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BVDzero award winner – the risk of buying pregnant cattle

11th May 2019

The winning entry in the 2018 BVDzero award was submitted by vet Anna Bruguera Sala from Alnorthumbria Vet Group, Rothbury. The entry was one of 30 from all over Europe in the biennial competition.

 

Anna’s case study examined the risk of buying pregnant cattle, and focussed on a farm that was accredited BVD free for four years from 2012-2016. In 2017 it was re-infected following the purchase of some pregnant heifers, which gave birth to PI calves. The case study detailed the background to the farm, the problems which arose and the timings of those problems, and the investigations undertaken to establish what was causing them.

 

Background

 

The farm runs a beef herd and a sheep flock, with approximately 450 suckler cows (including 70 replace­ment heifers), 150 to 200 fattening cattle, 13 bulls (Charolais, Limousin and Aberdeen Angus) and 900 breeding ewes. The farm is divided into three units: the bottom and top yards that are separated by a road and a third new shed located a mile away from the other two yards. Additionally, there are three hill farms where cows are sent to graze after they have been scanned and confirmed in-calf. The farm runs a spring and an autumn calving herd, with 12-week calving periods that usually extend from February to April and August to No­vember. Spring calving takes place at the main farm, while the autumn cows mainly calve at the hill farms.

 

Bulls, replacement heifers and fattening cattle are brought onto the farm every year, mostly sourced through the market but also some private sales. On arrival, all stock is tested for BVD antigen and bulls are sourced from BVD-free accredited breeders. Historically, homebred replacement heifers were given an inactivated BVD vaccine and the farm is a member of BVDFree England.

 

There are four neighbouring farms, all with cattle and some cattle contact is always possible, as with most hill farm-type situations.

 

BVD on the farm

 

Although vaccination had been used for 10 years, the farmer acknowledged that vaccination timings may not always have been correctly adhered to and investigations into a pneumonia outbreak in 2011 confirmed the presence of BVD. After blood testing all adult cattle and antigen tag testing all calves, two PI cows were found and culled, while all calves tested negative. Regular testing in 2014 confirmed the herd was still free of BVD and twice yearly antibody checktests were then performed.

 

2018 outbreak

 

At the end of 2017, a group of 17 pregnant heifers was bought in. In a departure from previous practice, these had not been vaccinated for BVD and the BVD status of the origin farm was unknown.

 

Upon arrival, they were isolated and antigen tested; all were negative and a two-shot BVD vaccine primary course was started, although again the herdsman later conceded second dose timings often extended beyond the 4 week period as specified by the datasheet. Furthermore, when isolated, the group of cattle did come into contact with other cattle belonging to a neighbour and a BVD outbreak was diagnosed in early 2018.

 

When entering the ‘isolation’ field, many of the heifers were between 88-124 days pregnant and would, therefore, be at risk of producing a PI calf.

 

In early 2018, vets made multiple visits to the farm for cases of calf pneumonia.

The severity of the clinical signs in this group of young calves raised the suspicion that there

might have been BVD virus amongst them. In March 2018, when the youngest bought-in calf reached four weeks of age, all 17 calves were blood sampled and tested for BVD antigen. Three calves tested positive and the positive calves and their dams were isolated immediately in a separate, empty shed a mile away from the rest of the stock. The calves were tested again 21 days later and this second positive result con­firmed their PI status. The dams were not tested again as they were antigen negative on arrival and it was assumed that the PI calves would have been the result of a transient infection (TI).

 

Control and eradication

 

Since autumn 2018, all calves are now tag tested at birth and, if any positive animals are found, they are isolated and re-tested 21 days later and culled if confirmed to be a PI. Older calves were antibody screened with check tests and the herd has moved to the Bovela® vaccine which is easier to incorporate into the herd’s management with its one-shot primary course. In addition, biosecurity has been improved and no more pregnant animals are brought onto the farm; all bought in stock is also effectively isolated.

 

Conclusion

 

The case highlights the importance of effective biosecurity, supported with sensible management and buying practice – i.e. not buying stock of unknown BVD status. The impact on the herd, in terms of calf pneumonia and also a cryptosporidiosis outbreak that was more severe than might be expected, most likely due to the immunosuppressive effect of transient BVD infection, was significant.

 

From now on, tight biosecurity, screening and vaccine protocol compliance will be implemented.

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