Moving Forward- Breeding for Resistance to Marek's Disease

[Nambroth]

I am not being snarky-- I am genuinely curious here: Has anyone ("anyone" being, anyone in the world-- not just here on the forum) ever established that they have truly, successfully bred any given domesticated animal for true resistance to a virus via natural immune system only (no vaccination)? How is this determined? Can it even be done with the numbers of chickens we keep?

The studies I've read about were selectively breeding for resistance have mostly been done with produce, where hundreds and hundreds of samples are selectively bred over the period of many years. Even resistant cultivars, when bred in the traditional way, did not show nearly the resistance as those that have been genetically modified by modern science (and I am defining this as the introduction of gene sequences into the DNA that could never have gotten there without laboratory help). Is breeding for resistance a pipe dream for the average backyard chicken keeper? I am not suggesting that it's not a good idea to only breed what appears to be your healthiest, most vigorous birds, but is it even possible to say that one has a Marek's resistant flock? Anecdotal "well none have died from it in a few years" is... not good science, is it? Of course, we can all only rely on our experiences. So how does one separate the "everything seems to be okay" from "everything IS okay" without vigorous testing and extremely good record-keeping of a large number of birds?

Even if we had a cheap test at home, there is no technology available to anyone-- even the best labs-- that is completely conclusive. As some of us are finding out, even the PCR testing can be iffy unless the bird has tumors and samples from those are tested.
How many here have even had full necropsy and testing of each bird that passes? I have, but I've lost very few. I imagine if I was keeping a large number of birds-- enough to be able to breed properly, that if I lost a few every year the expense would get pretty high indeed. I do not live in a state that offers free necropsy. I have to pay for additional testing on top of the necropsy, as well, if I want PCRs run. I know a few of you get birds tested, and that's great, but for the average keeper...?

I am not arguing against breeding only your healthiest stock. I am only wondering how realistic we are being in our abilities to breed resistance in our backyard flocks. The genetics relating to virus tolerance is still not well understood even by experts (which is why we still have so many problematic human viruses!). What hope do we have as laypersons? This is not meant to question anyone's motives or abilities to breed their birds well! I know it's hard to read emotion into text. I'm not trying to be snotty about this, I'm just concerned. It seems that we keep circling around the issue. No matter what, though, the conversation is very educational and important.

 

[speckledhen]

You ask some very valid questions, Jennifer. I don't take any of what you said as snarky at all. Backyard flock owners are limited in many ways. I don't know the answers. All I can do is breed for the strongest immune systems and the healthiest birds I can and practice reasonable biosecurity and hope that is enough for them to "block" bacteria and viruses that are lurking in our environment. Beyond that, I dunno.

My "long-distance" vet is back in town (Cetawin's vet in Kentucky) and he is going to look at the report she got back on her bantam hen as well as the preliminary report I received. He knows the history of my flock and what I have and have not seen. He was skeptical that I would have Marek's here from what he knows of my birds and the flock history, but I will be curious to get his take on the prelim if he has time to look at it tomorrow-he is stopping by Ladyhawk's to check her injured cockerel, one of many who journeyed from my place to hers in the last couple of years. He possibly has a compression fracture, though we both hope it's only a bad sprain. Praying that sweet boy will be okay-he jumped from up high down to a hard surface. This has been a stressful year for our flocks as well as in both our families. She doesn't need a bad diagnosis on one of her favorite birds.

 

[Michael Apple]

So long as industry decides the standard to which people conform, research will remain low priority. Industry regards the chicken as conveniently replaceable and short lived due to low pricing. When chicken breeds are recognized as a valuable species rather than just a food source, or that food source increases in value, then perhaps more well funded science will be dedicated to research.

 

[seminolewind]

Immunity is a big word. Does it mean Immunity will take the place of the vaccine (affecting tumors only)
Will it mean the virus does not enter the body at all? OR does it mean have an exposure does not cause tumors, manufacture virus and suppress the immune system?

What exactly is possible?

I wonder if it's possible to develop a vaccine that prevents tumors AND distorts the virus being manufactured and spread? Kind of like having a vaccine that has the ability to change the virus itself into manufacturing dander that is similar to Turkey Marek's that does no harm?

The answer may not be in prevention of exposure causing the cells to spew more virus. Maybe it's in our cells or antibodies having the ability to slightly change what the virus puts out. Which would mean producing something similar to Turkey Marek's.

From what I've read, and I"m not a scientist, there is skin and mucous as a first line of defense. Then comes B-cells which are not specific but fight the virus along with __cytes that carry a chemical to kill the invaders, and macrophages who eat the invaders and the mess, and finally T-cells that specifically target what is invading. (there's more to this but that will be tonight's reading)

So which area or stage would be best to plan this immunity?-for lack of a better word.

