Somerset dairy farmer James Montgomery is always quick to get on top of any disease in his farming business and a recent outbreak of BVD has been no different.
James Montgomery has always maintained a herd of the highest possible health status by keeping it closed to incoming stock, double fencing around his farm’s perimeter and even having a buffer of arable land between his own stock and his neighbours’ stock.
Such high standards of biosecurity have always paid dividends over the years as his family has developed its award-winning Montgomery’s Cheddar, which has been made on the Somerset farm since the early 1900s.
Today, the two distinct herds, comprising about 210 milking Friesians and 160 Jerseys, produce all of the milk for the entire range of Montgomery’s unpasteurised cheeses, and their high standards of health and welfare are a central plank on which the brand’s image has been built.
So, whenever there has been a rumbling of any disease in the herd, it has been stamped on and investigated in the quickest and most efficient way, ensuring there is no threat to production or quality of the end product.
This was emphatically the case in summer 2014, when the farm’s vet, Mike Kerby from the Delaware Group in Castle Cary, investigated a spate of resorptions in the Friesian herd during his routine herd health visits.
Mike says: “These were animals which had been diagnosed in-calf, but had come back bulling four to six months after service, so we immediately took bloods and tested affected animals.
“We found them to be positive for antibodies to BVD.
“This told us categorically that the BVD virus was around, which was something we had never experienced in this herd before at routine bulk milk testing.” A sequence of events was then set in train which began by repeat bulk sampling milk from the tank.
Mike continues: “The bulk sample had gone from negative to mid-positive and so gave us a conclusive result BVD had at some stage been present in the milking herd.”
At the same time, the herd’s conception rate fell from about 40% to 22%, suggesting BVD was continuing to exact its effects on the milking animals.
“Although everything pointed to BVD, we still undertook other tests, including copper and energy levels to cover all bases,” he says.
However, the evidence was overwhelming, with continuing resorptions, cows not in-calf and BVD antibodies present in milk. Mike, who explains his decision to start vaccinating with Bovela, says: “We decided to crack on and vaccinate for BVD in the first week of March.”
He says there were three key reasons for choosing this vaccine over those previously available.
“Firstly, the primary course of Bovela is just a single injection of the live double deleted vaccine, which allowed us to get the job done much more quickly, easily and effectively.”
Secondly, he says the vaccine covers both type 1 and type 2 BVD, which means both sources of infection are covered for the future.
The third advantage, Mike says, will be key to the ongoing control as a vaccinated cow will be protected for at least 12 months, both in her own right and against producing a persistently-infected (PI) calf.
“If a cow gets pregnant at any point in the 12 months following the onset of immunity after vaccination, even if challenged with BVD, she will not produce a PI calf.”
This is an important enhancement to the management of the disease in a herd, where a PI calf, which can be formed when a cow is infected with BVD in her first four months of pregnancy, can wreak havoc by providing a constant source of infection, shedding the virus and infecting other animals.
Mike explains: “Cattle which are infected with BVD after birth are transiently infected and will normally recover in about four weeks. But a PI calf will have the virus all of its life and spread it in huge quantities at various times, so preventing PIs is an important part of the strategy.”
With the entire herd of black and whites now vaccinated, Mike says the campaign to find the source of the viral infection and eliminate BVD from the herd continues.
He says: “This involves testing the bulk tank again for the virus itself which has now been done and has come back negative. So, the cows giving milk on that day did not carry the virus. “The next step is to test the milk again in three months’ time, then repeat this again, until eventually, all milking animals have been tested.”
The alternative, Mike says, is to blood test every animal, including youngstock, until eventually the offending animals are found.
“Blood testing may be the ideal and quickest approach, but by testing milk for the virus every three months, we will eventually pin it down.” For the time being, he says, the source of infection remains a mystery and a PI animal has yet to be found.
“Our current thinking is the virus must have got into the black and white adult herd, possibly through an incursion of a transiently infected neighbouring animal.”
A further important step will now be to ‘tissue tag’ calves, allowing any PI newborn to be identified at the earliest stage and removed from the herd. Emphasising the importance of driving out the infection from the herd altogether, Mike says BVD has by far the highest cost to the farmer of all infectious diseases.
He says: “Every producer should know his herd’s status and consider taking action if infection is present.
“The hidden costs are huge, not just through effects on reproduction, but also because of its immuno-suppressive effects, which leave infected animals, especially youngstock, vulnerable to many other diseases.
Allan Henderson, cattle business manager at Boehringer Ingelheim, says: “BVD is one of the most common viral diseases affecting cattle throughout Europe, despite vaccines being available for more than 50 years.
“It can cause early embryonic death and irregular returns. Later in pregnancy, it can cause foetal mummification and abortion. Work has shown it may also contribute to cows either failing or taking longer to conceive.
“BVD can affect unborn calves at any time during pregnancy with varying degrees of severity. The most sinister presentation is the persistently infected [PI] calf which looks healthy, but is producing massive amounts of virus and infecting all cattle with which it has contact. “Bovela is the first and only vaccine in the UK which has been proven to protect cattle from BVD type 1 and 2,” adds Mr Henderson.
“Bovela is a unique one-shot vaccine which can be used in breeding females and in calves from three months of age. Control of BVD depends on understanding farm BVD status, identification and removal of PIs, biosecurity and ongoing monitoring, as well as vaccination.
“Seeking veterinary advice on how to best tackle BVD in your herd is the best starting point,” says Mr Henderson.