Objective

The current experiment was designed to assess the efficacy of monensin to reduce pass-through fecal shedding and to reduce tissue bacterial load (Bio-burden) of MAP in calves.

Materials and Methods

Twelve neonatal Holstein heifer calves (1-3 days of age) were randomly assigned to receive a carrier containing 35 mg. Monensin (n=6), or placebo (n=6), added to the milk replacer at each twice-a-day feeding. The trial was conducted as a randomized double blind trial. All calves were administered two oral doses of viable Mycobacterium avium subsp. paratuberculosis (MAP) on two consecutive days between day 7 and 9 of the trial. Calves were euthanized between days 65 and 67 days.

Results

Calves fed monensin had fewer culture positive (55%) fecal samples, fewer total HEYM positive tubes (63%) and less MAP cfu (72%) detected in the manure compared to controls. Monensin fed calves had fewer culture positive tissues (66%), fewer total culture positive HEYM tissue tubes (68%) and lower MAP cfu (87%) in the tissues compared to controls.

Significance

Monensin effectively reduced tissue colonization with MAP following oral challenge, and also reduced fecal pass-through shedding of MAP. Monensin may act directly on Mycobacterium avium subsp. paratuberculosis by inhibiting growth of the mycobacterial cell as preliminary evidence in our laboratory has shown or it may enhance phagocytic killing of mycobacteria or both. The amount of monensin (70 mg) administered per day to calves in this study is higher than the amount that would normally be consumed by a neonatal calf in a calf starter. This study was a proof-of-concept study to determine the efficacy of monensin in controlling infection with MAP in the neonatal calf.

Notes

*Monensin™, Elanco Animal Health, a Division of Eli Lilly & Company, Indianapolis, ID 46285