University of Wisconsin Johne’s disease researcher Mike Collins has developed a new decision-making protocol using ELISA S/P values and based on likelihood ratios. It was developed to help dairy producers minimize premature culling of productive cows, while efficiently removing the most severely affected animals that spread the disease.
The system uses the numeric results from the ELISA test to classify animals as negative, suspect, weak positive, positive and strong positive. Based on those test results, Collins has rated the likelihood that animals are indeed infected and established a plan of action for animals in each category that will help limit disease spread. It can be used in any herd that has at least one case of Johne’s disease, confirmed by fecal-culture results, in a home-raised animal.
For those herds, Collins suggests the following steps:
1. Use the ELISA blood test by IDEXX Laboratories on every animal during every lactation.
2. Conduct the test between 200 and 305 days in milk. Do not test right at dry-off, as the investment and residue risk related to dry-cow therapies can complicate the picture.
3. Follow the suggested actions steps for cows that fall into each of the categories based on their ELISA S/P levels:
Suspect (S/P 0.10 – 0.25) – Keep in the herd but DO NOT use colostrum. Calve in isolated maternity facilities. Breed back and retest between days 200 and 305 of next lactation.
Weak positive (S/P 0.25 – 0.40) – Keep in the herd but DO NOT use colostrum. Calve in isolated maternity facilities. Consider Johne’s status when making culling decisions and/or considering whether to breed back. If bred back, monitor closely for clinical Johne’s symptoms and cull if any symptoms appear. Retest between 200 and 305 days of next lactation.
Positive (S/P 0.40 – 1.00) – Cull at the end of her current lactation unless an unusual circumstance dictates keeping temporarily. Do not dry treat unless kept through calving. If kept until calving, calve in isolated maternity facilities and DO NOT use colostrum. Do not breed back.
Strong positive (S/P > 1.00) – Do not dry treat. Cull at dry off.
Maureen Hanson is a freelance writer from La Porte City, Iowa.