Moving Forward- Breeding for Resistance to Marek's Disease

[speckledhen]

Quote: They test for Pullorm and Typhoid, two diseases mostly eradicated now, and sometimes AI, once a year, however, unless you pay extra and test every quarter, they DO NOT test for Mycoplasmosis nor Coryza or any of the usual respiratory illnesses. NPIP was not set up originally for backyard flocks, but to protect the food supply.

 

[gjensen]

I have been reading a lot of posts about wild
birds carrying Marek's . Me-I feel that there is most likely and least likely about how Marek's gets to a flock. I think the most common way for Marek's to get into a flock is by a Marek's exposed chicken.

I feel that the wild bird route is possible but is a least likely .

The important thing is flock history. Prior to the first bird getting symptoms, did you bring home any chicks or chickens in the last 4-12 weeks?

If you have only hatched every single chick or bought day olds straight from a hatchery, and your flock gets Marek's, it's more or most likely that the virus came in on wild birds, shoes, etc.

A wild bird I believe is least likely to infect your flock. Unless your neighbor has chickens, or chickens nearby and the wild bird is a frequent visitor.

How often do flocks get tested for NPIP? Do you need that to show? Maybe they should add Marek's to the testing.

I agree that it is possible, but is more often brought in with another chicken(s).

Something about Marek's that is unique compared to some illnesses is that it is possible to not know you brought it in until you start growing out the next generation. I could be vulnerable to not knowing given I have 18 different pens scattered over a couple acres.
I do not use all of the pens all year.

 

[Nambroth]

Several years ago - someone from Europe was expressing the opposite view of many in the States...they were saying that they wished people wouldn't vaccinate for Merek's because then they take their vaccinated bird to a show, it sheds Merek's and infects the bird in the next cage - and Merek's is brought home from the show-- This may be extreme....and he may have been lamenting to prove a point. In the USA there is a tendency IMO to over medicate chickens - I see a lot of people asking for help on the forum and a large number of replys will go straight to the pharmaceuticals. I'm not sure that vaccination (except for the 18th day to the embryo) is the answer to solve the problem. I appreciate that many people will choose this - and that will give their own flock protection - from the tumors, and the worst symptoms - but I think it needs to be clearly understood that the virus can still be carried by a vaccinated chicken.

The bolded statement above may just be poor wording, but it comes across as misunderstanding of the vaccine. A vaccinated bird will not shed virus by simple virtue of being vaccinated. The vaccination will not cause a chicken to shed Marek's. If a chicken is vaccinated, but is never exposed to Marek's (MDV1) virus, it will never shed virus.

An exposed bird will shed virus regardless of being vaccinated or not.

Let me propose a scenario:
All three chickens are from different flocks, owned by different breeders, that plan to show.
Chicken A has been properly vaccinated against Marek's as a day-old chick.
Chicken B has not been vaccinated, but has a robust immune response.
Chicken C has not been vaccinated, and has an average or below average immune response.

All three chickens are exposed to the same serotype and strain of Marek's (this is important*).
Chicken A does not develop symptoms, but does shed the virus in unknown quantities. It is taken to show and spreads Marek's virus dander.
Chicken B does not develop symptoms, but does shed the virus in unknown quantities. It is taken to show and spreads Marek's virus dander.
Chicken C does develop symptoms, and either dies or is not shown because it acts sick. Either way, it does not have a chance to spread dander at the show.

All three chickens have, at this point, infected all of their flock mates. All flock mates will become carriers, regardless of showing symptoms or not.

So often I see the argument that one should not vaccinate, because at least that way you KNOW which chickens get Marek's. This is sometimes true, and a valid concern.
But, what about unvaccinated chickens, that develop natural resistance? How do you know if they have Marek's or not? You don't. Just like you don't know if a vaccinated bird (that is showing no symptoms) has it or not. You just don't know unless they demonstrate symptoms (or if you KNOW they have been exposed to the virus-- then they do have it).
What is the difference between chicken A and chicken B? Both can shed the virus with no one knowing.

