Moving Forward- Breeding for Resistance to Marek's Disease

[tridentk9]

I agree that it "shouldn't" happen, but it does. That is part of the reason I said that it is not that simple, and used this as an example. The inheritance of disease resistance is not as cut and dry as color genetics. I found a few examples skimming through poultry genetics books that are meant for the commercial industry. Both modern and outdated. If it was that simple, the commercial poultry industry would have their problems solved. There is plenty of economic incentive to do so. They also have the money and scale to do it. It isn't as if they have not done any work on it.
I am no expert on this subject and will not pretend to be. It is an interesting topic.

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

One of the benefits of mongrels is that they've been traveled all over, just about nobody practices biosecurity or prophylaxis with them, and they've been exposed to multiple strains of everything, then mixed, and remixed, and plenty of them have also been left neglected to try to survive without additional feeding or care, so only the fittest survived to breed.

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.

 

[speckledhen]

Our thread participants might want to comment here: https://www.backyardchickens.com/t/...-poultry-and-safety-precautions#post_14168739

I put in my two cents already and I'll probably be blasted for it by some, but hey, I'm used to it. It sucks when someone is hit by this disease and has to change their plans, but to forge ahead despite the risk to others is not right. It's selfish, plain and simple.

 

[tridentk9]

So, can a chicken have maternal antibodies against viruses? Herpes virus?
How hard is it to extract enough virus or antibody from a week old chick to be able to detect it?
How can we utilize the chick's antibody coverage for a few weeks? 

I apologize for not commenting on this question. I have to ask a few of my own. Well not to you but for you to look up in your book and/or ask an avian specialist.

Is there an antibody titer test for Marek's?
Is the virus shed when it's dormant.
Is using plasma (instead of vax) a possibility in chickens? What route? Is oral acceptable?
Will there be a problem using plasma with "original sin"

If there is a titer test, test the mother and broodmother of your upcoming hatch for antibody levels and an MDV test also. Retest titer in 4weeks to see if antibody level goes up, down, stays the same, and is it at a protective level.

If plasma is OK with chicks AND if mother's MDV -, titer is staying the same and at a protective level AND " original sin" is discussed, pull blood, spin down and give plasma to chicks.
Titer of broodmother should tell you a bit more about if she has an active infection, if it's dormant or clear.

 

[chooks4life]

I think there is some validity in what you are saying, but many points you raised (I can speak for myself) happens within a breeder's flock. What "nature" does for a land race "breed", I do for my flock. Instead of nature being the pressure, I am. If I apply pressure to a point where I only retain the fittest examples, then over time I have a flock more tolerant of my environment. But in addition to health and vigor, I have the opportunity to select good typed animals that are productive.

I think I see the cause of the confusion here... I'm not talking about landraces, but I think that's the impression you've gotten when I refer to mongrels. (?).

These mongrels I'm talking about are far more 'interfered with' or shaped by artificial/human pressures than a landrace is. They're usually also selected for productivity, but asides from that there's very little selection done, and often a whole lot of neglect. But not always.

Some owners of course don't select for or against anything. Not all mongrels are worthwhile, for sure.

Nevertheless they remain overall pretty productive because in the case of most mongrel flocks, they're not too far removed from productive types, and contrary to what some seem to believe, all those years of genetic selection for productivity does not just come out in the wash.

In some modern breeds, according to the poultry industry publications and sites I've seen, over half the spectrum of ancestral genes of the species have been lost through intensive selection for productivity. Letting most modern productive breeds 'mongrelize' can't cause reversion to a wild type that has been eradicated from their genetic inheritance.

I hear many theories of such from purebred breeders, saying things like "they will rapidly descend to a mediocre average", (referencing the wild or ancestral type returning in mongrel flocks) but I don't see it, and I don't hear mongrel breeders complaining of it, and certainly it's not happened in my flock, nor among any of the flocks that contained ancestors of my flock. From what I've seen, natural selection for wild type color returns fairly quickly in mongrel flocks, as well as feed efficiency, hardiness, and instinct levels, but that's about it as far as the 'inevitable return to mediocrity' goes... And even then, the 'wild-type coloring' shows because it's a deliberately retained phenotype, not really associated with true 'wild type' genotype. They remain fair to good layers and decently meaty birds, overall.

