Bovine Viral Diarrhoea (BVD) is a highly contagious disease that costs the beef and dairy industries more than £33 million a year.
What is BVD?
The virus itself is closely related to Border Disease in sheep and Classical Swine fever in pigs. How BVD affects the herd varies. Adults show signs of fever, lethargy, decreased milk production and diarrhoea. Foetal infection in utero can lead to abortions, congenitally deformed calves that are weak and sometimes die, to persistently infected (PI) animals. Due to the immunosuppressant nature of the disease, infected animals are more susceptible to other diseases like pneumonia and scour and links have been made to an increase in cases of TB in an infected herd. The biggest issue is the impact BVD has on reproduction. Infertility, foetal absorption, mummification of the foetus, congenital defects of the eyes and nervous system and weak and premature calves are all markers of BVD. The virus is perpetuated within the herd by animals that are Persistently Infected (PI) with BVD. If cows or heifers become infected within the first 120 days of pregnancy, and she doesn’t abort the calf, it can be born with the disease and will be a Persistently Infected animal. If the dam becomes infected early in the gestation period (before day 110) the underdeveloped immune system of the unborn calf doesn’t recognise the virus as foreign. The animal incorporates it into its immune system and sheds the virus for life. Once born, these calves often show no signs of the disease but become super-shedders. They shed millions of virus particles in their skin, saliva, urine and faeces which then spreads rapidly throughout the herd. A single PI in a calf pen can spread disease to the rest of the herd. The damage a PI can cause could end up costing farmers a fortune in infertility issues, high abortion rates, loss of productivity, outbreaks of scour and pneumonia. Some of the PI youngsters can develop Mucosal Disease, resulting in fevers, ulceration of the nose, mouth and feet, severe diarrhoea and eventually death. Some PI animals go on to become breeding cows but will always give birth to a PI calf perpetuating infection in a herd.
How is it Spread?
If you already have a PI in your herd, the virus can be spread by nose-to-nose contact, saliva, urine, faeces etc. The disease is maintained within a herd by a PI. There are tests available that can help identify a PI or an infected animal. Bought-in animals are also one of the biggest risks. They can be PIs or simply infected, causing the disease to spread within your existing herd. Contact with neighbouring cattle across fences is a biosecurity risk, as well as contact through markets and a shared or hired bull. An infected bull can spread the disease through its semen.
The ADAM acronym sets out the four steps that will help you achieve a BVD free status.
A – Assess your herd for PIs and disease risk, including the environment your herd is kept in, neighbouring cattle etc., anywhere that your cattle could come into contact with the disease.
D – Define the status of your herd with testing.
A – Action Create and implement an action plan for the control of BVD on your farm.
M – Monitor your herd, revisit steps 1 and 2 regularly to ensure your cattle stay BVD free.
Essential to control is making sure you identify and cull any PIs in your herd and then follow up with testing replacement animals and vaccination for the remaining animals. We can help you identify the PIs and can advise on various vaccine options. As more herds become clear of infection, the risks of infection reduce. If you have any concerns, give us a call.