Are Southern Deer Genetically More EHD Resistant?
by Charles “Deer Man” Black
Whitetail Rack Ranch
I keep seeing ads about 'buy my deer because they are EHD resistant southern deer'. Everyone can have an opinion on something but when it's controversial sometimes people get a little overzealous in their arguments. I'm a scientist, not a mad scientist, and not one in a lab with bubbling bottles but I have a Bachelor of Science degree as a wildlife biologist and studied deer behavior for two master’s degrees. That doesn't make me smarter than anyone else but that much education does cause your mind look at things a little differently and helps in understanding scientific data.
For this article, EHDV stands for Epizootic Hemorrhagic Disease Virus and BTV stands for Blue Tongue Virus.
In a scientific study, all variables not being manipulated for research should be controlled. For example, if I had two groups of deer in my study to determine if protein supplements produced bigger antlers and one group was my 'control' that didn't receive the supplement but they had a food plot with high protein beans and the group that received the supplement had Bermuda grass, then it wouldn't be a good scientific study because the variables in the food plot would make the study inaccurate.
A lot of what you hear about deer health and what works is anecdotal evidence. Anecdotal evidence is not scientific in nature. For example, if I put vanilla extract in my deer water and they never got EHDV/BTV then vanilla being a prevention for the viruses would be anecdotal evidence. They may go one or several years without getting the viruses without any treatment. It doesn’t prove that vanilla extract helps with virus prevention. The study would have to be set up within the strict guidelines of a scientific study to yield reliable results.
The 'Facts' that you hear about EHD resistance in deer is often anecdotal. You may have heard someone say, “I bought some northern deer and put them in pens with my southern deer. When EHD hit, most of my losses were the northern ones. That proves that my southern deer are genetically superior to northern ones for EHD resistance.” They have no true evidence to back that up. I hope that I can clear up some myths about EHDV/BTV resistance by giving factual evidence from scientific research.
Research was conducted at the University of Georgia (Gaydos et. al., 2002) to determine the influence maternal antibodies have in resistance to hemorrhagic diseases in white-tailed deer. Twelve Texas fawns were moved from an outdoor facility in TX to an indoor facility at the University of Georgia. All of the fawns tested positive for EHD/BT antibodies which means they had resistance. EHD and BT have different serotypes, like ‘strains’ of flu. The tests were positive if antibodies were present for any of the serotypes. It’s highly unlikely that antibodies would be present for all serotypes. At 18 weeks of age they no longer tested positive for the antibodies. There were 40 fawns remaining at the TX outdoor facility ranging in age from 14 to 21 weeks of age that were also tested. They found that 98% in the outdoor facility still had antibodies to EHD and/or BT. The study concluded that there was strong evidence showing the fawns in the indoor facility had initial antibodies from passive influence from the mothers. Evidence showed the fawns raised outdoors in TX with the initial passive immunity from the mothers allowed the fawns to survive exposure to the virus and build their own immunity. The fawns at the indoor facility in GA had no such exposure and therefore lost antibodies after the passive immunity from their mothers had declined. These fawns came from the same group in Texas. The only difference was exposure or no exposure. If the theory that TX deer are genetically resistant to the viruses was true, then they should still have shown antibodies when tested.
A much earlier study (Hoff et. al, 1974) was conducted in Texas in an area of prevalent BTV from 1963 to 1972. When tested, the neonatal fawns (birth to 2 weeks of age) had 93% that were positive for antibodies for BT, only 36% of juveniles were positive and 89% of adults were positive. Antibodies decreased from birth to 12 months of age but increased after 12 months of age. Again, this shows that fawns from mothers that have antibodies get passive resistance but lose the passive resistance after a couple of months and begin to build their own immunity. The juveniles’ positive response for antibodies ranged from a low of 0% in some years to 77% in another year. No response would indicate they never had exposure after the passive immunity had diminished.
The fluctuation in antibody presence in the juveniles is consistent with my theory that regardless of northern vs. southern, deer must have exposure to build immunity. The cyclic nature of EHDV and BTV would produce naïve young animals in some years. If a severe outbreak doesn’t occur for 3 years, all of those deer up to 2 years of age are highly susceptible to the viruses.
If it were true that southern deer were genetically immune to the EHD/BT viruses, then age after passive immunity and conditions of exposure or non-exposure shouldn’t matter. These studies show that southern deer from Texas lose immunity without exposure. Passive immunity is derived through the placenta or through the immunoglobins in the colostrum of the mother’s milk. Semen does not contribute to passive immunity. There are areas in the South where EHD/BT viruses seem to occur with less severity. More likely, it’s in an area where exposure is common from year to year. Fawns may get the virus but their passive immunity allows them to better handle the disease when they are exposed as fawns and the exposure builds their own immunity. Symptoms may be subclinical (symptoms aren’t obvious) if they have passive immunity as fawns. This may lead one to believe that their deer never get the virus when they actually must get it to produce their own antibodies.
If the animals were EHD resistant because they were from the south and it was in their genetics, then the EHD antibodies would have been there after weaning for both groups. The argument that if you buy northern deer and move them to the south, they won't survive isn’t true. I’ve raised hundreds of pure northern genetics deer in Louisiana. Did I lose many when I moved them here? You bet. I got sick of going out and dragging dead deer out of the pens. The southern resistance guys will say that mine died because they weren't EHD resistant or weren't used to our insects or other diseases. I agree in part, but.....when deer are handled, they are stressed. If they are darted they are stressed even more. A study in South America on red deer showed lack of immune response 30-40 days after tranquilization. Hauling deer in a trailer for 20+ hours adds to the stress level they already have. Then you dump them out in foreign surroundings often mixed with deer that start pecking order fights. They are put abruptly on new feed. It's no wonder so many die. And stress doesn't just last 2-4 weeks. Some studies indicate that stress related illnesses can occur up to a year later. I learned to greatly diminish death losses of northern deer that have been newly translocated to the South and have had much better success.
