Dr David Graham, Programme Manager for Biosecure Diseases, Animal Health Ireland.
The prompt removal of PI cattle by culling of calves or slaughter of older animals is vital to the success of the national BVD eradication programme.
During 2013 some herd owners retained PI calves in an attempt to rear them to slaughter weight. While this practice is understandable at one level, it goes against the strong advice of the BVD Implementation Group and, in the majority of cases, will have been a futile exercise, as the PI animals will have died before reaching a suitable slaughter weight.
By retaining PIs on farm, herd owners are retaining a source of infection that may well create a further crop of PI calves the following year, due to contact between these animals and breeding animals in the critical stage (30-120 days) of pregnancy. There is now clear evidence that this has happened in herds where PIs were retained since the start of the national eradication programme.
The compact breeding season in many Irish herds increases the risk associated with retaining PIs, since the majority of the breeding herd will be in early pregnancy at the same time. For this reason retaining even a single PI animal may lead to the birth of multiple PI calves the following year, creating an even worse situation. Unfortunately, there are clear examples of where this has happened, even where herd owners believed that the PI animals had been adequately isolated. To maintain the good progress made in the eradication programme to date, all PI animals should be removed as soon as possible and certainly in advance of the start of the breeding season.