1. Epidemiology

What is BVD?

2. Transmission

How can BVD get into my herd?

3. Impacts

How does BVD impact herd health?

4. Diagnostics

How do I know if my herd has BVD?

5. Control

How do I control BVD in my herd?

6. Eradication

How can national eradication help?

3. Impacts

 

BVD can have significant effects on animal health, welfare, and productivity depending on the age, pregnancy status, and production type of the infected animal.  The economic consequences of a BVD outbreak in your herd will depend on how and when the virus was introduced as well as how quickly it spreads between cattle.  The worst-case scenario would be buying in a persistently infected (PI) bull or PI replacement dams and mixing them directly with the main breeding mob after the planned start of mating. This has the greatest potential for causing significant reproductive losses leading to high empty rates.

Animal Level Impacts

  • 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.

  • Reduced 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.

  • 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 foetuses and stilbirths can also occur if the foetus is not expelled from the uterus after death.

  • Persistently infected calves

If the foetus 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.

Herd Level Impacts

When you scale up the effects of BVD on individual animals to the herd level, it can end up being a costly disease for beef and dairy farmers.  There have been a few studies in New Zealand looking to estimate the cost of BVD in dairy herds.

1. The first study (Weir et al, unpublished) looked at the impact of transient infections occurring between the start of mating and autumn.  The conservative estimates of costs based strictly on reproductive performance and additional disease treatments was ~$110 per cow.

 

Factor

Effect

Value

Calving to conception

6.6 days later

$54.48

Conception to AI

11% less

$8.58

Pregnancy rate

3.1% lower

$32.24

Disease treatments

 

$13.67

 

Total

$108.97

* $6.50kg, 1.2kg/d, $120 premium for AB calf, $800 premium for pregnant cow

2. The second study by Heuer and colleagues found that actively infected dairy herds had:

  • 5% lower daily milk production
  • 2.4% later conception with a further 1% milk loss
  • 2% higher abortion rate
  • Greater incidence of mastitis

The estimate of cost from this study was ~$180 per cow or up to $150 million annually for the entire cattle industry.

The third study (Voges, unpublished) looked at the costs of persistently infected (PI) cattle and found that they had:

  • 23% higher risk of clinical mastitis
  • 22% higher risk of severe illness or sudden death
  • 18% slower growth rates
  • 23% lower milk production
  • 6% higher abortion rates
  • 17% higher mortality up to 2 years of age

All of these studies likely underestimate the true economic cost of BVD for dairy herds because of relatively limited number of factors included in the economic models.  Furthermore, much less is known about the economic impacts of BVD in New Zealand beef herds.   One previous study on reproductive performance in low and high fertility herds estimated that the pregnancy rates were anywhere from 5% to 15% lower in BVD infected herds.  Assuming a 5% loss of weaners at $400 per head and replacing 5% extra empty cows at $200 per head, we would expect the average cost of BVD to be around $3,000 per 100 cows per year.  This does not account for additional costs such as wider calving spreads, poor growth rates of calves, increased calf mortality, and additional treatment of calves for secondary infections.  As part of our SFF research programme, we will be collecting more data from beef and dairy herds to generate better estimates of the cost to individual farmers and to industry. 

Industry Level Impacts

There are many externalities to BVD besides just the direct economic impacts on individual farms.  Having calves born weak or with birth defects is an animal welfare issue that a creates a negative image for the beef and dairy industries.  BVD also increases the susceptibility of infected animals to other infectious diseases, which often require additional antibiotics to treat and increases the overall use of antibiotics in New Zealand.  Because BVD decreases the reproductive efficiency and milk yields of cattle herds, it means that it takes more resources to produce the same amount of dairy and beef products, which increases the environmental impact of the cattle industries.  Furthermore, with an increasing number of countries establishing national BVD eradication programmes, it is likely that New Zealand’s BVD status will also have an impact on international trade in the future.