As far as I understand, given enough generations as a landrace, they would indeed manage, limited genepool or not, epigenetically etc, to return to the form that most suits them. But most mongrels are not being allowed to make a landrace of themselves, though they do have access to some pressures and aspects of that lifestyle as compared to the average purebred.

Another point that I would add is that just because a flock of "wild mongrels" are surviving, does not make them necessarily more resistant. I am going to use the Key West chickens as an example. Obviously they are surviving. They have adapted and are continuing to adapt to their environment. They also are not withstanding heavy exposure. They are being exposed, but the level of that exposure is relevant. Those same bird's offspring in close confinement would likely be just as susceptible as a "pure breed" that has been carefully selected on the same Island.

Again, this is referring to landraces, whereas I'm referring to mongrels people keep but neglect. They are not 'wild mongrels'; they're domestic animals of mixed ancestry, kept for agricultural purposes usually, but sometimes just as ornaments.

Obviously I'm not speaking for all mongrel-keepers but so far, every single mongrel owner I've gotten chooks from has repeatedly exposed them to numerous new birds from numerous other places, even very distant places. They have been heavily cross infected/exposed etc.

At no point would I consider an isolated landrace population on an island to be resistant to the same strains mainland animals are exposed to. They can be resistant to strains of them, but generally it's rather outdated resistance; with the rapid adaption of strains of disease constantly occurring, they would be susceptible if exposed.

Concerning the trade of mongrels. Is there a trade in mongrels?

Of course. Always has been, always will be.

What I have seen is mixed breeds being traded within a given area where the pressures are more or less uniform.

That's generally true especially when referring to custom mixes, i.e boutique crossbreds developed for a given purpose and usually sold within the limits of a certain geographical radius around each hatchery with a predetermined cull-by date practically emblazoned on their genetics, timed to deteriorate into premature graves within a few years if not culled sooner. Those mix/cross-breds don't contribute too much to resistance breeding, obviously. They don't go far, usually, but that said it's not too uncommon to ship even mix-breds across the country here.

I am not aware of mongrels being shared cross country, and if they are, it is a recent occurrence.

I live in Australia, not the US, lol. It's not a recent occurrence here, we've got chooks from all over Australia being traded and traveled and sold quite regularly; also, from what I've read of the history of the US, mongrels were also traded and sold and traveled long distances as well. Only in more built up areas has this not been so common. People being able to get the chooks they want from nearby breeders is a semi-recent development, which helped slow trade in mongrels, from what I've read.

Still, homebound mongrel flocks are always being exposed to the outside world via new chooks being brought in somewhat regularly, or the owners mingling with other people who also have poultry. The flocks most likely to operate in bubbles are either purebreds whose owners practice biosecurity, and remote landraces. There's always been fixed-location breeders, and customers who order birds from long distances, as well as those breeders and customers which like myself travel birds whenever they move rather than dump the whole flock and restart at the new location. Nothing new there, in fact it's just gotten so much easier to do it in this era.

In Australia, poultry imports were closed early on, and have remained stingy ever since; when people want quality birds in Australia they travel them across the whole country if needs be. Going by this forum and USA hatchery websites, it's commonly done in the USA too, and even if that's not mongrels being traveled, that's still birds which are pretty often carrying diseases being transported long distances, bringing new strains of disease to resident populations.

I am not certain what you mean by all over.There is haphazard trading of birds in my area. Usually it is hatchery stock, and sometimes they are mixed hatchery stock. They are not anymore resistant to disease (as a whole) than any other. The owners usually have more problems with disease, but the problem is usually rooted in the management of these birds.

I don't know what it's like in your area, I was referring to my area. And no, I agree, I don't find hatchery stock resistant to anything much. But they can serve as useful vectors of infection. I think also a distinction between 'mixed' and 'mongrel' is necessary; for example a 4-way crossbred and a mongrel are not the same thing in my usage of the term. Not sure what intended usage it has in your context.

