BVD is an expensive viral disease of cattle. In New Zealand, active BVD infection costs:

$70,000 / 400 dairy cows/year & $3,500/100 beef cattle/year

BVD stands for “bovine viral diarrhoea.”

HOW DOES BVD WORKS:

Naïve animal:

• Has never been exposed to BVD
• If you test a naïve animal or group of animals, you will find no BVD antibodies or BVD virus in their blood, milk or body tissues

Transiently infected animal (TI):

• Has just been exposed to BVD for the first time – gets sick for 2-3 weeks
• Signs of transient infection include: pneumonia, diarrhoea, milk drop, high somatic cell count, pregnancy loss, abnormal calves, immune suppression
• If you test a TI, you will find low levels of BVD virus in blood & milk
• Transient infections are where the main costs associated with BVD are incurred; each transient infection occurring during mating costs approx. $90
• TI cattle don’t excrete much virus, so ARE NOT the major source of BVD spreading through a herd

BVD Immune cow:

• Has been transiently infected at some time in the past
• If you test an immune cow or group of immune cows, you will find no BVD virus, but will find BVD antibodies in their blood and milk

Persistently infected animal (PI):

• The main source of BVD – contact with PIs are the main way naïve animals become transiently infected
• PI cattle shed high levels of the virus in their body fluids for their entire lives
• PIs form when naïve cows are exposed to BVD when they are 40-150 days pregnant: the cow becomes immune to BVD but the fetus can become a PIÐso PIs are born PIs and die PIs
• If you test a PI, you will find lots of BVD virus in their blood, milk and skin, but no BVD antibodies

WHY IT’S IMPORTANT TO ACTIVELY CONTROL BVD:

• BVD spread from PI animals to naïve animals is not predictable
• If left alone, a herd containing a PI nearly always continues to have naïve animals in it, which continue to be at risk of getting sick (and continue to cost you money!)
• It is most cost effective to put active BVD control measures in place:
  • Find and eliminate PIs
  • Prevent new PIs from being created
    • Biosecurity
    • Vaccination (protects the fetus)

REFERENCES

1. Heuer C, Healy A, Zerbini C. (2007). Economic effect of exposure to bovine viral diarrhoea virus on dairy herds in New Zealand. Journal of Dairy Science. 90:5428-38.
2. Heuer, C et al. (2008). Effect of reproductive pathogens on pregnancy rates in beef herds. Proc. 38th Seminar of the society of sheep and beef cattle vets of the NZVA: 141-147.
3. Hansen et al. (2015). Innate and adaptive immune responses to in utero infection with bovine viral diarrhoea virus. Anim Health Res Rev. 16(1):15-26.
4. Lindberg, A. & Houe, E. (2005). Characteristics in the epidemiology of bovine viral diarrhoea virus of relevance to control. Preventive Veterinary Medicine.72:55-73.
5. Weir, A. (2015). BVD Simulation Model. Dairy NZ Roadshow.
6. Reichel et al. (2008). Does control of bovine viral diarrhoea infection make economic sense? N Z Vet J. 56(2):60-6.
7. Reichel et al. (2018). Perspectives on Current Challenges and Opportunities for Bovine Viral Diarrhoea Virus Eradication in Australia and New Zealand. MDPI Pathogens Review.

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