Wednesday, November 30, 2011

EHD: Northern vs. Southern Deer Resistance

I had a conversation with a friend about northern vs. southern EHD resistance. I wanted to share some of my thoughts. From the research I've read, I don't believe northerns with exposure to EHD will have any more trouble than southerns if their previous exposure history is the same. I hear it all the time that northerns aren't EHD resistant but I think that the people that have southerns are the ones promoting that view. If you bring northerns down south they likely won't have the resistance of deer born and raised in the south. I know someone in southern Louisiana who has said for years that it was a mistake to have northerns in the south. I haven't heard him say much since he lost a bunch of his southerns a few years ago when I was losing northerns. Even with southerns, research shows that fawns lose their immunity after weaning if they don't have continued exposure to the virus. It takes time for northerns to build their immunity because of the cyclic nature of EHD. If you bring northerns down and there is no significant EHD present for a few years, when it hits hard I would expect northerns to have somewhat higher death losses. Likewise, though, if fawns lose their immunity without having contact with the virus wouldn't the southern ones have higher death losses later in life too? I personally believe we're going to see EHD worsen for southerns in the future. If someone puts up a mister system around their pens, they eliminate the chance for building immunity to the virus. Animals MUST be exposed and get the virus to have immunity. One thing that you may be seeing in your southerns with flu-like symptoms, rather than more severe symptoms with northerns, is their history. Research shows if a deer gets EHD-1 it will have SOME cross protection but NOT immunity to EHD-2. Once the animal has the virus it should have lifetime immunity for that particular serotype. That's why live virus vaccines are only given once without the need for annual boosters as compared to killed virus vaccines. The problems facing us with EHDV and BTV is similar to humans and the flu. Mutations each year present the animals with slightly different viruses. The permanent immunity to one serotype doesn't prevent infection from a different one. Give northerns in the south some time to build their immunity and lets hope mister systems don't cause our southerns to lose their resistance. Something else I hear people promote is buying semen from their EHD resistant southern bucks. I have seen NO evidence of EHD protection passed down from the sire. Think about it just from a common sense perspective. Why do we vaccinate for BRSV, BVD, IBR, PI3, C&D, etc. if there is passdown immunity from the mother. We should be able to vaccinate a doe and all of her offspring would have immunity without ever needing to be vaccinated. Immunity doesn't work that way!!! Feel free to comment.

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