Slack biosecurity practices remain an issue in BVD eradication programme
BVD measures will deliver €90m net savings for dairy and beef farmers this year
With around 70pc of this year's calves born and tested for BVD, the prevalence of persistently infected (PI) births has reduced to 0.03pc - a 20-fold decrease since the start of the compulsory testing programme in 2013.
Animal Health Ireland (AHI) estimates that the net benefit to farmers from this massive improvement will be worth €90m this year alone.
However, despite these successes, investigations of herds which contained PI animals continue to reveal troubling biosecurity practices that need to be improved.
Investigations of herds with PI births in 2018 found that 15pc of these could be attributed to contact with PI calves in the previous year, with a further 10pc of PI births attributed to the introduction of Trojan dams.
Furthermore, investigations in previous years highlighted the role of Trojan dams (purchased pregnant animals which are carrying a PI calf) in introducing BVD into previously free herds.
Already in 2019, 7pc of PI calves detected have been born to dams that entered the herd within 240 days of calving and were, therefore, potential Trojan births. That's according to statistics published in the Veterinary Journal last month on the results of mandatory investigations by vets of farms which had animals that tested positive for BVD.
Since 2017 all herds with test-positive calves are required to undergo a herd investigation by the Targeted Advisory Service on Animal Health (TASAH). This is undertaken by a trained veterinary practitioner within three months of the initial positive result.
Dr Maria Guelbenzu, BVD programme manager with AHI, carried out a detailed review of the results of the 737 investigations that were completed during 2018.
Just under 50pc of the investigated herds were beef, 42pc were dairy and 9pc were of dual purpose.
The investigations found that 6pc contained a persistently infected (PI) animal at the time of the visit and 26pc contained animals of unknown BVD status.
Of the 6pc of herds with PIs present at the time of the investigation in 2018, 35pc had retained the PIs for more than five weeks after the initial positive test.
In addition, in 15pc of all the investigations there were one or more PIs present during part or all of the window of susceptibility (WOS) of the dams whose calves triggered the investigation.
The WOS is the time between approximately Day 30 and Day 120 of pregnancy, when infection of the dam with BVD virus may result in the birth of a PI calf.
Therefore in 15pc of cases, the presence of a PI the previous year was identified as the cause of the PI birth in 2018.
With the purchase of animals recognised as another key risk factor for the introduction of BVD, the investigations also found that in 45pc of herds, there were animals added to the herd immediately prior to the WOS.
In 64pc of cases, the introduced animals had contact with cattle from other herds during the sale/transport process, increasing the potential for these animals to become transiently infected.
In 10pc of cases the investigated herd's cattle left the herd and subsequently returned during the WOS e.g. from shows or unsold from sales. These animals could also have acquired a transient infection, and again were typically reintroduced without any quarantine.
In 79pc of the herds, dams of PIs were grazing at a boundary at some point during the WOS.
The investigations found that in only 52pc of these herds was the quality of the boundary reported to be sufficient to prevent nose to nose contact and in 55pc to prevent the break in or out of cattle.
Of the investigated herds, just 20pc were reported to be vaccinating for BVD (17pc of beef, 25pc of dairy and 10pc of investigated dual herds).
New measures on Trojan dams
A number of changes to the investigations have been introduced for 2019.
Overdue investigations (> 3 months) will be referred to the Department of Agriculture, which will contact herd owners to advise that failure to have the investigation completed by their chosen private veterinary practitioner within the following four weeks will lead to it being carried out by a Veterinary Inspector.
Also, to minimise the risk of sale of Trojan dams from herds with positive results in 2019, vets will, as part of the TASAH investigation, advise herd owners that they should not sell animals that were pregnant at the time of removal of the last PIs unless they are antibody-negative to a sample collected within two weeks of sale.
The programme database will be used to identify the birth of calves with positive or inconclusive results that could be due to Trojan dams.
These will be traced back to their source herds.
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