Study Finds ELISAs in Milk Samples Less Reliable for Johne's Disease Detection -- $198M in Dairy Losses Underscore Need for More Accurate Milk Testing

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Peer-reviewed (in-press) study finds serum-based antibody tests align, but milk results vary—calling for improved milk-specific diagnostics to strengthen herd surveillance and profitability

CARLSBAD, Calif., Oct. 29, 2025 /PRNewswire/ -- Pictor Holdings Inc. today announced new peer-reviewed data showing close agreement between commercial antibody tests when used on serum, but higher variability when used on milk—findings that highlight the need for milk-specific diagnostic standards to scale Johne's disease surveillance.

Johne's disease costs the U.S. dairy industry an estimated $198 million annually (Journal of Dairy Science, Rasmussen et al., 2021). The disease, caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP), progressively damages the gut of infected cattle, reducing nutrient absorption and milk yield. It spreads primarily through contaminated feces, milk or feed.

Key Findings:

• Serum results align strongly: Two commercial antibody tests demonstrated good agreement when used on serum (κ = 0.84–0.94), showing that serum yields consistent and comparable data across kits for herd surveillance.
• Milk results show greater variability: Agreement between the different kits on milk samples was lower (κ = 0.59–0.82), reinforcing the need for purpose-built milk assays with standardized cutoff values to ensure diagnostic reliability.
• ELISA and PCR are complementary: The study reported moderate to substantial agreement between ELISA and fecal PCR results (κ = 0.43–0.74). Each method detects a distinct biomarker—ELISA detects host antibodies to MAP exposure, while PCR identifies MAP genetic material–providing complimentary insights for herd management.

Why It Matters:
Milk is a cost-effective and practical specimen type for dairy herd level surveillance, since milk sample collection is already routine. Improving the performance of milk-based antibody tests and standardizing cutoff values could make early Johne's disease detection more consistent and scalable–without relying on more invasive or higher-cost testing methods.

"Johne's disease remains one of the most under-recognized burdens in global dairy production. Even at subclinical levels, it quietly erodes milk yield, herd health, and producer profitability," said Dr. John Bannantine, retired USDA-ARS Research Microbiologist. "The wider impact reaches beyond economics—this is a disease that challenges both animal welfare and, potentially, human health. Our research is focused on finding faster, more reliable ways to detect infection early, because every day of delay compounds the loss."

"Veterinarians, dairy farmers, and dairy testing laboratories need cost-effective tests developed specifically for milk," said Dr Jamie Platt, CEO of Pictor Holdings, Inc. "Repurposing serum-based assays is not optimal and this study underscores why milk-specific test design is needed for reliable herd monitoring."  

Implications for the Dairy Industry:
The study's findings support three key actions for advancing Johne's disease control:

• Adopt milk-first surveillance strategies using assays specifically developed for milk to maintain cost and scale advantages.
• Drive industry alignment on standardized milk test cutoff values to improve result consistency and strengthen confidence in herd management decisions.
• Integrate milk antibody testing for herd screening, complemented by fecal PCR in higher-risk herds to enhance overall diagnostic accuracy.

About the Study
The paper, "A comparative study between milk- and serum-based antibody detection assays for Johne's disease in New Zealand dairy cattle," analyzed samples from four dairy herds in New Zealand. Researchers compared two commercial diagnostic kits on paired milk and serum samples, with a subset also tested using fecal PCR. The study was co-funded by Pictor Ltd. (a Pictor Holdings company) and Massey Ventures Ltd.

Although conducted in New Zealand's pasture system, these findings are relevant to dairy operations across North and South America, Europe, and Australasia. Pictor's multiplex diagnostic platform supports veterinary labs and providers with validated, off-the-shelf serum assays as examined in this study.

The abstract is now live, with the full paper set to be published soon in Tuberculosis (Elsevier). Media can request the full paper, figure pack, or interviews with co-authors and Pictor's technical team using the contact information below.

About Pictor
Pictor is a global leader in flexible and targeted proteomics, delivering next-generation multiplex diagnostics that empower clinical labs, diagnostic manufacturers, and veterinary providers. Its patented PictArray^™ platform, PictImager^™, and AI-powered Pictorial™ software enable faster, deeper insights from a single sample—helping improve outcomes in both human and animal health.

Headquartered in Carlsbad, CA, Pictor Holdings Inc. is committed to transforming diagnostics through scalable, high-performance solutions. Learn more at www.pictordx.com.

Media Contact:
Kelly Krueger
415-235-5031
[email protected] 

SOURCE Pictor Holdings Inc.