I think your point is valid when you compare extremes. The land raced breeds of tropical Africa are better suited for their environment, than mine would be. Mine are originally from Peru by the way. Still if those land raced birds, if bred to fix type and color, would be no more or less resistant because they were. They would only become more or less resistant if the breeder used birds that were susceptible or more resilient. They are only removed from the gene pool if they die. If they succumb and recover they breed, and if they are resistant they breed. A breeder has the opportunity to remove a susceptible bird from the gene pool. A breeder has the opportunity to make faster progress on this one point because he/she has control over specifics.

I think there's been some misunderstanding of what I meant here. When I referred to mongrels, you appear to have substituted the word 'landrace' instead; I assume landrace and mongrel are synonymous to you, (just judging by your usage of it in response to my previous comments about mongrels), but they are distinct terms to me. Landraces are not managed by people, whereas even neglected mongrels are almost without exception still 'managed' by people, just in an often very slack-handed way.

The points you used with asserting that mongrel flocks would be more resistant could be used for pure breeds to. Some yes and some no. Many do not treat, trade their birds across country, and expose them too many birds at the shows etc. Some of course, do treat their birds and coddle them along. The variation is in the variety of breeders, as much as there is variation within breeds and strains.

Yes, there sure is a variety. In my experience though the breeders of purebreds are often carrying the really weakly birds, whereas those from mongrel breeders don't seem anywhere near so susceptible to anything. But I know this experience does not cover the whole spectrum, only mine; it's pretty hard to define what you mean when you're talking about mongrels in general, though, and those who breed them. You and I seem to have very different experiences of the subject matter and as you say there is a variety.

I think it's significantly different in Australia... We rely on long distance transport in ways some other more densely populated and habitable countries have almost forgotten about. It's not considered a big thing to go driving from one end of Australia to another just to pick up a car one has bought, for example, by most people I know. Most of us aren't so sedentary-minded when it comes to traveling that we'd balk at massive roadtrips for apparently small reward... After all that's kind of par for the course when you live in Australia, especially in rural areas, which is where my experience is based.

Our chooks get around almost as much as we do. I've lost count of how many times I've traveled my chooks now, lol, and how far. We've also traveled other animals all around Australia multiple times. I've known people who literally travel with chooks in their caravans, among other animals. Not saying it's necessarily ideal nor advisable (and probably not even legal) to do any of that, but it's just not considered really 'out there' and strange or anything like that.

(For the record the caravan chooks etc were all in quite decent health, allowed out at every stop, and no, their owners weren't the 'sort' of people who match probably the first dozen stereotypes that may spring to mind for some when considering what sort of character keeps chickens in a caravan while traveling around Australia).

I never intended to say that we could not or should not breed for resistance. I prefer to call it breeding for health and vigor because I want to be realistic with my expectations.

Well, perhaps that's a point of disagreement there. After all this thread is devoted to breeding for resistance and it is indeed a realistic expectation. The very 'health and vigor' you're breeding for is based on resistance to everything that opposes health.

Seems to me that it's a conflict of terminology rather than philosophy.

Best wishes.

 

[speckledhen]

I rather like this entire discussion. Very lively and civil, too. A nice change from some on here, right?

 

[chooks4life]

I rather like this entire discussion. Very lively and civil, too. A nice change from some on here, right?

Yes, it's always good when people can act like adults, for sure.

Best wishes.

 

[speckledhen]

Yes, it's always good when people can act like adults, for sure.

Best wishes.

LOL, so rare! Thanks for your comments on the other thread. Good when someone who knows what they're talking about comments.

 

[seminolewind]

Trident, I'll look those things up and see if there's mention. The one thing I know about Herpes is if a mom is going to give birth to a baby and has an active lesion, they do a C-section so the baby can avoid coming into contact with the lesion. With HIV, it's trickier because the baby is exposed in utero. The baby gets a course of acyclovir at birth. Babies test negative for I believe 18 months before they turn positive but there's a good chance they won't turn at all.

Has anyone in Key West done a study on how long those roosters live?

It is truly a treasure when a thread brings out a bunch of people who contribute their knowledge rather than argue. I remember about 4 years ago people were saying that only the big production companies' chickens get Mareks, and their vet told them so!

Just think, Cynthia, when or if you get blasted, you attract thousands of people to read what you say , which leads to thinking which leads to learning.

