Moving Forward- Breeding for Resistance to Marek's Disease

[seminolewind]

Thanks Chooks.

Because it's possible in Florida, I've moved all my chickens to covered outdoor pens mostly for lessening Aspergillus concentration.
I agree, vaccination is not as good as resistance. And there are breeders who take this into consideration when picking out their breeders.
But it's not enough. So the only way to not have mass deaths is to vaccinate. On top of that, I will not share any birds from my flock.
There's still the problem with vaccination masking exposure.

Where the heck is Nambroth? She is as obsessive as we are about Marek's information?

Cynthia, this stuff can make us all crazy. But it still does not look like you have Marek's in your flock.

EYP is the most common death in hens. Apparently caused by the vent and cloaca being close together, and the enlargement of the cloaca with good layers making it easy for e.coli infection to spread all the way up to the ovary. I may have had less problems with that because most of my hens are Polish or not known to be great egg layers.

 

[speckledhen]

Quote: My theory is that when it happens with a young hen, she may have a defect that allows feces to be sucked back into the oviduct, whereas, with an older hen, the cloaca can become "loose" over time. That's the only explanation for my last loss.

 

[gjensen]

This is an interesting thread. It has a lot of interesting theories and ideas.

The conclusion that I came to is that breeding for resistance is not as clear cut as it sounds. Truly breeding for resistance involves intentional exposure (repeatedly) over generations. The pathogen would have to be the same strain etc. Then it would be necessary to test mate and "prove" the breeders. After all of that, you would find that often those that showed some tolerance and did not become symptomatic, would not pass the trait on to it's offspring. It has been found that a bird that did become symptomatic could possibly pass the ability to resist (tolerate), to the offspring.
Truly breeding for resistance requires a controlled setting, many generations, access to the pathogen, and test mating. This is not to say that a breed (or strain) would not be better off in the long run for this approach. I do think it is helpful to keep it in perspective. It is not as simple as some make it sound.
Generationally from one breeder to another, in a given area, real progress could be made. All bets are off when the bird is shipped across the country and is exposed to a different strain.

Instead I prefer to select for health and vigor. A healthy and vigorous bird is less likely to succumb to less virulent strains and low level exposure. A less vigorous bird may succumb sooner. Also culling a symptomatic bird limits the flock's exposure, which I believe is an important management tool. I would not want any problematic pathogen replicating itself over time in my yard. It is possible to get stuck contending with something seasonally year after year.

Where I ended up concerning Marek's is for as long as I do not have any substantial losses, I will manage my birds as I do. If they are ever exposed to an especially virulent strain, after culling symptomatic birds, I would start vaccinating. I have been fortunate up to this point, so I do vaccinate. If that changed, I would change. Mareks has the potential to be devastating.

 

[Nambroth]

Cynthia, I would think if your hen at anything to do with Marek's , she would have tumors-lots of them-enough to be on a necropsy. (Right , Nambroth?)

Sorry, this Duck Stamp thing has completely consumed my life. I never imagined I'd ever be so busy!

My answer, as a non-expert, is a solid MAYBE....
Viceral nerolymphatosis, which is a fancy way of saying "the Bad Marek's", is going to nearly always present with tumors and some level of ataxia, unless the bird is put down before the nervous system is "attacked". Tumor growth is often rapid. One of my roosters had a very small thymus tumor, and within two weeks was dead. He demonstrated paralysis approximately four days after the initial tiny tumor was found, and was struggling to breathe the next day. It does not always progress this rapidly, but it is not unusual for it to do so, either.
All of that said, I would expect Cynthia to see something more-- some sign that leans more toward Marek's, if she is having a problem with it in her flock. Especially given how closely she pays attention to her birds!

As this thread has explored, though, Marek's does not always play by the rules that we understand.

Regarding the reference to Chicken Pox, the idea is somewhat similar. It is a herpesvirus and it replicates itself in the hosts' cells via replicating DNA. In this way, much like Chicken Pox (of humans), after an individual has been infected, the immune system might fight it off and the individual recovers. Later, during an event of immunosupression, such as stress, other disease, etc... the individual can have reoccurring symptoms (in humans, Chicken Pox likes to come back as what we know as 'shingles').
The Herpes we know of in humans is probably a better example of how the virus stays latent in the person's body and 'shows itself' again as reoccurring symptoms, MOST ESPECIALLY during times of stress, poor health, complications of other illness, etc.

Cynthia's idea of "happy, healthy, stress-free (as possible) chickens" as being the strongest, in general, seems like a very good goal for anyone keeping chickens.


That said, there are just so many factors. Genetics, exposure to which strains?, general immune health of an individual, climate, breed (genetics at play again), etc... all seem to factor in. It is complicated. It sucks.

 

[seminolewind]

Sounds like gjensen and Nambroth explain this much better. There are so many if's and's or butt's in Marek's, it's hard to pinpoint solid symptoms or methods to induce resistance. There are so so many factors considered for resistance , and possible false negatives as well. Stress can be a factor? Is missing a meal stress?

I would still like to look into trying exposure during the first 2 weeks and then removal of the chick for 2-4 months. I don't know how long to expose the chicks, but it might be a good way for backyard owners that have no access to a lab.

 

[speckledhen]

Quote:

 

[gjensen]

Sounds like gjensen and Nambroth explain this much better. There are so many if's and's or butt's in Marek's, it's hard to pinpoint solid symptoms or methods to induce resistance. There are so so many factors considered for resistance , and possible false negatives as well. Stress can be a factor? Is missing a meal stress?

I would still like to look into trying exposure during the first 2 weeks and then removal of the chick for 2-4 months. I don't know how long to expose the chicks, but it might be a good way for backyard owners that have no access to a lab.

