Moving Forward- Breeding for Resistance to Marek's Disease

[gjensen]

George, you'll love this one. I read your response and had a V8 moment. I had read a possible reason just needed to find the article.
http://m.jeb.biologists.org/content/217/5/682.full

If you exchange disease resistance for the mention of height, this article on additive inheritance might explain a genetic reason: http://bowlingsite.mcf.com/Genetics/GenSize.html
Given the life of some birds- if they survive that, they're probably a very hardy line. It's one thing to survive when kept in the best of conditions- such an individual does have a lot going for it. But to survive and even fight off disease when diet, environment, disease exposure level, climate, stress, etc of the individual (and it's ancestors) is difficult speaks even more.

Giving chickens the best of care is commendable and is best for the individual bird, but it can sometimes be detrimental to the flock, breed or species. Sometimes a hard life is good.

Resistant does not mean an individual will never get sick just that it is less likely to get sick than the average. If it does get sick the odds are that it will be a lighter case. Susceptible is more likely to get sick than average and will be sicker.

Thank you for this. I will check this out this evening.

I opened up Genetics of the Fowl ( F.B. Hutt) this morning. There is a chapter on this subject. It is an older book, and some information may be outdated, but it is easy to read. The fundamentals are there. It is a good read.

 

[seminolewind]

gjensen:
Mixed flocks used to be common on farms. They were more or less useful, depending on what you compared them to and how you compared them. It was not uncommon to bring in a purebred male from a high performing strain periodically. This would be to keep the production level up, or make improvements.

This was before Marek's became a problem for backyard owners. As commercial production companies learned how to reduce their Marek's problems, there became an immense increase of backyard chicken ownership not practicing the methods that improved commercial flocks.

Although you can breed for resistance, at this point you can't breed to prevent exposure and shedding of the virus, just the deadly symptoms. The vaccine does not prevent marek's , it prevents the exposure from the symptoms (tumors and nerves, etc). How can one breed chickens that protect against the virus from being carried and exposing others?

I will add statements from the Saif book later, but I know it says that there is a period of weeks that the virus is shed in larger amounts. The strains are not really different, just virulent, very virulent, very very virulent and vvv virulent. The differences in what is attacked in their body is caused by the area of least resistance. Most commonly that would be the sciatic nerves. But will spread based on which areas are easiest to invade.

I'm not sure about the ocular form or the outer skin form-whether there's a different form for that. But my first rooster had the leg paralysis first, the wasting and ocular gray eye. I assumed from the same virus.

 

[tridentk9]

From what I've read, genetic resistance to MDV in chickens is similar to genetic resistance to AIDS in humans. Wired has a good (though older) article explaining genetic resistance with AIDS.

http://archive.wired.com/medtech/health/news/2005/01/66198?currentPage=all

All those with the highest level of HIV immunity share a pair of mutated genes -- one in each chromosome -- that prevent their immune cells from developing a "receptor" that lets the AIDS virus break in. If the so-called CCR5 receptor -- which scientists say is akin to a lock -- isn't there, the virus can't break into the cell and take it over.

To be protected, people must inherit the genes from both parents; those who inherit a mutated gene from just one parent will end up with greater resistance against HIV than other people, but they won't be immune. An estimated 10 percent to 15 percent of those descended from Northern Europeans have the lesser protection.

Using formulas that estimate how long genetic mutations have been around, researchers have discovered that the mutation dates to the Middle Ages. (Similar research in mitochondrial DNA -- passed along by women -- has suggested that Europeans are all descended from seven Ice Age matriarchs.)

It has been realized that people with two copies of the CCR5 mutation are more susceptible to fatal West Nile Virus disease.

Sigh, I've been thinking about this from more of a genetic based (breeding) point of view but looking at resistance from an environmentally acquired POV is also valid. While testing in a lab can separate the two, when living in the "real world" the two are inextricably intertwined. It is both a plus and a minus.

MDV affecting the eye *may* be related to the Harderian gland located near and connected with the structures involved with the eye. It's part of the immune system, disease may cause some reaction within the gland opening the door to MDV related changes.

IMO Genetic information lately has been changing at an exponential rate even faster than computer programs.

I agree, this has been a wonderful discussion. Multiple people with different focuses and experiences exchanging information.

 

[tridentk9]

Hmmmm. In vitro effects of plant and mushroom extracts on immunological function of chicken lymphocytes and macrophages http://www.tandfonline.com/doi/full/10.1080/00071661003745844 Only the abstract is free at the moment. First stage of testing.

Abstract
1. The present study was conducted to examine the effects of organic extracts from milk thistle (Silybum marianum), turmeric (Curcuma longa), reishi mushroom (Ganoderma lucidum), and shiitake mushroom (Lentinus edodes) on innate immunity and tumor cell viability.