When all chickens were mongrels, prior to human intervention, they were hardy to their environment and were not kept in close quarters but small wild flocks. Then humans come along and raise chickens in pens, create purebreds (which takes a lot of inbreeding), meanwhile exposing them to "close quarters" illnesses as their gene pools become weaker as their resistance is not carried by survival of the fittest.

I think in any animal like with mixed breed dogs, their gene pool seems to cancel out a lot of poor genes r/t poor resistance. It's quite a feat when someone attempts to breed hardiness back into their breeding program.

 

[Nambroth]

I apologize for not commenting on this question. I have to ask a few of my own. Well not to you but for you to look up in your book and/or ask an avian specialist.

Is there an antibody titer test for Marek's?
Is the virus shed when it's dormant.
Is using plasma (instead of vax) a possibility in chickens? What route? Is oral acceptable?
Will there be a problem using plasma with "original sin"

If there is a titer test, test the mother and broodmother of your upcoming hatch for antibody levels and an MDV test also. Retest titer in 4weeks to see if antibody level goes up, down, stays the same, and is it at a protective level.

If plasma is OK with chicks AND if mother's MDV -, titer is staying the same and at a protective level AND " original sin" is discussed, pull blood, spin down and give plasma to chicks.
Titer of broodmother should tell you a bit more about if she has an active infection, if it's dormant or clear.

Titer Test: When my vet was making phone calls to have my first Marek's bird tested, she was told several times that everyone has moved to PCR. Which indicated to me that titer testing may have once been used. In short, I don't know.

Virus shed: I am unclear on this as well. The best I've ever been able to find is that vaccination does not change the amount of virus shed, AND that more virulent strains appear to shed a greater quantity of virus: http://www.biomedcentral.com/1746-6148/7/70

 

[gjensen]

I agree that there could be some confusion in the terminology. It does not help that I am not a good communicator.

On your last point. I do not like to use the phrase "breeding for resistance". The reason is that it is subjective. Subject to the pathogen, strain of pathogen, level of exposure, other mitigating factors, the birds that are used, etc.
To do what the phrase says accurately could require a lot of birds, many generations, multiple enclosures, identical conditions, uniform exposure, a control, and a reliable source of the same strain of pathogen for many years. There would be a lot of test mating to demonstrate the heritability of resistance.
Resistance also is used interchangeably with immunity, which would be misleading. Just how resistant is resistant?

Instead I use the phrase "health and vigor", because that is what I am doing. Health and vigor, along with management, goes a long ways towards a bird being more "tolerant".

I do believe that over the years, and from breeder to breeder, that resistance is gained as a result of breeding for "health and vigor". Then the resistance (or tolerance) is limited the condition of the birds and what they have had persistent exposure to. That resistance would be subjective until proven definitively.
It does not make it any easier that the pathogens are constantly evolving themselves.

I used land race breeds to your credit. They best illustrate your point. They would be more uniformly tolerant of local conditions than other birds would be. I have Thai game fowl mixes in Thailand, birds in tropical Africa etc., in mind. Birds in tropical areas that are barely managed and disease pressures are high.
Discussing mixed breeds is difficult because there is no way to know what they have in their background, all of their history, etc. unless you are intimately familiar with them.
It is not all that different with "pure" breeds. Everything depends on what you are getting and who you are getting them from.

Birds do drift towards mediocrity. How fast depends on the variability. It also depends on what you call fast. Still more variability, means faster change. In either direction. If all of the birds in the background were productive layers, then they would be relatively productive for some time. Without any pressure on the traits that make them productive, they will gradually decline.
On the other hand, if I have any variability within a flock, I can make improvements relatively fast. If the flock is relatively uniform, progress will be slow. If the trait is not there that I need, I have to go outside. Then I can make progress again.

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.

Not all pathogens are the same. In this discussion it is Marek's. All we can do concerning selection is to cull symptomatic birds. If we are unfortunate enough to have substantial losses, it becomes a decision whether to continue this practice and/or vaccinate. The vaccination may not give complete protection, but if I am tolerating heavy losses, I may concede. It is hard to make progress if there are no birds to make progress with.
I do not think it is realistic to expect our birds to withstand especially virulent pathogens or strains of.

The birds that are our pets is another matter.