement housing was universally adopted by the industry. Non-confined pullets show coccidiosis in addition to the losses during the first week associated with “starveouts” and yolk infection. Rearing on litter leads to ascarid verminosis. It is noted that capillariasis, which is frequently encountered in backyard flocks was not cited as a condition diagnosed in commercial flocks. It is possible that these parasites affecting either the crop or the intestine are missed on field examination as they are difficult to visualize and may in fact occur in free-range hens.

Among non-confined producing flocks, cannibalism and colibacillosis were the most significant causes of mortality. Mites and ascarid worms were ranked second and coccidiosis the third most frequently encountered infection.

Organic flocks treatments needed

In reviewing conditions other than disease affecting the industry, welfare issues were considered to be the most important. Absence of approved effective treatments, especially for organic flocks was noted as a significant restraint to therapy and averting mortality. The need for a broader range of more effective vaccines was stressed. Salmonella enteritidis and avian influenza were ranked highly among the concerns confronting veterinarians in egg-production.

Many of the respondents noted an increased incidence of clinical mycoplasmosis (MG) in vaccinated flocks. The F-strain vaccine appears to be less effective when administered by the spray route but frequently provides protection if instilled by eye drop. In some cases tylosin is used to suppress clinical signs of MG.

Cannibalism remains a major problem in non-confined flocks and is multifactorial in origin. Lack of socialization during the pullet phase, failure to provide perches and “escape areas,” improper beak treatment when applied at either the hatchery or at 7 to 10 days without subsequent “tipping,” and high light intensity can all exacerbate cannibalism which can result in up to 30% losses in a floor-housed flock from 35 weeks to depletion.

Diseases which were previously prevalent but are now seldom encountered include pox, cholera, coryza and erysipelas. Although infectious bursal disease is not recognized as a significant clinical condition, immunosuppression in all probability is responsible for a decreased response to vaccination and increased susceptibility to secondary bacterial agents including avian pathogenic E. coli.