BVD Impacts
How well would your business survive with an empty rate of 60% this season? BVD outbreaks can have devastating impacts on herd health and performance especially if the virus gets into the wrong cattle at the wrong time of year.
What impacts does BVD have on non-pregnant cattle?
Increased disease in calves
When calves < 12 months old become acutely infected with BVD, it suppresses their immune system and makes them more susceptible to other health problems like scouring, poor growth, coughing, ulcers in the mouth, and lameness. These calves may require additional veterinary treatment and additional time to reach appropriate weaning weights.
Decreased milk production
When lactating cows become infected, they may have reduced feed and water intake for up to 3 weeks, which can cause a significant drop in milk production levels. This can have an effect on total yields for dairy cows as well as impact the growth rates of suckling beef calves.
Poor conception rates
Infections during the mating period can cause damage to the eggs and create a poor uterine environment, which results in a failure to conceive. Sick animals may also display fewer visible signs of oestrus.
Reduced bull fertility
Transiently infected bulls can have poor semen quality due to the combined effects of virus and the presence of BVD in the semen leading to fewer cows getting pregnant. They may also be more susceptible to other diseases.
What impacts does BVD have on pregnant cattle?
Early embryonic death
Even if fertilization occurs, the resulting embryo may not be viable leading to early embryonic death and long returns (25 to 35 days) to service in herds that are using artificial insemination.
Abortions, mummies, and stillbirths
If the virus does too much damage to the calf up to 180 days into pregnancy, it can be fatal and result in an abortion. The immunosuppression caused by BVD may also trigger abortions from Neospora or fungal agents. Mummified fetuses and stillbirths can also occur if the fetus is not expelled from the uterus after death.
Persistently infected calves
If the fetus is exposed to BVD from 40 to 120 days into pregnancy, the calf may be born with a persistent infection (PI). These calves shed virus for life. They are often stunted and grow poorly with many dying or being culled from the herd before reaching 12 months of age. If the strain infected a PI animal evolves into a more severe form of BVD then this can develop into fatal mucosal disease in these PI animals.
Developmental defects
If the pregnant cow is infected from days 90 to 150 days into pregnancy, the calf may be born with severe developmental defects that result in early death or that require humane euthanasia.
Weak or stunted calves
If the pregnant cow is infected greater than 180 into pregnancy, there is a chance that the calf may be born small or weak. These calves have poor growth rates and reduced fertility due to the damage that BVD can cause by replicating in ovarian tissue.
Impacts of BVD infections in late pregnancy on growth performance
BVD infections during late pregnancy can damage the developing calf and affect its ability to grow at a normal rate after birth. The two heifers shown below were born during the same week. The heifer on the right was infected with BVD during late pregnancy and never managed to catch up with her herd mates.
Normal Heifer - 222 kg
Affected Heifer - 75 kg
How much does BVD cost infected herds?
The impacts of a PI animal getting into your herd will depend on a number of factors including:
Herd Type – Beef versus Dairy
Type of PI Animal – adult replacement versus newborn calf
Timing of Introduction - When the PI animal was introduced relative to the mating period
Levels of Herd immunity - against BVD from either vaccination or previous BVD infections
Contact Rates - The amount of direct or indirect contact the PI animal has with pregnant cattle in your herd
If PI animals are introduced around the time of mating, you are most likely to see high returns to service for AI mating and high empty rates due to transiently infected animals having difficulty getting pregnant and maintaining the early pregnancy. The time window where you have pregnant cattle that are risk of creating PI calves if they get transiently infected can last over 6 months depending on the length of your mating period. Abortions can happen throughout the pregnancy period, which may show up as abortion storms or fewer calves born the following season that you were expecting.
If a lot of your cows were transiently infected later in the season, you may notice calves that have birth defects like cleft palates, abnormally large heads (hydrocephalus), or misshapen eyes. Affected calves may also be much smaller than others in the herd and struggle to catch up in growth leading to uneven slaughter weights and fewer heifers reaching target body weights by mating. BVD outbreaks in your calves may also result in more episodes of diarrhoea and respiratory illness.
BVD outbreaks tend to be most severe in the first year and then less noticeable in the following years as more of the herd gets immunity against the virus. However, infected herds often still experience significant effects on reproductive performance and calf health. Furthermore, as long as there are PI animals in your herd, you are risk of causing other farmers to have outbreaks in their herds.
Check your understanding
Answer the questions below to check how well you understand the basics of BVD Impacts
Check Answer
The correct answer is (d).
Birth defects will only occur if the animal is infected as a fetus during late pregnancy (days 120 to 280).
Check Answer
The correct answer is (c).
If the herd experiences a BVD outbreak when dams are in late pregnancy, you may see a lot of stillborn calves, weak calves, calves with birth defects, and calves with stunted growth.
Check Answer
The correct answer is (a).
The impacts of a BVD outbreak will depend on the existing level of herd immunity against BVD as well as the timing of the introduction. The most severe outbreaks will occur when a PI animal is introduced to a completely susceptible herd around the start of the mating period.
Check Answer
The correct answer is (a).
Based on the latest estimate from the BVD Free economic modelling, a BVD outbreak in a naive herd is expected to cost around $22 per cow per year for as average dairy herd and $41 per cow per year for an average beef herd over a 5 year period.
Check Answer
The correct answer is (b).
BVD has an impact on every single cattle herd in New Zealand. Many herds that are negative for BVD have high ongoing costs from vaccinating susceptible dams and testing purchased cattle to prevent BVD from being introduced into the herd.