BVD (Bovine Diarrhoea Disease) has been talked about now for many years, but we are still finding infected herds are common, both for dairy and even more so for beef.
The consequences that follow infection are varied. In young cattle less than 12 months, BVD suppresses their immune system and makes them more susceptible to other health problems like scouring, poor growth, coughing, ulcers in the mouth, and lameness. This means it takes longer to get to appropriate liveweights, and the cost of treatment starts to increase.
When infection enters a milking herd a significant drop in milk production can occur over a three-week period.
If the timing of this infection is around mating, both beef and dairy cows will have higher empty rates and later calving cows than expected. Infected bulls will have a lower fertility.
Diagnosing BVD in calves
For dairy herds, picking up calves that are persistently infected is key to eliminating infection cost effectively. Calves become persistently infected when cows are infected during their pregnancy.
Increasingly in dairy herds, the testing of calves for persistent infection is a routine procedure. Both the ELISA and PCR tests can be used in young calves to detect the virus. These are both highly accurate and will detect almost 100% of persistently infected animals with a single test. Our preference in calves is to use the PCR test on ear notch or blood samples. In beef systems the blood sample around weaning or premating is often easiest to manage logistically.
This is because using the ELISA test on blood samples taken from very young calves (less than 35 days of age) can result in false negatives where a PI calf has been feed colostrum high in maternal BVD antibodies. In this circumstance, the maternal antibodies bind most of the BVD virus particles and prevent the test components from working correctly.
Calves can be tested for BVD almost immediately after birth and many farmers find it convenient to collect ear notch samples on their replacement heifers at the same time as placing the NAIT tag or performing disbudding. Once an animal has tested negative for BVD virus, it can be certified as non-PI for life and does not need to be tested again.
As you start thinking about which heifer calves you are going to keep this season, please talk to one of our vets or techs about how BVD calf testing fits into your animal health programme.