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When managing dairy and suckler herds with Johne's disease present, you need to be careful, especially around calving.
The most obvious way a calf can become infected is if it consumes dirt or faeces from the teats of an infected cow. However, feeding whole milk or colostrum from an infected cow can also transfer the bad bugs to the newborn.
Pasteurisation
Pasteurising milk and biestings and then feeding calves milk powder instead of whole milk have been seen as the best methods of reducing Johne's bacteria transfer. However, neither pasteurisation nor milk powder are surefire disease blockers.
A number of weeks ago, new research showed that Johne's bacteria can actually be present in calf milk replacer – if the milk powder is made from milk products derived from whole milk where cows had Johne's bacteria.
Irene Grant and her team from Queens University in Belfast published the first report of the isolation of viable Johne's bugs from calf milk replacer.
Suckers cows with Johne's should be isolated around calving to prevent other calves getting contaminated.
Their findings raise concerns about the potential ability of the Johne's bug to survive the manufacture process of dried milk-based products. Further research on these results is ongoing.
This week, Animal Health Ireland (AHI) released updated information on what is the best pasteurisation process. AHI says there are two types of pasteurisation that can be applied to milk.
Commercial pasteurisation is a high-temperature short-time (HTST) continuous process which heats milk to around 72°C for 15 to 25 seconds.
The second form of pasteurisation is low-temperature long-time (LTLT) batch pasteurisation, where milk is heated to 60° to 65° for up to one hour. AHI suggests there is some evidence to suggest the Johne's bug may be more sensitive to LTLT pasteurisation.
Temperature problem
Although either method may be used with milk, it is important to note that neither HTST pasteurisation nor LTLT pasteurisation if carried out above 62° are suitable for the pasteurisation of colostrum. Several studies have shown significant reductions in immunoglobulin levels and thickening and coagulation of colostrum when heated to temperatures of greater than 62°.
The current recommendation is to heat colostrum to 60° for 60 minutes
Calves fed colostrum heated to these temperatures are at increased risk of diarrhoea due to changes in the colostrum consistency and failure of passive transfer of colostral antibodies, leading to increased susceptibility to calfhood diseases.
Therefore, the current recommendation which is used in many of the purpose-built commercial colostrum pasteurisers is to heat colostrum to 60° for 60 minutes.
Key points to remember
Milk from cows being treated with antibiotics should not be used for feeding to calves, irrespective of whether it is pasteurised or not. It could lead to the development of bacteria that are resistant to these antibiotics.
After pasteurisation, the milk or colostrum, if not fed immediately, should be stored in a refrigerator at 4° in capped bottles or lidded containers and used within two days.
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