Do you understand what I am getting at? In terms of showing and spreading the virus, both scenarios would have the same end result.

* - the strain of Marek's is important, because it has been shown that the more virulent a strain is, the more virus a chicken will shed in its dander.

 

[speckledhen]

Two questions, please bear with me, though I may be beating a dead horse by asking:

1) How could a pathologist tell a Marek's tumor from one of the common benign or other tumors that laying hens get? Do they say "likely" it's Marek's because of the type of tumor, the location of it, or the number of them? Or do they just see so much of this disease that they automatically jump to that conclusion?

2) If you have zero indications/factors for the disease in the flock and suddenly a necropsy unexpectedly seems to show the disease (or they think it is because of question #1) when there are other factors contributing to death, how likely is it that it is a false diagnosis? Certainly, that would be possible unless there is a tissue test that is accurate for a tumor to say, yup, that's what it is. This always bothers me because it can change your entire existence as far as the flock is concerned. Laying hens do get small tumors in and along the reproductive tract that are not caused by any virus, so why not other types as well that are not of huge concern? See excerpt below--I've seen this type of tumor in hens who died from internal laying and/ or simple reproductive cancer.

Quote from http://www.reeis.usda.gov/web/crisp...in-aging-and-aged-commercial-laying-hens.html

​

​

I know I'm driving you all crazy here, but I have to type this out, if just for myself. I realize that tumors will be in other locations like spleen and intestines with MD, but there must be other things which may cause tumors as well. I've often wondered about lead poisoning in small doses. The former owner of this property sat on the deck and shot at crows and whatever else and after over 12 years, I'm still finding handfuls of those tiny .22 shell casings and occasional shotgun shells all over the place, so I know there is buckshot all in the soil, too. He must have done every day he owned the place until he died. What happens to hens who ingest all that lead?

One person who saw photos I took said the first hen's liver looked like blackhead (a knowledgeable someone who has seen that disease). I thought it resembled Spotty Liver Disease/ Vibrionic Hepatitis. which is on the rise and hits young layers in their prime, but he'd never seen that in person. Another said it looked like Marek's or LL, but I don't see how, and maybe it's something else entirely that killed her liver, but can't test her now since that ship has sailed. The hen I had necropsied three months later (no final report, just two sets marked "preliminary findings") had a normal liver, was MG-free, but a huge reproductive infection and worms plus some other ominous stuff I have to clarify with the vet tomorrow.

I've had so many broodies with chicks wander all over this place for weeks on end, one right now has 7 week old chicks, foraging on the same ground as the hen with the abnormal liver and the second hen, and not one single chick ever died or became ill or lame or paralyzed, not one, not ever. No teenage birds have fallen ill, either. I have a group of five youngsters who are 25 weeks old and all seem vibrantly healthy-they were raised by that same broody and went everywhere here. Every group here has wandered over the same grounds for all the years I've had my own flocks (9 years) and nothing. Yes, birds can be without symptoms in a flock that is positive for the disease, but without ANY outward signs from ANY bird, ever? If it's here, why the heck is it not hitting the young? That is what is making me insane, it does not make any sense to me. How are the internal signs of MD different from other diseases enough to be 100% sure of the diagnosis? Things have to make sense to me, somehow.

My husband says he wants to get his own microscope for diagnosing chicken stuff and learn what to look for. I don't have the money to send off samples for multiple birds to Texas A&M for PCR tests (we are retired military) or drive 2 hours one way to the lab every time a bird dies, so I know where he's coming from, just not sure he can diagnose much more than worms or take guesses at other stuff.


I'm off to bed. Woke with bad headache, fighting it all day, now going to try to sleep without waking at 3 a.m. and thinking about all this. Thanks again for letting me spout off everything that's on my mind right now. You guys are swell, you really are. Thanks so much. G'nite, all.

