AHI stress vital few BVD PIs remain on farm
“Good progress has been made by the end of the first year of the compulsory phase of the BVD eradication programme in Ireland, with a significant reduction in disease incidence and very strong levels of compliance by farmers with the programme requirements.”
This is according to Animal Health Ireland (AHI). It is again stressing with the impending start of the breeding season for many herds around 1 May, AHI said it is vital that as few PIs as possible remain on farm at that date to prevent a further cycle of transmission that will result in the birth of another round of PI calves in 2015.
According to AHI, this will require an even greater emphasis on the implementation of key biosecurity measures.
In a review of 2013, AHI found the level of compliance by farmers with the requirement to tag and test all calves born after the 1 January 2013 was very high.
“At the end of January 2014, just 14,800 of the approximately 2.1 million calves registered in 2013 remained untested. When calf deaths are taken into account, only 6,600 (0.3 per cent) 2013-born calves are alive and untested,” it outlined.
According to AHI, the overall test results for tissue tag samples in 2013 indicated that 0.8 per cent of calves had a positive or inconclusive result.
“This figure fell to 0.67 per cent when the results of negative confirmatory testing were taken into account.”
Of note, AHI found overall some 11.25 per cent of herds tested in 2013 had one or more positive results with some 14,000 PIs identified.
It elaborated: “In February 2014, approximately 10,250 of these were recorded as dead, while 3,750 were still alive in some 2,500 herds (three per cent of breeding herds), based on data held on the Department of Agriculture’s Animal Identification and Movement System (AIMS).”
It terms of preliminary results so far this year, to date tissue samples from some 373,000 calves have been tested.
“Relative to 2013 the numbers testing positive or inconclusive on initial test has reduced from 0.8 per cent to 0.44 per cent. The level of empty tags is also lower this year (0.87 per cent compared to 1.16 per cent), reflecting greater familiarity with the use of tissue tags.”
AHI also found when data is analysed on a week-by-week basis (percentage PI calves born) rather than on an annual basis, it is evident that the highest incidence of PI births (1.21 per cent) occurred at the end of July 2013.
It observed: “Since then the overall trend has been progressively downward, the lowest value of 0.38 per cent having been recorded in the last week January 2014, with the incidence remaining relatively steady since then.”
AHI also found that calves born PI at the end of July 2013 will have been infected as unborn calves in early pregnancy some 30 weeks previously, ie in early January 2013.
“Therefore the downward trend in birth of PIs from July onwards is a consequence of a downward trend in the creation of PI calves from the earliest stages of the compulsory programme.”
This indicates that measures within the programme, including the early identification and removal of PI calves and the prevention of movement of PI animals between herds have had an almost immediate impact.
According to AHI, however, it should be recognised that the PI calves being born now were created within the compulsory phase of the programme.
“This highlights the importance of key eradication measures within the programme, including the prompt testing of calves (and their dams where positive), the prompt removal of PIs when identified and the performance of wider herd investigations following positive results to identify and remove further PI animals if present.
“It is vital that herdowners do their utmost to avoid the introduction of infection through the purchase of animals (including Trojans) of unknown status without adequate quarantine and testing, or as a result of boundary contacts.”
In terms of key biosecurity measures for 2014, it continues to be the strong recommendation from AHI and its BVD Implementation Group that PI animals are removed as quickly as possible after identification.
“While a minority of these may survive to salvage weight, their retention on-farm creates an enormous risk of infection spreading from these animals to susceptible pregnant animals in the farmer’s own or neighbouring herds, resulting in the birth of further PI animals in the following season.”
A recent AHI analysis of results from herds that had PIs born in 2012 and again in 2013 clearly show that the number of PIs born in 2013 increased in proportion with the length of time that 2012-born PIs were retained.
“Indeed 29 of the 30 of these herds that had six or more PIs born in 2013 still had a 2012 born PI alive in them at the time of the analysis,” AHI outlined.
A PI heifer or cow will always produce a PI calf so the dams of calves with positive or inconclusive results are also under suspicion of being PI.
“Testing of these DAMPI animals in 2013 found 6.5 per cent to be positive,” according to AHI. “The remainder were negative, with their calves having been born PI as a result of transient infection during early pregnancy. This in turn is typically due to their having contact with a PI animal. These figures highlight the importance of the prompt identification and removal of PI animals in preventing the birth of further PI calves.”
AHI results for 2013 showed that approximately 620 herds with positive results had PIs born to animals that were in calf when introduced (Trojan animals). “Analysis of the identities of these animals suggested that in some cases (120 herds) these were returning to their birth herds, after being bred in another herd,” it noted.
Meanwhile, changes to legislation is under way. The BVD Order 2012 will very shortly be replaced by the BVD Regulations 2014.
The two principal changes from the existing legislation are the introduction of a specific prohibition on untested calves born after 1 January 2013 from being moved to slaughter, and the establishment of the Veterinary Laboratory Services of the Department of Agriculture, Food and Marine as the National Reference Laboratory for BVD.
Calves on grass. Photo O’Gorman Photography