 

[Nambroth]

The answer may not be in prevention of exposure causing the cells to spew more virus. Maybe it's in our cells or antibodies having the ability to slightly change what the virus puts out. Which would mean producing something similar to Turkey Marek's.

That would be ideal, would it not? It would essentially kill the virus off, if enough people vaccinated. We are probably a long way out from this though, as the much more highly funded and motivated scientific teams working with human herpesvirus (herpes simplex 1 and 2) have still not found a way to stop the manufacture and shedding of virus within a host (thank heavens that it is not shed in our dander!!). Maybe someday!

 

[tridentk9]

So long as industry decides the standard to which people conform, research will remain low priority. Industry regards the chicken as conveniently replaceable and short lived due to low pricing. When chicken breeds are recognized as a valuable species rather than just a food source, or that food source increases in value, then perhaps more well funded science will be dedicated to research.

It's not up to just Industry.

My (dog) breed recently "sponsored" the search for the genes responsible for a lethal condition in very few (2!) breeds. The researchers and testing was paid for by raffles, contests, etc. Admittedly finding responsible genes is getting easier and easier with the leaps forward in genome mapping, plus they were given blood from affected individuals, their siblings, carrier parents, etc. The DNA test came out this month.

Research doesn't have to be paid for by Industry.

 

[chooks4life]

It's not up to just Industry.

My (dog) breed recently "sponsored" the search for the genes responsible for a lethal condition in very few (2!) breeds. The researchers and testing was paid for by raffles, contests, etc. Admittedly finding responsible genes is getting easier and easier with the leaps forward in genome mapping, plus they were given blood from affected individuals, their siblings, carrier parents, etc. The DNA test came out this month.

Research doesn't have to be paid for by Industry.

Very good point, many advances in just about every field only came about by some layperson's diligence and work. After the fact it's generally attributed to the field as a whole, more often than not, but much of humanities' advance is by the labor of the often nonprofessional individual. Once that initial work is done quite often the professionals investigate more deeply and build upon it.

 

[Michael Apple]

It's not up to just Industry.

My (dog) breed recently "sponsored" the search for the genes responsible for a lethal condition in very few (2!) breeds. The researchers and testing was paid for by raffles, contests, etc. Admittedly finding responsible genes is getting easier and easier with the leaps forward in genome mapping, plus they were given blood from affected individuals, their siblings, carrier parents, etc. The DNA test came out this month.

Research doesn't have to be paid for by Industry.

That isn't what I said. Industry, by and large, determines the production standard for supply and demand. So long as production meets supply and demand, they care not about longevity since it is merely a meat/egg source. That is what I stated.

 

[seminolewind]

Quote:
I think there's a lot of "distortion" added to that mix. Seems the main source for finding Marek's research is the web and when you search for something, the material that comes up is 10-40 years old, even in new articles , the information cited is old old old. It's unfortunate that we are so limited in finding current information.

Also, the only people who want to read about the research are other researchers. I don't think Frank Perdue studies Marek's research, he just wants the end product-a vaccine or a pill. BYC is a relatively new thing where we have thousands of lay people who have an interest in new research. It's unfortunate that we haven't found a reliable source where all this information is kept regularly.

But like Michael said, it's the demand that determines the supply, and that demand does not require any concern on longevity.

 

[speckledhen]

I mentioned that my long distance vet was going to consult with me about Hope's necropsy as well as look at my preliminary report. Turns out the two baseball sized side-by-side tumors in one membrane were in the left lobe of her liver and they were actually reproductive tumors! You can see them and read what he said here: https://www.backyardchickens.com/t/...ip-hope-graphic-photos-added/20#post_14280855

I still do not have a final report. Dr. Mason says he hopes I'll eventually get one, but I may not, since this state does the necropsies free and they are probably behind the eight ball. He was not pleased with the report and the way they hinted at something then left me hanging. He's had issues in Ky of unethical actions by pathologists being behind in the reports so, suddenly a preliminary becomes the final when it isn't. He also, knowing what has happened and what hasn't on my property and having seen birds that Ladyhawk has that she got from me, etc, says he has a better chance of winning the lottery than I do of having Marek's in my flock, that disease doesn't happen in a vacuum, not in one single bird that not show up in almost 50 others. Dr. Mason told me that if I end up with a final that says Marek's, that I should question it, ask what tissues they tested and what exact tests were done to determine that, that he would find the diagnosis suspect.

Dr. Mason also reviewed pics of the other hen's odd liver that LH still has on her phone (she never deletes any of my messages, must be hundreds, lol) and he said it looked exactly like Spotty Liver Disease, that it is making a comeback now. Interesting, that's exactly what I originally felt it was myself.