 

[seminolewind]

Okay. From what I know, to diagnose Marek's is 3 factors: gross exam , microscopic exam and pcr. Tumors are normally sent for further examination and they can tell if it's a Marek's tumor after testing. If there are no tumors, you get a pcr, and yes, I've gotten 2 false negatives, because I strongly know I have it, yet the 2 hens died from something else and were not symptomatic of Marek's. So Nambroth and I still wonder if all cells are positive for Marek's , some cells, or if they are older and resistant, maybe a pcr shows negative because the concentration is not enough. I don't know.

If they find tumors, they test further to find out the cause.

Those pathologists know how to find out what kind of tumor and it doesn't matter where it is, they will get an answer.
If you want a pcr you can send blood to Texas A&M and it costs about 20$ for the test. Blood from a live chicken.

If you've had batches of chicks all along esp by broodies and not one 6-12 week old chick ever displayed Marek's symptoms, I strongly doubt you have it. My last 3 died at 8 months old with paralysis and wasting, but 4 years ago, I had 8 ten week olds and they got paralysis one by one and were euthanized. They were from Marek's resistant parents. If you have deaths from Marek's it will attack chicks. Or with adults, you will say to yourself "I can't figure out why some of my chickens are dying. They just stop eating and waste away ." Most of mine looked like they were eating but weren't. Some would go to the feed and just kind of stare at it. Other than that, they acted fine.

They do investigate tumors-they must chop them up and look at them microscopically and certain things tell them what kind of tumors there are. That's a necropsy-an investigation by an expert. I'd like to shoot anyone that can look at a spotty liver and say oh it looks like Marek's, LL, or any other funky illness. Because if they are not a poultry pathologist, they are guessing, and even a pathologist needs to do their investigation before they say anything. All this "I think it's......" by people has to be put into perspective. Lay people give "lay" answers. Professionals give better answers, pathologists want PROOF to go with their answers.

One person who saw photos I took said the first hen's liver looked like blackhead (a knowledgeable someone who has seen that disease). I thought it resembled Spotty Liver Disease/ Vibrionic Hepatitis. which is on the rise and hits young layers in their prime, but he'd never seen that in person. Another said it looked like Marek's or LL, but I don't see how, and maybe it's something else entirely that killed her liver, but can't test her now since that ship has sailed. The hen I had necropsied three months later (no final report, just two sets marked "preliminary findings") had a normal liver, was MG-free, but a huge reproductive infection and worms plus some other ominous stuff I have to clarify with the vet tomorrow.

A normal liver, mg free, a reproductive infection and worms does not look anything like blackhead, Marek's or LL. Those who looked at your pics were way way off with their guesses.

 

[seminolewind]

Hi all. I've read a few posts so far and would like to continue to learn from your posts.

I'll make sure to start from the beginning of the post so that I don't als already answered questions.

Welcome and ask away!

 

[gjensen]

Two questions, please bear with me, though I may be beating a dead horse by asking:

1) How could a pathologist tell a Marek's tumor from one of the common benign or other tumors that laying hens get? Do they say "likely" it's Marek's because of the type of tumor, the location of it, or the number of them? Or do they just see so much of this disease that they automatically jump to that conclusion?

2) If you have zero indications/factors for the disease in the flock and suddenly a necropsy unexpectedly seems to show the disease (or they think it is because of question #1) when there are other factors contributing to death, how likely is it that it is a false diagnosis? Certainly, that would be possible unless there is a tissue test that is accurate for a tumor to say, yup, that's what it is. This always bothers me because it can change your entire existence as far as the flock is concerned. Laying hens do get small tumors in and along the reproductive tract that are not caused by any virus, so why not other types as well that are not of huge concern? See excerpt below--I've seen this type of tumor in hens who died from internal laying and/ or simple reproductive cancer.

I know I'm driving you all crazy here, but I have to type this out, if just for myself. I realize that tumors will be in other locations like spleen and intestines with MD, but there must be other things which may cause tumors as well. I've often wondered about lead poisoning in small doses. The former owner of this property sat on the deck and shot at crows and whatever else and after over 12 years, I'm still finding handfuls of those tiny .22 shell casings and occasional shotgun shells all over the place, so I know there is buckshot all in the soil, too. He must have done every day he owned the place until he died. What happens to hens who ingest all that lead?