Another study by the University of Georgia (Gaydos et al., 2002) was conducted to determine if there is an advantageous innate resistance to EHD in southern deer compared to northern ones. Fawns were chosen from Pennsylvania and Texas. The fawns were moved to an indoor facility in Georgia by 2 weeks of age. The fawns were tested for antibodies to EHDV/BTV. The PA fawns tested negative for antibodies while the TX fawns tested positive for antibodies.
Five fawns from each group were experimentally infected with the virus. All 5 from the PA group died from the viruses and all 5 of the TX fawns survived even though the TX fawns did become infected. The researchers acknowledged that they failed to prove that the TX group was innately more resistant but stated that the study does indicate that animals from some areas have better resistance than animals in other areas. This research suggests that the fawns brought from PA didn’t have resistance and didn’t survive because they came from an area that didn’t provide exposure to the viruses. The PA fawns were at a disadvantage, not because of their genetics, but because they had no immune response because they hadn’t been exposed nor had their mothers in PA.
The mistake people make is interpreting the results to mean that Texas deer are genetically more resistant to EHDV/BTV. Another study should be done by taking pure northern animals that have been in the south for several generations and comparing them to the native southern animals in the same pen.
Northern deer moved to the South will likely be low in resistance. Since EHDV/BTV is cyclic, a naïve deer (one that has never been exposed) may need several years to gain enough exposure to build immunity. That’s where northern deer get a bad reputation. They typically have a higher death rate those first few years.
I believe that moving northern deer south will result in some deaths. Minimizing stress through proper handling will increase survival rates. Bringing feed from their place of origin and gradually changing the ratio of new/old feed will be less stressful. Pen size changes can cause stress as well as being introduced to new animals. Your veterinarian can recommend a prophylactic antibiotic program for prevention of early disease problems like shipping fever in cattle after moving. Anything to mitigate the changes and stress that results from it will increase survival rates.
As for EHD, I believe that northern deer can survive very well in the south. They must have some exposure to the virus. There will be deaths at first. But, I know of many pure southern deer that have died from EHD. Ask a biologist from any southern state when there is a bad epidemic of EHD or BT. Native deer are dying in the woods. Louisiana State University has southern white-tailed deer in their research facility that die in large numbers during severe EHD/BT virus outbreaks. One of my customers in Louisiana does a controlled burn on his hunting property every year and has 100% southern deer. He said it’s incredible how many skeletons he finds after a bad EHD/BT year when the undergrowth has been burned away and exposed all the deer that had died. I have another Louisiana customer that is very happy with his 100% big-bodied northern bucks that I sold him for breeders in his hunt pen (see photo). They have those big, heavy, massive northern antlers. The bucks have been in his hunt pen for two breeding seasons next to crawfish and rice ponds and swamps that are ideal for raising the midges that cause EHD. The bucks will be six years old this year. They were born and raised at my ranch in Louisiana. They lived through some very bad EHD years.
If you move northern deer south, just prepare for higher death rates. Once they get past that first year they do much better. The offspring in future generations don't know the difference. The advantages of northern bloodlines are worth what we went through initially. If you don't want that heartache and stress, buy northern bloodlines from someone who has suffered through it and has the strongest survivors. Buying northern genetics has its risks but there are also many advantages that they can add to your program. Why would so many Texas ranches have northern influence if it caused their deer to die from EHD? The semen from northern bucks isn’t diluting the antibodies in the northern-cross offspring because the fawns only get the initial passive immunity from their mother.
EHD and BT viruses are killers no matter where the deer are from when outbreaks are severe. Texas has some great deer. There is absolutely nothing wrong with including their genetics in your program. But you’ll be disappointed if you think you will get EHDV/BTV resistance from using their semen. If you buy a 100% Texas doe and bring her to Minnesota, she may have permanent immunity to one or more of the serotypes because of her past exposure. The best that she can offer her offspring is a couple of months of passive immunity when they are born. By late summer the passive immunity begins to rapidly diminish so they will still very likely get EHDV/BTV if they are exposed later in life.
By all means use Texas genetics if they have the physical traits you desire. Likewise, don’t be afraid to use northern genetics in the South for the same reason. Just remember to look at the science and not the hype if you are considering breeding a certain way because you think it will guarantee EHDV/BTV resistance.
Gaydos, Joseph K., David E. Stallknecht, Darrell Kavanaugh, Robert J. Olson, and Eugene R. Fuchs. 2002. Dynamics of Maternal Antibodies to Hemorrhagic Disease Viruses (Reoviridae: Orbivirus) in White-tailed Deer. Journal of Wildlife Diseases 38(2): pp. 253-257.Hoff, G. L., D. O. Trainer, and M. M. Jochim. 1974. Bluetongue virus and white-tailed deer in an enzootic area of Texas. Journal of Wildlife Diseases 10: 158-163.
Gaydos, Joseph K., David E. Stallknecht, Darrell Kavanaugh, Robert J. Olson, and Eugene R. Fuchs. 2002. Innate Resistance to Epizootic Hemorrhagic Disease in White-tailed Deer. Journal of Wildlife Diseases 38(4): pp. 713-719.