A large proportion of cows tolerant to the disease of the Mycobacterium avium subspecies paratuberculosis comparable to the number of susceptible cows is of great interest for genetic selection
Citation
Bissonnette, N., D. Kelton, G. Fecteau, K. Tahlan, E. Ibeagha-Awemu, and P. Griebel. 2022. Identification of disease tolerant and susceptible cows to Mycobacterium avium subspecies paratuberculosis infection for genetic analyses of disease resistance. 15th International Colloquium on Paratuberculosis. Dublin, Irland, June 12-16 2022.
Plain language summary
Some cows exposed to Mycobacterium avium subspecies paratuberculosis (Map) progress to clinical Johne’s disease (JD). Disease progression is unpredictable in large part because of individual host resistance. Host genetic variation contribute to resistance and progression toward clinical stage, i.e. tolerance. To identify genetic markers associated to tolerance, i.e. cows with the ability to cope with the infection, phenotypes of fecal Map-excretion and Map-specific blood antibodies (Map-Ab) were collected from cows older than 2 yrs for a period of 3-5 yrs. These cows have been exposed to Map in a similar way. Blood and fecal samples were collected 2 times/yr and tested for Map-Ab (Idexx) and for Map-specific ISMAP02 (VetMAX™-Gold MAP Detection Kit) by direct fecal qPCR. We report individual profiles from the highest Map prevalent herd from 23 dairy herds studied.
The fecal Map excreting and blood Map-Ab profiles revealed great variability at the individual response to a similar Map exposure. From the 3452 cows tested, 547 were identified as JD susceptible. Out of these, 169 were considered high shedders since they excreted >106 CFU/g feces earlier in life, while 378 that excreted 103-5 CFU/g feces and were blood positive for Map-Ab in one of the samplings were also considered susceptible. Interestingly, after the 2-yr susceptible period, 616 cows showed a latent period greater than 6 yrs during which shedding level was low to negligible, but fluctuations of blood Map-Ab were observed.
A combination of fecal Map-shedding and blood circulating Map-Ab collected in the longitudinal study allowed us to identifying cows with longer latency and incubation period and with lower shedding level while potentially infectious than JD susceptible cows. This descriptive analysis highlights the potential for selecting cattle more resistant to JD by identifying genetic markers associated with the infection progression and shedding levels of MAP.
Abstract
Some cows exposed to Mycobacterium avium subspecies paratuberculosis (Map) progress to clinical Johne’s disease (JD). Disease progression is unpredictable in large part because of individual host resistance. Host genetic variation contribute to resistance and progression toward clinical stage, i.e. tolerance. To identify genetic markers associated to tolerance, i.e. cows with the ability to cope with the infection, phenotypes of fecal Map-excretion and Map-specific blood antibodies (Map-Ab) were collected from cows older than 2 yrs for a period of 3-5 yrs. These cows have been exposed to Map in a similar way. Blood and fecal samples were collected 2 times/yr and tested for Map-Ab (Idexx) and for Map-specific ISMAP02 (VetMAX™-Gold MAP Detection Kit) by direct fecal qPCR. We report individual profiles from the highest Map prevalent herd from 23 dairy herds studied.
The fecal Map excreting and blood Map-Ab profiles revealed great variability at the individual response to a similar Map exposure. From the 3452 cows tested, 547 were identified as JD susceptible. Out of these, 169 were considered high shedders since they excreted >106 CFU/g feces earlier in life, while 378 that excreted 103-5 CFU/g feces and were blood positive for Map-Ab in one of the samplings were also considered susceptible. Interestingly, after the 2-yr susceptible period, 616 cows showed a latent period greater than 6 yrs during which shedding level was low to negligible, but fluctuations of blood Map-Ab were observed.
A combination of fecal Map-shedding and blood circulating Map-Ab collected in the longitudinal study allowed us to identifying cows with longer latency and incubation period and with lower shedding level while potentially infectious than JD susceptible cows. This descriptive analysis highlights the potential for selecting cattle more resistant to JD by identifying genetic markers associated with the infection progression and shedding levels of MAP.