Location: Infectious Bacterial Diseases ResearchTitle: Clinical disease and stage of lactation influences shedding of Mycobacterium avium subsp. paratuberculosis into milk and colostrum of naturally infected dairy cows Author
|Bradner, L - Iowa State University|
|Robbe-austerman, Suelee - Animal And Plant Health Inspection Service (APHIS)|
|Beitz, Donald - Iowa State University|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2014
Publication Date: 10/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59643
Citation: Stabel, J.R., Bradner, L., Robbe-Austerman, S., Beitz, D.C. 2014. Clinical disease and stage of lactation influences shedding of Mycobacterium avium subsp. paratuberculosis into milk and colostrum of naturally infected dairy cows. Journal of Dairy Science. 97:6296-6304.
Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. Shedding of this bacterium into the milk of infected dams is one mode of transmission to young calves. However, there is very little data to determine how much shedding occurs. The present study evaluates the shedding of the bacteria into colostrum and milk durinig the 305-day lactation cycle. These results are critical for producers to understand and to assess exposure of calves to the bacteria on-farm.
Technical Abstract: Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne’s disease (JD). One mode of transmission of MAP is through ingestion of contaminated milk and colostrum by susceptible calves. The objective of this study was to determine if the amount of MAP shed into the milk and colostrum of infected cows was impacted by severity of infection, as well as the number of days in milk (DIM). Milk was collected over the 305-day lactation period from naturally infected cows in the asymptomatic subclinical (n = 39) and symptomatic clinical (n = 29) stages of disease, as well as 8 noninfected control cows. All milk samples were assayed for MAP by culture on Herrold’s egg yolk (HEY) medium and either BACTEC 12B or para-JEM liquid medium, and by direct PCR for the IS900 target gene. MAP was detected in 3.8, 4.1, and 12.6% of milk samples collected from cows with subclinical JD after culture in HEY medium, liquid medium, and direct PCR, respectively. The incidence of MAP positivity increased to 12.9, 18.4, and 49.2% of milk samples collected from cows with clinical JD by these same methods, respectively. None of the milk samples collected from control cows were positive for MAP by any detection method. Viable MAP was primarily isolated from milk and colostrum of subclinically and clinically infected cows collected in early lactation (DIM 0-60); with negligible incidence observed in mid (DIM 60-240) and late (DIM 240-305) lactation. This study demonstrates that shedding of MAP into milk is impacted by infection status of the cow as well as stage of lactation, providing useful information to producers to help break the cycle of infection within a herd.