Predict and prevent rather than test and treat: Sibley

THERE are a number of steps which can be taken to prevent the spread of TB in cattle which are currently not practised in Northern Ireland, according to chief guest speaker Richard Sibley, a vet from Devon, who addressed the Pedigree Cattle Trust’s conference in Portadown last week.

Fed up with testing cattle and seeing herds in his practice fighting a losing battle to escape the unending cycle of breakdowns and frequent tests, Mr Sibley worked with some proactive farmers to devise new means of eradicating TB from their herds.

A thorn in the side of DEFRA chiefs, Mr Sibley has introduced novel tests which have detected TB in stock which have passed the skin test on up to 30 occasions. He has also used a second test which detects TB in manure, with infectious cows being culled despite clear skin tests. He is also concerned about the risk of slurry as a source of infection.

Mr Sibley explained that in any herd there will be cows which are innately immune, some will be infected but the infection lies in a latent state and most of these cows never become infectious, while there will be some cows which are infectious and he says these must be identified and culled to have any hope of eliminating the disease on a farm.

He drew parallels with the human population, saying that one-third of the world’s human population is infected with TB but not all either show symptoms or are infectious to others. He said that one of the contributing factors to TB developing in humans is HIV which lowers the immune system.

Mr Sibley said that in one of the herds he had worked with, a single animal which was a BVD PI had its immune system compromised by the BVD which made it more susceptible to TB and meant it shed huge amounts of TB infection. Once it was culled from the herd the incidence began to fall dramatically.

Mr Sibley suggested four pillars to control TB:

q Biosecurity – try to keep it out in the first instance;

q Surveillance – find the carriers in the herd, especially those which are infectious;

q Resilience and immunity – how susceptible is your herd, vaccination may be an option; and

q Biocontainment – reduce the risk of spread, including early culling of infectious animals.

Predict and prevent should be the ethos rather than test and treat, said Mr Sibley.

One of the tests used by Mr Sibley is PCR which will look for shed fragments of the organism and this can be followed up with the phage test which is a very sensitive test of a blood sample to detect infected animals. He said it is important to differentiate between infected and infectious animals.

Commenting on the skin test, Mr Sibley said that it is about 50-80 per cent sensitive, but it depends how well it is done. He also said that the authorities could improve the sensitivity if they were to scrap the top lump, improving accuracy to 95 per cent.

He also questioned why it must be put in the side of the neck – in New Zealand, where they have done away with the second injection, they put the test in the tail which is much quicker and safer.

On the threat from badgers, Mr Sibley said that they test faeces from badger latrines and have found 70 per cent to be positive. He also said that where cows have been found to excrete infection in their manure, it will enter the slurry tank and then be spread on land. One of the farms he has worked with has now stopped spreading slurry on grazing pastures.

The slurry may also be passing TB to the badgers who tend to be attracted to recently spread fields to harvest worms which have been brought to the surface by the slurry.

To reduce the amount of infection in the slurry, one of the farms he works with now culls any cow which is positive on the PCR test.

Mr Sibley has also done some work on infection clusters of cows in a herd born within a short time of each other. He suspects they may have picked up infection at birth, either from contaminated milk or from infection in the calving yard from an infectious cow.

Mr Sibley concluded by saying that the system at present isn’t working and farmers are disillusioned. However he said that there are different ways of dealing with the problem, depending on the farm.

Farmers should be given options on how to get rid of TB with control tailored for the individual farm.

He said it is important to manage all the risks – you must do it all, he emphasised.

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