Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2009
Publication Date: 7/12/2009
Citation: Byrem, T.M., Norman, H.D., Wright, J.R. 2009. Characteristics of milk ELISA results for Johne’s disease in US dairy cows. Journal of Dairy Science. 92(E-Suppl. 1):386-387(abstr. W8). Interpretive Summary:
Technical Abstract: The expanding practice of using antibody-capture ELISA on DHIA milk samples to test cows for infection with Mycobacterium avium subsp. paratuberculosis (Johne’s disease) produced data for further study. Milk ELISA results (196,412) from 696 herds in 16 states between 2002 and 2008 had a mean score of 0.04, a standard deviation (SD) of 0.18, and revealed 3.2 and 6.1% positives based on cutoffs of 0.40 and 0.10, respectively. A subset of data (42,778) from more comprehensive testing in 25 herds from Michigan and Wisconsin had a mean score of 0.04, a SD of 0.18, and 3.0 and 5.6% positives based on cutoffs of 0.40 and 0.10, respectively. For cows with multiple tests within parity (12%), those with negative scores (<0.10) on the first test were negative on the last test 94.6% of the time. Cows with positive scores on the first test were positive on the last test 51.7% of the time. For cows with multiple tests across parities (36%), equivalent frequencies were 90.9 and 47.0%. Within herd and year, differences in milk yield (lbs) between cows with negative and positive ELISA results based on cutoffs of 0.40, 0.10, 0.06, 0.04, 0.02, and 0.00 were 528, 479, 404, 316, 295, and 305 kg, respectively. Differences in milk yield were similar until the cutoff for ELISA score exceeded 0.05, suggesting a point where a notable percentage of infected cows were included in the positive group, thereby revealing their lower productivity through mean milk yield. Untested cows had lower mean milk yield than tested cows, even those whose test was positive. Examining the termination code for positive, negative, and untested cows revealed an unusually high percentage (44%) of the untested cows were removed from the herd by the end of the current lactation. This was in contrast to 15% of the positive cows and 12% of the negative cows being removed from the herd. Test day records from DHIA are an important source of information for the analysis of milk ELISA testing programs for Johne’s disease.