2. Innate immunity was measured by lymphocyte proliferation and nitric oxide production by macrophages, and the inhibitory effect on tumor cell growth was assessed using a non-radioactive assay. For measuring the cytokine levels in the HD11 macrophages which were treated with extracts of turmeric or shiitake mushroom, the levels of mRNAs for interferon-α (IFN- α), interleukin-1β (IL-1β), IL-6, IL-12, IL-15, IL-18, and tumor necrosis factor superfamily 15 (TNFSF15) were quantified by real time RT-PCR.

3. In vitro culture of chicken spleen lymphocytes with extracts of milk thistle, turmeric, and shiitake and reishi mushrooms induced significantly higher cell proliferation compared with the untreated control cells. Stimulation of macrophages with extracts of milk thistle and shiitake and reishi mushrooms, but not turmeric, resulted in robust nitric oxide production to levels that were similar with those induced by recombinant chicken interferon-γ. All extracts uniformly inhibited the growth of chicken tumor cells in vitro at the concentration of 6·3 through 100 µg/ml. Finally, the levels of mRNAs encoding IL-1β, IL-6, IL-12, IL-18, and TNFSF15 were enhanced in macrophages that were treated with extracts of turmeric or shiitake mushroom compared with the untreated control.

4. These results document the immunologically-based enhancement of innate immunity in chickens by extracts of plants and mushrooms with known medicinal properties in vitro. In vivo studies are being planned to delineate the cellular and molecular mechanisms responsible for their mechanism of action.

 

[speckledhen]

I've re-read sassybird's first post several times. Sounds so much like me, being so careful to practice reasonable biosecurity, yet she still has had the MD diagnosis and has had to put down young birds. I've also seen reports that, amidst the long words and all the strange stuff, that use phrases like "likely MD" or "consistent with MD". How common would a false positive report be, do you think? Makes me wonder if they see so much of this that if they see a tumor, they automatically just diagnose it as MD because of their experience and not because tissues showed MD through the actual testing. We know of false positives with human diagnostic testing, why not with chickens? We can't live our lives on "looks like" or "might be" or "could be". I know I can't.

 

[gjensen]

gjensen:
Mixed flocks used to be common on farms. They were more or less useful, depending on what you compared them to and how you compared them. It was not uncommon to bring in a purebred male from a high performing strain periodically. This would be to keep the production level up, or make improvements.

This was before Marek's became a problem for backyard owners. As commercial production companies learned how to reduce their Marek's problems, there became an immense increase of backyard chicken ownership not practicing the methods that improved commercial flocks.

Although you can breed for resistance, at this point you can't breed to prevent exposure and shedding of the virus, just the deadly symptoms. The vaccine does not prevent marek's , it prevents the exposure from the symptoms (tumors and nerves, etc). How can one breed chickens that protect against the virus from being carried and exposing others?

I will add statements from the Saif book later, but I know it says that there is a period of weeks that the virus is shed in larger amounts. The strains are not really different, just virulent, very virulent, very very virulent and vvv virulent. The differences in what is attacked in their body is caused by the area of least resistance. Most commonly that would be the sciatic nerves. But will spread based on which areas are easiest to invade.

I'm not sure about the ocular form or the outer skin form-whether there's a different form for that. But my first rooster had the leg paralysis first, the wasting and ocular gray eye. I assumed from the same virus.

I want to reiterate that my position is that you can breed for resistance. I have just wanted to communicate my position that it is easier said than done. Just the fact that some strains are more susceptible than others is proof that it is possible.
Early in the commercial industry some breeders tolerated and culled. They found it better to withstand minor losses in their own flocks rather than sell highly susceptible stock.
In other words it was considered better by some to lose 20-25% of their young birds vs. selling birds where 75% could be lost by 16wks. Those numbers are only an illustration. The concept caught my attention because that is a lot different than how we would operate today.

"Backyard flocks" or small farms used to be more isolated. Also losing a percentage of their offspring was considered acceptable. Where if we lose a single chick, we are trying to figure out why, they considered it par for the course. They would have considered a very good year losing 5-10%, where I have lost a single chick out of a couple hundred in the last two years. That was unheard of in "the old days".

Preventing the spread is only done by isolation, and limiting exposure. Some older literature noted the difference in incidence levels of growers by distances from the main flock. Once a young bird is @ the 20wk range it is not likely to succumb to the disease whereby it could be introduced to the main flock or adjacent facilities.

I think it is helpful to consider that there is different strains. There is enough difference to make one more virulent than another. Possibly this is not technically correct, but I do not know why it wouldn't be.

There is a difference among breeds and strains of breeds that dictate what the incidence level of tumors in different places would be. That is correct according to how I understand it. I always took notice to mention of breeds (or strains) that were reported to be resistant or highly susceptible.

 

[gjensen]

I've re-read sassybird's first post several times. Sounds so much like me, being so careful to practice reasonable biosecurity, yet she still has had the MD diagnosis and has had to put down young birds. I've also seen reports that, amidst the long words and all the strange stuff, that use phrases like "likely MD" or "consistent with MD". How common would a false positive report be, do you think? Makes me wonder if they see so much of this that if they see a tumor, they automatically just diagnose it as MD because of their experience and not because tissues showed MD through the actual testing. We know of false positives with human diagnostic testing, why not with chickens? We can't live our lives on "looks like" or "might be" or "could be". I know I can't.