One person who saw photos I took said the first hen's liver looked like blackhead (a knowledgeable someone who has seen that disease). I thought it resembled Spotty Liver Disease/ Vibrionic Hepatitis. which is on the rise and hits young layers in their prime, but he'd never seen that in person. Another said it looked like Marek's or LL, but I don't see how, and maybe it's something else entirely that killed her liver, but can't test her now since that ship has sailed. The hen I had necropsied three months later (no final report, just two sets marked "preliminary findings") had a normal liver, was MG-free, but a huge reproductive infection and worms plus some other ominous stuff I have to clarify with the vet tomorrow.

I've had so many broodies with chicks wander all over this place for weeks on end, one right now has 7 week old chicks, foraging on the same ground as the hen with the abnormal liver and the second hen, and not one single chick ever died or became ill or lame or paralyzed, not one, not ever. No teenage birds have fallen ill, either. I have a group of five youngsters who are 25 weeks old and all seem vibrantly healthy-they were raised by that same broody and went everywhere here. Every group here has wandered over the same grounds for all the years I've had my own flocks (9 years) and nothing. Yes, birds can be without symptoms in a flock that is positive for the disease, but without ANY outward signs from ANY bird, ever? If it's here, why the heck is it not hitting the young? That is what is making me insane, it does not make any sense to me. How are the internal signs of MD different from other diseases enough to be 100% sure of the diagnosis? Things have to make sense to me, somehow.

My husband says he wants to get his own microscope for diagnosing chicken stuff and learn what to look for. I don't have the money to send off samples for multiple birds to Texas A&M for PCR tests (we are retired military) or drive 2 hours one way to the lab every time a bird dies, so I know where he's coming from, just not sure he can diagnose much more than worms or take guesses at other stuff.


I'm off to bed. Woke with bad headache, fighting it all day, now going to try to sleep without waking at 3 a.m. and thinking about all this. Thanks again for letting me spout off everything that's on my mind right now. You guys are swell, you really are. Thanks so much. G'nite, all.

After reading this, I wonder if you have Marek's myself. Most birds become symptomatic around 12wks. I realize that there are exceptions and there is a range, but most often that is the case. Generally if the infection is present, you start seeing it in the young birds. Breeders rarely have trouble with the adults on any scale, but have problems with their growers. That is one of the problems with breeding away from it. The offspring have to be tested, so to speak. Breeding non symptomatic offspring from non symptomatic parents that produced the best percentages. Otherwise the progress is very slow and you lose a lot of growers. Note . . . lose a lot of YOUNG birds.

I also noticed that you have not mentioned any cockerels becoming symptomatic.

These things do not rule it out, just makes it much less likely.

What breed was these birds, and do you still have the pictures? I would like to see the pictures.

 

[tridentk9]

There are studies about if a vaccinated chick grows up and gets exposed, they may shed less virus than an unvaccinated bird, but it's research.

http://m.vir.sgmjournals.org/content/88/8/2121.long

In summary, this study has shown that: (i) all three serotypes of MDV are detectable in feather dander, even when all three are co-existing in the same population; (ii) there was no significant difference in viral shedding rates among three isolates of MDV1 of broadly similar virulence; (iii) vaccination with HVT alone or in combination with MDV2 had only limited effects on shedding of MDV1 by infected chickens; (iv) shedding of the vaccinal viruses MDV2 and HVT increases significantly with co-infection with virulent MDV1; (v) a commercial broiler chicken challenged with 500 p.f.u. MDV1 on day 5 of age sheds approximately 1,000,000,000 copies of the MDV1 genome per day from day 28 onwards, irrespective of vaccination status; and (vi) qPCR assays can play an important role in the monitoring of MD status in poultry flock by assaying MDV load in feather dander.

 

[ChicKat]

Do you understand what I am getting at? In terms of showing and spreading the virus, both scenarios would have the same end result.

* - the strain of Marek's is important, because it has been shown that the more virulent a strain is, the more virus a chicken will shed in its dander.

