Does it make sense to test all of your heifers for Johne’s disease so that you can remove positive animals from your herd earlier? Researchers at the University of Idaho and Michigan State University conducted a case-control study to find out. The results were published in the June Journal of Dairy Science.

What they learned was that there was no significant difference in herd longevity, production performance, and adult Mycobacterium avium ssp. paratuberculosis (MAP) test status between cows testing positive for MAP before two years of age (by either fecal culture or serum ELISA) and their herd-mates. Based on these results, it appears that the MAP test status of young dairy replacements, using currently available tests, is not a reliable indicator of true infection status or future impaired production over the course of the current average lifetime of Holstein dairy cattle, say the researchers.

Therefore, they say that testing young dairy replacements, using currently available tests, is not justifiable from a purely economic point of view. However, from a disease-control standpoint, early identification and removal of MAP-infected animals is always prudent and further research is warranted.