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In the last few months you may have heard experts on the COVID-19 pandemic discuss the concept of herd immunity as a way of slowing or stopping the pandemic.
It would seem that herd immunity is not an imminent possibility for the Canadian population with regard to COVID-19, but I thought it would be interesting to explore this concept to see whether it applies to our cattle herds.
One of the most important factors that affects the size of a disease outbreak when a virus or bacteria enters into a population such as a cattle herd is the proportion of susceptible individuals. For example, if a highly infectious virus such as infectious bovine rhinotracheitis virus (IBR) is introduced to a herd of cattle that has never been exposed to the virus and never been vaccinated, it will cause a very severe and serious outbreak of disease with a high proportion of the herd becoming infected.
The result in a herd of pregnant cows would be an “abortion storm,” in which a large proportion of cows abort due to the IBR virus infection. This is because the entire herd is susceptible to the virus and there is no immunity present …
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