Johne’s disease, caused by the bacterium Mycobacterium avium sub-species paratuberculosis, or MAP for short, is characterised by a long incubation period before irreversible diarrhoea and terminal weight loss. Infection can occur at any age but is most common via the faeco-oral route within the first hours, days or weeks of life, although clinical signs are frequently not seen until between two and six years of age. Prior to this, however, there is a progressive loss of performance; both fertility and milk yield are reduced, so infected cows are less likely than uninfected herd contemporaries to conceive at the desired time and, even if they do, their reduced milk production will have consequences for the growth of their calf. Many MAP-infected suckler cows are culled as a consequence of this poor fertility or poor calf performance before the cause is recognised as Johne’s disease. Therefore, the presence of the disease within the herd and its prevalence are often not recognised.
Hygiene around the time of calving is vital in the control of Johne’s disease. In the dairy herd, where calves are reared away from the cows, this is relatively easily achieved by snatch calving in cleaned and disinfected calving boxes and feeding pasteurised colostrum. These are not usually viable options in the suckler herd but it is still possible to reduce transmission; instead of calving indoors in February, which ensures every new born calf is exposed to a concentration of faeces from the maximum number of cows possible, why not delay calving for a couple of months and calve outside on extensive pasture, allowing each cow that calves to leave the herd for a short while to deliver her calf away from the faecal contamination from other cows?
Herds that purchase their breeding replacements also face the challenge of the health status of their replacement stock being dependent on how they were managed when they were born and during their early life on their farm of origin. A proactive approach, however, can repay the cost many times over. Blood sampling and testing all breeding stock each year will usually allow the early detection of infected animals which can then be culled at a time convenient to the farm business, before they start to shed a significant amount of the infectious organism into the farm environment to infect other animals and before they start to lose weight, thereby achieving maximum value for them.
If you would like to discuss Johne’s disease control in your herd, or any other aspect of your herds management or performance please do not hesitate to speak with your routine vet.
Keith Cutler – Synergy Farm Health, Veterinary Surgeon BSc BVSc DipECBHM MRCVS
RCVS Recognised Specialist in Cattle Health and Production