Yes, I do see what you are saying and I think that the examples are very good....One thing that I would consider, is that taking a chicken to a poultry show - would expose that chicken to a number of things, not only from the show chickens, but from the people walking in the arena. Add to that the stress of travel, being removed from their home, spending a day or two and over nights in the show room - it has to be pretty stressful on the individual chicken. -- And stress can open the door to many diseases. So for one thing, show chickens are very hearty to withstand it, and a second point that a chicken in a show - will probably be exposed to something new IMO.

http://m.vir.sgmjournals.org/content/88/8/2121.long

(v) a commercial broiler chicken challenged with 500 p.f.u. MDV1 on day 5 of age sheds approximately 1,000,000,000 copies of the MDV1 genome per day from day 28 onwards, irrespective of vaccination status;

So - a billion copies of the virus...

 

[speckledhen]

After reading this, I wonder if you have Marek's myself. Most birds become symptomatic around 12wks. I realize that there are exceptions and there is a range, but most often that is the case. Generally if the infection is present, you start seeing it in the young birds. Breeders rarely have trouble with the adults on any scale, but have problems with their growers. That is one of the problems with breeding away from it. The offspring have to be tested, so to speak. Breeding non symptomatic offspring from non symptomatic parents that produced the best percentages. Otherwise the progress is very slow and you lose a lot of growers. Note . . . lose a lot of YOUNG birds.

I also noticed that you have not mentioned any cockerels becoming symptomatic.

These things do not rule it out, just makes it much less likely.

What breed was these birds, and do you still have the pictures? I would like to see the pictures.

The first hen who died was a Delaware X, her mother was not sure, thought it was my Amerau/EE/Whatever she is (Tiny), but after seeing s some of the later black pullets, it was more likely my 4 year old Blue Rock hen, Neela. Her eggs and Tiny's are similar when Neela lays a smaller egg. The second hen was also a Delaware X, but her mother was one of the Stukel line Barred Rock hens, who are approaching 4 years of age. So, these hens were both sired by Isaac and hatched the same time. They were both a year old in June. The first died in June almost exact at her first hatch day, the other three months later. They were always together on range, which made me think they may have gotten into something toxic.

No cockerels have been symptomatic, no. None, nada. My thread on Atlas linked in my sig line, he is 25 weeks old, and he and his sisters were raised free ranging all over this property. There's one cockerel as an example who still lives here and grew up here. My Stukel Rock hen, Dottie, raised them. And now, she has three chicks, two are cockerels, who are 7 weeks old now, doing the same thing, going all over the place, ranging the same areas as those two hens. Last year, I had a bunch of youngsters out of my Blue and Splash Rock hens as well as the first hen who died. Most of them went to live in Kentucky, two cockerels and two pullets with Cetawin (she rehomed one male) and two cockerels and two pullets to her neighbor in the area. None show symptoms of anything. I raised up two here that I later rehomed myself who were robust and healthy. So, not one male ever showed signs of this disease, either.

This is why I would have to challenge any diagnosis of MD at this point in time. If it is, then it is, but it does not make sense to me. I have two cockerels who are spoken for, but I cannot let them leave if there is a chance they could be carriers, those two with Dottie. This is one reason it's critical for me to know. It's not a casual thing for me like it seems to be with some folks here on BYC.

It also bothers me how one hen could have a spotty liver and the other one have a healthy looking liver if they both had this disease. Seems if it was the visceral type, they'd both have a traumatized liver, but I could be wrong about that.

I'll check for the photos in my folders, though I hesitate to post anything here of that nature that I'm not sure of yet. I want to educate and I like to know the answers before I show that type stuff; call me rude, but I do not want someone who knows nothing, and I'm not referring to the people on this thread, mind you, throwing out guesses like they sometimes do on breed and sex. I have enough stress.



In light of the showing thread, where NPIP testers are taking birds from MD-positive flocks to show, I want to know this: Hypothetically, if someone applies to be NPIP certified and the state knows that they have Mareks in their flock already, will they still certify them???? I thought of that last night.