By Stephen Cadogan
Milk pasteurisation is one tool in the armoury to control Johnes Disease, rather than a silver bullet, according to Animal Health Ireland (AHI), which oversees the programme for control of Johne’s Disease in Ireland.
Calf hygiene remains the crucial control component.
Pasteurisers are useful in reducing risk, but are best used with low-risk colostrum or milk, and should not be used to attempt to ‘sterilise’ high-risk milk.
There is some evidence that the MAP bacterium which causes Johne’s Disease may be more sensitive to low temperature long time pasteurisation, where milk is heated to 60-65 degrees Centigrade for up to one hour.
Temperatures above 62 degrees are unsuitable for colostrum, significantly reducing its immunoglobulin, leaving calves fed the colostrum with increased susceptibility to disease. The current recommendation with many of the purpose-built commercial pasteurisers is to heat colostrum to 60 degrees for 60 minutes.
AHI says colostrum pasteurisation may be of use in farms as an additional layer of security to reduce MAP content.
The main advantage is the convenience of having a local source of low-risk milk, if it is taken from test-negative, low-risk, and antibiotic-free cows. It may also be useful on farms where there is difficulty in tracing transition milk from dam to calf.
Disadvantages include the cost of the equipment and the technical input for installation, calibration and ongoing maintenance.
After pasteurisation, the milk or colostrum, if not fed immediately, should be stored in a refrigerator at four degrees in capped bottles or lidded containers, and used within two days; or frozen, for longer-term storage.
AHI recommends pasteurised colostrum or milk from Johne’s Disease test-positive or high-risk animals, or from any animals in heavily infected herds, should not be used to feed calves that will be retained for breeding.
AHI also warns that MAP bacteria may survive pasteurisation.
Most MAP in milk is from faecal contamination.
It is therefore critical that milk for feeding to calves is collected meticulously, to avoid faecal contamination.