A variety of people approach this in a variety of ways. I did a lot of speculation along the way, but at some point I had to bring it to a practical conclusion. The conclusion is that I will emphasize health and vigor alone, until I am forced to do otherwise. All it takes is a new flock of wild birds to bring about change. I want to be realistic about what I expect from my birds. Someone was right to mention that depopulation is a temporary solution, even if it is sometimes necessary. Marek's is not something that goes away. Some breeds and strains are more vulnerable than others.
I could not picture giving up on a decade (or more) of work. If vaccination became necessary, so be it. Fortunately, that has not been the case.



Any change in a bird's routine could be considered stress, but it is unlikely to have an impact. Sustained stress like drastic changes in the weather, being transported, and being relocated etc. is real stress.

Good management means a lot. Healthy and happy birds are generally problem free. If breeding, being especially mindful of health and vigor means a lot. That comes first.

I have been to a couple places where an individual often complained of this and that, and then you see why. I would not expect anything to thrive in the settings I am referring to.

 

[Nambroth]

Good management means a lot. Healthy and happy birds are generally problem free. If breeding, being especially mindful of health and vigor means a lot. That comes first.

I have been to a couple places where an individual often complained of this and that, and then you see why. I would not expect anything to thrive in the settings I am referring to.

I would personally pay a pretty penny to get birds that are bred specifically for health, vigor and overall well-being in the long term. Even to the point of looking the other way at form, type, etc. I know some breeders would find that sacrilegious... and actually some breeders probably already do this, but I see so much emphasis put on the type/form of the bird these days (this goes for many types of domesticated critters that are often bred). Mine are pets and I love their company. I want them around for as long as reasonably possible. I love my hatchery birds very much but never again, for this reason alone. Which I know is sort of counter-intuitive for those that look for chicks with the best Marek's vaccine possible (available only at hatcheries!). It's a catch-22.

 

[tridentk9]

Apparently inhaling the MDV is worse than the injections typically used in lab testing. The full article is free. http://www.tandfonline.com/doi/abs/10.1080/03079450601156075#/doi/full/10.1080/03079450601156075

Resistant birds infected by the intra-tracheal route had an increased prevalence of tumours and shorter survival times compared with those infected by the intra-abdominal route.

Susceptible birds infected by the intra-tracheal route became paralysed 10 days after infection.

L7 birds had shorter survival times and increased prevalences of tumours than L6 birds.

L6 is the resistant line, L7 is the susceptible line. These birds were pathogen free, had never been in contact with nor vaccinated against MDV. Most of the L6 birds infected by intra-abdominal injection were still alive when the study ended 70 days post infection. Some interesting results with dosage of infection.

Chicks get their maternal antibodies mostly from yolk and some from albumin that is eaten at hatch. It was explained by one of the contributors to Avian Immunology by Schat, et al http://www.sciencedirect.com/science/book/9780123969651 I'll have to look for the write-ups on maternal antibodies.

Immunologically this shouldn't happen

Then it would be necessary to test mate and "prove" the breeders. After all of that, you would find that often those that showed some tolerance and did not become symptomatic, would not pass the trait on to it's offspring. It has been found that a bird that did become symptomatic could possibly pass the ability to resist (tolerate), to the offspring.

The bird that showed no symptoms should have a better genetic resistance and still *should* have developed antibodies, the bird that showed some symptoms *might* have more antibodies but less genetic resistance. Both should be passed on, though the antibodies will disappear within a few weeks leaving only genetic resistance.

So, I'm understanding from the big book that if a bird has tumors or enlarged nerves, most will have a positive pcr. But without symptoms or tumors, I wonder how often they have a false negative on a pcr.

Here's an article on a girl that "converted" (fought off) rabies. Some of the comments might be useful for other viral infections. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5907a1.htm

Detection of viral antibodies in serum can be indicative of previous vaccination or exposure to a lyssavirus, but does not necessarily indicate the development of disease. Contact with virus does not ultimately constitute a productive infection (e.g., the virus can be inactivated by the host innate response or by other means before replication in host cells). Similarly, a productive infection does not necessarily result in transportation of virus to the CNS. An abortive infection can occur outside the CNS, with limited replication of the virus at the exposure site and further clearance by the host immune system

This *might* be true of other viruses such as Marek's. The part about inactivation by the host's innate response can be true of MDV. And .... that leads to the question below.

Does anyone know if there is a commercially available titer test for Marek's? It would certainly help with some of the questions of exposure and resistance. IDDEXX doesn't list one. http://edis.ifas.ufl.edu/vm102

 

[gjensen]

I would personally pay a pretty penny to get birds that are bred specifically for health, vigor and overall well-being in the long term. Even to the point of looking the other way at form, type, etc. I know some breeders would find that sacrilegious... and actually some breeders probably already do this, but I see so much emphasis put on the type/form of the bird these days (this goes for many types of domesticated critters that are often bred). Mine are pets and I love their company. I want them around for as long as reasonably possible. I love my hatchery birds very much but never again, for this reason alone. Which I know is sort of counter-intuitive for those that look for chicks with the best Marek's vaccine possible (available only at hatcheries!). It's a catch-22.

I do not know what everyone does or does not. I know what you are saying though.

I am not going to look away concerning type and color. I do believe that health and vigor comes first. It has to. Everything else is for naught otherwise. Not to mention that a vigorous flock has a way about them that makes that much more enjoyable.
My birds are not "pets", but I enjoy them as if they were.

I would say that if you found a breeder of a breed that has been successful over a long period of time, you would do well. That level of commitment by someone usually means a sincere breed enthusiast that wants to do well by the breed. Well bred birds tend to have good long term health.
I can think of a few good ones off the top of my head. The catch is what you mentioned. You may have to vaccinate the young birds yourself. That is if you want them vaccinated, or need them vaccinated.