Chance for healthier herd
By Richard Allison
LOSING a dairy herd to foot-and-mouth is an agonising experience, but careful planning and biosecurity measures can improve herd health after restocking.
The Agricultural Research Institute of Northern Ireland, Hillsborough, had to restock its dairy herd after a case of brucellosis two years ago.
It was a chance to improve herd health, says Sinclair Mayne, the institutes head of dairy research. "We had to salvage something from the traumatic experience."
The first step in the restocking process was to establish a group of researchers and veterinary experts to oversee the process. The first issue considered by the group was whether high health status could be sustained over time.
"This must take account of whether the herd will remain closed after restocking and have contact with neighbouring livestock. There is no point in restocking with high health stock when they are in close contact with cattle on a neighbouring farm," says Dr Mayne.
"High health animals do not have the chance to develop natural immunity, so are at greater risk when facing disease challenge.
"The group also considered which diseases to target when selecting new stock. Tuberculosis (TB), Johnes disease, enzootic bovine leukosis (EBL) and brucellosis topped the list. To date, all four diseases have been kept out of the new herd," he adds.
Other infections considered were mycoplasma bovis, bovine viral diarrhoea virus (BVD), infectious bovine rhinotracheitis (IBR) and neospora caninum. But evidence of previous exposure was found in most UK and Dutch cattle tested, leading Dr Mayne to believe it is only practical to select animals free of N caninum.
"Extensive controls would be needed to keep all these diseases out of a herd, which would involve great expense. To ensure the institute selected animals that did not carry BVD, all calves born after restocking were tested. And to prevent reintroduction of BVD and IBR, cows were vaccinated," adds Dr Mayne. "Stock was also vaccinated against salmonella and leptospirosis." Lameness is a big cost to producers, so animals displaying any symptoms or with a history of it were also avoided, particularly digital dermatitis. All animals were thoroughly examined. An additional precaution at Hillsborough was to footbath cattle three consecutive days after arrival on farm.
Dr Mayne urges producers to involve their vet when planning restocking. "This is a large investment and the last thing you want is to get it wrong, resulting in a herd with more health problems and lameness than before."
Animals were also bought directly from as few farms as possible to minimise chances of bringing back disease. The main benefit of buying directly is that disease history of the herd is known and its vet can provide details of health status, says Dr Mayne.
Teasgascs Moorepark Research Station, Co Cork, also took extra precautions when restocking after it, too, lost its herd. "These included treating cattle with antibiotics and wormers and vaccinating them against IBR and leptospirosis. They were also segregated into groups according to which herd they came from," says Teagascs Kevin OFarrell.
"Groups were inspected four times a day for signs of impending abortion. Abortions and stillbirths were also investigated for brucellosis."
In addition, animals were calved in isolation and kept in weekly calving groups until the whole herd tested clear of brucellosis.
"The whole restocking process involved 7222 blood and serology tests during the first year resulting in a herd free from TB, brucellosis, M bovis and mycobacterium paratuberculosis," says Mr OFerrell. *
• Involve vet from the outset.
• Consider which diseases to target.
• Identify herds with clean TB and brucellosis history.
• Buy directly, from few herds.
• Group animals according to source.
• Footbath cows for digital dermatitis.
• Calve animals in isolation.