"Likely" and "consistent with" is through out my personal medical records. For me it means that they aren't certain because there is not specific enough testing available to prove it one way or the other. My condition is poorly understood, and rare enough for there to be a lack of research.
Whenever "likely" and "consistent with" is used, it could certainly could be something else. For the subject that we are discussing, you can pretty safely assume it is what is implied. The likelihood of it being something else is pretty slim.

I do not have a choice but to live with "looks like" or "might be". LOL.

I always raised the young separate from the adults, and it might have helped me avoid problems. The distance would be 300' - 400'. A problem is that I have come to enjoy watching a hen raise her own, so that will likely change.

 

[speckledhen]

"Likely" and "consistent with" is through out my personal medical records. For me it means that they aren't certain because there is not specific enough testing available to prove it one way or the other. My condition is poorly understood, and rare enough for there to be a lack of research.
Whenever "likely" and "consistent with" is used, it could certainly could be something else. For the subject that we are discussing, you can pretty safely assume it is what is implied. The likelihood of it being something else is pretty slim.

I do not have a choice but to live with "looks like" or "might be". LOL.

I always raised the young separate from the adults, and it might have helped me avoid problems. The distance would be 300' - 400'. A problem is that I have come to enjoy watching a hen raise her own, so that will likely change.

Thank you for your answer. I still haven't had anyone really address my question so I wonder if I'm not making myself clear. I'm sorry if I'm not. When they say it's "likely" Marek's, that does not sound as if they've put the tissue of a tumor or whatever on a slide, added some agent that turns some color (only example I could think of) and saw something that says, "YES, this color indicates the Marek's virus in this tissue!" Do they do that or is it only visual? Considering that there are several diseases that can cause weird livers and cancers other than MD. Gatherings of odd cell growths are not always cancerous, either.

Do you see what I'm saying? Though the virus may be common, it seems that folks jump to the MD conclusion so quickly when other things can mimic MD. A bird limps and someone screams, "Mareks!" when all it did was sprain its leg.

I did read all of Jennifer's FAQ so part of what I'm asking sort of was prompted by that long read. I know my birds are MG/MS free, which everyone says is near to impossible, but those tests seem more definitive than the ones for MD, they are not visual observations. All of this reading is making me feel hopeless and then, when I see supposedly respected breeders selling and showing birds from their MD-positive flocks, that makes me insanely angry, to think they are helping to cause all this heartache we are seeing on this thread and others. I'm going to have to find a way to feel about this, a philosophy about it, so I can stop obsessing over it. I don't feel as if I'm helping here.

 

[seminolewind]

I've re-read sassybird's first post several times. Sounds so much like me, being so careful to practice reasonable biosecurity, yet she still has had the MD diagnosis and has had to put down young birds. I've also seen reports that, amidst the long words and all the strange stuff, that use phrases like "likely MD" or "consistent with MD". How common would a false positive report be, do you think? Makes me wonder if they see so much of this that if they see a tumor, they automatically just diagnose it as MD because of their experience and not because tissues showed MD through the actual testing. We know of false positives with human diagnostic testing, why not with chickens? We can't live our lives on "looks like" or "might be" or "could be". I know I can't.

LOL. That's all you're going to get about Marek's , likely, commonly, could be, consistent with, chances , does not look like............... the more we know about Marek's the more we don't know. I've read there's 3 parts to the testing. 1- examination for tumors. 2. examination of tissue microscopically. 3. a PCR. Not necessarily in that order . A lab will say positive or negative for tumors, enlarged nerves or a PCR. Based on that information, a vet at a disease lab would base his answer accordingly.

I've had 2 negative now. But they were not symptomatic of Marek's.

George, quote: Once a young bird is @ the 20wk range it is not likely to succumb to the disease whereby it could be introduced to the main flock or adjacent facilities.

Good thing you said "not likely", because I've had some up to 8 months old, and my first was 18 months old and had every classic symptom.

Within the last 2 days my BR Fern has succumbed to paralysis. Today she can't even hold herself upright with her wings. She's 5 years old. I'll be sending her out for a necropsy and it will be the first one I"m sending that's actually symptomatic..

A few years back, I had 3 chicks from different sources. At 4 months old, they were put out with the flock. A month later, one started to waste and died. One other wasted and died at 8 months old. I didn't know I had Marek's at the time. The rooster lasted almost 1.5 yr old, when I noticed his pupils had an odd shape to them. He wasted away and died. One hatched by me, one egg hatched that was laid in my car, and one chick from a friend.

There are no rules or solid symptoms.

 

[speckledhen]

I want to say something the censor will catch.

I'm so sorry about your Fern.