Most of you will have heard of BVD (Bovine Virus Diarrhoea), the complicated viral disease of cattle that causes big financial losses in commercial dairy and beef herds across New Zealand. A recent estimate for the dairy industry was a loss each year of $37 million, and about 90% of dairy farms are thought to have had the virus at some time.
BVD maybe isn't having much impact on most lifestyle farms but it's hard to tell because although it's certain to be present on many small farms it can be difficult to recognise.
Recent infections are picked up from other cattle, and in cows, the effect is mainly on the reproductive system:
- Poor conception rates
- Embryonic loss
- Returns to service
- Increased calving spread
- Dummy calves and birth defects
In bulls, recent infection may cause temporary infertility.
In calves, the signs are rather different:
- Ulcers in the mouth
- Weight loss
- Eye and nose discharge
- Immunosuppression (leading to pneumonia, lice, worms and mastitis)
To complicate things further, there is another form of the disease. Calves can become infected in the womb if their dam picks up the virus in the first half of her pregnancy. The calves look normal for a year or two but they are persistently infected (PI), and they excrete the virus throughout their lives. Well before they reach 2 years of age, most of them develop severe diarrhoea and die.
If you are concerned, speak to your vet about it. He or she might arrange blood tests to tell if your cattle are PI or if they have been exposed to the virus.
Vaccination can be used as a method of control. In commercial herds, it's sometimes used in conjunction with a test and eradication programme for PI animals.