Newsletter October 2008
Firstly, Congratulations to Edna who became engaged to Binny last month. They plan to
marry next June.
Undoubtedly, one of the most worrying emerging diseases of the moment is Johne’s
disease. We are diagnosing more and more clinical cases in both dairy and beef herds.
These often present as cows that scour profusely, typically after calving. Generally cattle
are infected as calves when their gut is able to absorb the bacteria after suckling
colostrum from teats contaminated with faeces. Transmission also occurs where infected
and contaminated colostrum is pooled in batches, then fed to groups of calves, thus
causing widespread infection. In some situations where there is a large number of
infected cattle, an infected individual can infect another individual; this is rare.
Control of Johne’s disease is centred on management of the new born calf, in particular
the use of colostrum. Herds that have a known problem with Johne’s should be very
careful if allowing calves to suckle and they should only be allowed to suckle from one
cow, ideally in an individual loose box to avoid contamination of the teats by other cows’
faeces. Colostrum should not, under any circumstances be pooled or mixed and fed to
calves other than the calves belonging to the dam. Use of pasteurizers is becoming
popular now as an alternative to discarding large quantities of milk. Some colostrum
supplements are also now on the market and may allow ‘snatching’ of all calves before
suckling the dam.
Diagnosis is particularly difficult as the bacteria hides in the gut until a stress triggers the
production of large numbers of bacteria and so the disease explodes. It is not until this
late stage in the disease process that the body starts to produce a detectable level of
antibodies in the blood or detectable bacteria in the faeces. Thus a negative blood or
faeces sample must be interpreted with caution as it could have tested falsely negative. A
positive result is however, strong evidence of infection and these animals should be
culled from the herd.
The advent of a bulk milk test this year now allows us to monitor the level of herd
infection. Obviously it doesn’t tell us who the carriers are but can act as an early warning
sign to tell us to improve hygiene and husbandry around the time of calving. Individual
cow milks are also now being used in order to eliminate infection from the herd.