BHC_Newsletter_Summer FINAL

Latently infected carrier animals are almost always detectable by antibody testing and will continue to test positive for their entire life. There is no treatment that can remove latent infection from an animal. However, regular vaccination of latently infected animals can help to reduce reactivation and transmission to other cattle. A very small proportion of carrier animals may test negative for antibodies. These are called sero-negative latent carriers (SNLC). These are usually created when an animal becomes infected early in life while it still has maternally derived IBR antibodies (MDA) from colostrum. As these animals can pose a serious threat to AI stations it is important to protect young potential AI sires from IBR infection. IBR and AI Stations Semen collection centres in Ireland operate to European standards (Council Directive 88/407/ EEC) to ensure that semen produced meets requirements for trade within the European Union. These standards require that bulls entering semen collection centres are free from a range of disease-causing agents that may be spread through semen, including IBR.

The screening process for entry to semen collection centres begins with testing of bulls before they enter the quarantine facility of the collection centre. IBR is the disease which most frequently results in bulls being rejected for entry to semen collection centres. Only animals that are entirely free from IBR antibodies are allowed to enter semen collection centres. IBR antibodies may be present for the following reasons:

• Infection: the animal has been exposed to the IBR virus. • Vaccination: the animal has produced antibodies in response to an IBR vaccine.

• Colostrum: the animal received IBR antibodies through colostrum. These may persist up to 9 months of age. To avoid this, it is best practice to ensure that in the first 72 hours of life the calf only receives colostrum from a known IBR antibody-negative cow.

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