Picking the right bird for the job: disease resilience in heritage breeds

By Jeb Owen, Department of Entomology, WSU

With support from a CSANR BIOAg grant, Jeb Owen tested whether heritage chicken breeds carry built-in resistance to the parasites and pathogens that plague open-environment farms.

Chart titled "Cage-free share of U.S. egg-laying hens and lay rates, Jan. 2018–July 2023" shows that the cage-free share of egg layers has steady increased from less than 20% to nearly 40% between 2018 and 2023 while the lay rate for cage-free has converged with that of the historically more efficient non-caged birds.
Cage-free egg-laying hens as a share of all U.S. egg layers, approaching 50% of the market. Source: USDA-ERS, 2024.

Open-environment poultry production (cage-free, free-range, and pasture systems) has grown dramatically in recent years.1,2 Today, roughly 42% of U.S. eggs come from these systems,3 and market demand suggests that number should be 76% by 2026.4 But chickens that roam and forage are also more likely to encounter parasites and pathogens because they come into direct contact with feces, contaminated soil, and wildlife.1 5, 6

Surveys of open-environment farms have found that 80 to 100% of birds carry at least one external parasite species, and 100% are infected with at least one internal parasite.7

The parasites found in open-environment systems are harmful to chicken health and costly to production. For example, Eimeria sp. is a protozoan parasite that infects the lining of the gut and can cause significant tissue damage. Campylobacter jejuni is a gut bacterium detected on 85% of these farms.1 Campylobacter rarely harms the birds themselves but poses a food safety risk for people who consume contaminated eggs or meat.

Unlike conventional producers, organic farmers cannot rely on parasiticides and antibiotics. Organic certification standards restrict the use of these treatments, leaving farmers with limited options for disease control.

Breeds as a disease-management tool

Chart showing the frequency of each poultry breed accross 27 open environment farm, with Sex Link (crossed breeds), Rhode Island Red, and Plymouth Rock being the most commonplace.
Poultry breeds observed across 27 open-environment farms. Crosses such as Red Star are most common; White Leghorn appears far less frequently than non-conventional breeds.

Heritage and non-conventional chicken breeds commonly used on open-environment farms are more genetically diverse than the White Leghorn, which is used in roughly 90% of caged production.1 That diversity includes variation in immune systems that might translate into real differences in how individual breeds respond to infection.

Working with PhD student Kendra Weston and collaborator Dr. Michael Konkel (WSU Department of Molecular Biosciences), we obtained day-old chicks from seven non-conventional breeds: Rhode Island Red, White Rock, Barred Rock, Black Star, Ameraucana, Silver-Laced Wyandotte, and Black Australorp. The chicks were raised in controlled environmental chambers and then each inoculated separately with Emeria and Campylobacter—two organisms common on open-environment farms.

After one week of infection, we examined gut tissue for lesions caused by Eimeria and tested for Campylobacter. Each experiment was run twice to confirm the results.

Box plot showing breeds on x axis and infection intensity score on y axs. Intensity scores ranged from means of 1 t0 3 with full range going from 0 to 6. White Rick and Wyandotte showed the highest infection intensities.
Boxplots of visual lesion scores from intestines of chickens infected with Eimeria sp. parasites. Silver-Laced Wyandotte (arrow) had the lowest scores across all areas of gut tissue (Kruskal-Wallis Test P<0.05)

What we found

Every bird exposed to Eimeria became infected; no breed was immune. But what varied significantly was how much damage the parasite caused: some breeds showed relatively low lesion scores.

The picture was different for Campylobacter. Here, infection rates varied sharply by breed. Silver-Laced Wyandotte chicks were colonized at a rate of 57%, while Ameraucana and Black Australorp chicks showed only 6% infection rates. Barred Rock, Black Star, Rhode Island Red, and White Rock birds showed no colonization at all.

The Silver-Laced Wyandotte showed relatively low lesion scores for Eimeria but was the breed most susceptible to Campylobacter colonization. These results suggest possible trade-offs in the defenses effective against these two organisms and underscore the need for continued research before breed selection can be recommended as a management strategy.

Implications for farmers

The practical implication is that farmers may be able to select breeds that are naturally more resistant to the specific disease pressures on their operation. Farmers might reduce the number of infected birds in a flock, or reduce the damage infections cause, without relying on the parasiticides and antibiotics that organic certification restricts.

It’s important to note what this research doesn’t yet answer. The experiments were conducted on two-week-old chicks, and it’s not yet clear whether the same breed differences hold in adult birds, which matter more to the farm’s economic bottom line. The study also tested infections separately; on real farms, co-infections with multiple parasites and pathogens simultaneously are common.1 Those interactions remain unstudied.

Next steps

Future work will need to test a broader range of parasites and pathogens under real farm conditions. Economic outcomes like egg production, feed efficiency, and growth rates will also need to be measured alongside disease resistance to give farmers a complete picture. Ongoing surveillance on farms will be important so producers can make informed decisions about breed selection as one tool among many for managing disease.

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References

  1. Cornell, K.A., Smith, O.M., Crespo, R., Jones, M.S., Snyder, W.E., Owen, J.P. (2021). Prevalence patterns for enteric parasites of chickens managed in open environments of the Western United States. Avian Diseases.
  2. Blatchford, R. (2024). Alternative housing for laying hens: Access to outside. Poultry Extension Collaboration. Aug 2024, Vol. 53. Accessed 3 November 2025.
  3. United Egg Producers. (2017). 2025 Animal husbandry guidelines for U.S. egg laying flocks. Accessed 3 August 2025.
  4. Oberholtzer, L., Greene, C. & Lopez, E. (2006). Organic poultry and eggs capture high price premiums and growing share of specialty markets. US Department of Agriculture, Economic Research Service.
  5. Lay Jr, D. C., R. M. Fulton, P. Y. Hester, D. M. Karcher, J. B. Kjaer, Joy Ann Mench, B. A. Mullens et al. (2011). Hen welfare in different housing systems. Poultry Science. 90: 278-294.
  6. Chambless KN, Cornell KA, Crespo R, Snyder WE, and JP Owen. (2022). Diversity and Prevalence of Ectoparasites on Poultry from Open Environment Farms in the Western-United States of Washington, Idaho, Oregon, and California. Trout Fryxell R, editor. Journal of Medical Entomology. 59(5):1837–1841.
  7. Murillo AC, Mullens BA. 2016. Diversity and Prevalence of Ectoparasites on Backyard Chicken Flocks in California. Journal of Medical Entomology. 53(3):707–711.