Moving Forward- Breeding for Resistance to Marek's Disease

[Nambroth]

I would like to leave the PCR info for Nambroth because she has more information than I do, and I worry about passing on incorrect information. I know that there can be false negatives , but false positives are rare. A PCR is one test that may pick up an exposure that is not seen by a pathologist .

From what some of us have read or found, Marek's not being the only one to depress an immune system, but I've had more coccidiosis , a few necrotic enteritis (dropping dead no symptoms except a dead bird who bled out), a few of mine seemed to get a one eye infection, look sick, and die before I could start treatment. With the enteritis, now I will treat forever for coccidiosis and enteritis together with Corid and Tylan, which can be given together. These were all under 10 weeks old.

I should start a notebook as well. I think I can put most of it together with the dates on pictures.

I know with work it can be real hard to see your chickens, but sometimes I can run out there in my pajamas and a flashlight and just eyeball them quick.

I think you have it pretty well covered. PCR stands for polymerase chain reaction, which is a fancy way to say that scientists have found a way to make certain chains of DNA replicate themselves so that they are easier to isolate. These DNA markers are specific to species, meaning, they can isolate the DNA of Marek's virus and thus see if it is present or not. This is a very simplified layman's explanation, and I am NOT an expert or even very well versed in this technology.

False positives are thought to only occur on occasion if a chicken has been vaccinated with Rispen's vaccine, which is only available at a few commercial hatcheries at the time I am writing this. If you have hatchery birds, and are unsure, please call the hatchery where your birds came from and give them a date you bought them and they should be able to tell you what vaccines were used (if you bought vaccinated birds). This is because Rispens vaccine uses a (safe) virus that might be able to cause a positive hit on a Marek's PCR. In short: A bird that has NOT received a Rispen's vaccine should never have a false positive. A positive means that the virus is present. Period.


False negatives are more likely, especially if 1) non-reactive tissues are sampled (meaning if the bird is not showing signs and/or a blood sample alone is used) or 2) The bird was latent at the time samples were collected.
Testing of suspect tissues, such as organ tissues where tumors or lesions were found is generally going to have the most accurate PCR test, especially in real-time PCR (qPCR). Unfortunately, this requires a deceased bird....

The blood test is better than nothing, but if the bird is latent (a carrier but not actively symptomatic) there is some concern that the virus concentration is low enough that it won't be detected.
This is all quite complicated, and should be used as a tool, as part of the puzzle.

 

[chooks4life]

Anyone that says that it is easy, has not done it.

It is not especially complex, just requires a real commitment and a stomach for it.

Seems the statements above are contradictory to me, but maybe I'm missing your intended point there.

I disagree with the universal statement you made first, for obvious reasons; it simply cannot possibly be correct nor proven.

It is also not as if it has not been done countless times. There is a huge body of work on the subject dating back to the 20s-30s. There was a lot of work done on it in the 40s-50s. The creation and popularity of vaccines quieted a lot of it down. Now most truly resistant flocks are found in research centers. It is just a matter of insuring even exposure, killing symptomatic birds, proving the parents by way of their offspring, and selecting symptomatic individuals that came from non symptomatic individuals and had the best % of un symptomatic offspring.

I agree with all that.

You and I possibly would agree on one point, and that is I think we would have been better off had the vaccine never been made. Economically we would have suffered large losses, but we would have been better for it in the long run. We would have worked through our problems along the way. Even if we had lost some breeds in the process.

Yeah, I reckon we definitely agree on this point.

I do wish that I had the resources to take on a number of projects like this. It would be interesting to do. There is no economic incentive to do it because there is not enough demand to pay for it.

It truly is a shame that those with the interest lack the financial wherewithal to invest in research.

You and I often don't see eye to eye on many things, but that's a good thing; it goes without saying that the the more people approaching the situation with the variation of viewpoints on it, the more likely the solution is to be found.

Best wishes.

 

[seminolewind]

Quote:
I can only go by what I've experienced. Most of the time, if they show signs of coccidiosis they get treated. I had 3 eight week old birds that died overnight with no symptoms the day before, and blood ran out of them when I picked the bodies up. They had always been in one pen and no one was added. They were vaccinated for Marek's.

Panicked, I gave them an anticoccidial and Tylan because the (non) symptoms and hemorrhage didn't completely fit, and they did fit for necrotic enteritis. The Tylan is what probably saved the rest. Probably. Because 3 years later now, I've sent 3 necropsies that have all shown enteritis of small intestine and one of liver necrosis as well. Tylan is drug of choice for necrotic enteritis.

So based on that history, and the age of the last 3 birds, (about 5-6 years old) I would do both.

 

[seminolewind]

Quote:
There were approx. 80 years without the vaccine and wouldn't that have been long enough and tried many times to breed for resistance? Prior to the vaccine (in the 80's ?), losses were up to 60-80% in the chicken industry. Based on that I feel that there had been plenty of time to breed for resistance and have it work. I'm sure that this must have been 80 years of economic incentive and the numbers only growing higher.

 

[chooks4life]

There were approx. 80 years without the vaccine and wouldn't that have been long enough and tried many times to breed for resistance? Prior to the vaccine (in the 80's ?), losses were up to 60-80% in the chicken industry. Based on that I feel that there had been plenty of time to breed for resistance and have it work. I'm sure that this must have been 80 years of economic incentive and the numbers only growing higher.

It does beg the question, for sure, but it's impossible to say what went on there.

Numerous studies found resistance was quickly achieved when breeding for it, so what happened after that? I suspect the very type of bird they needed for economical reasons was directly contrary to the sort that was resistant, and when it seemed the vaccine would provide the solution, they abandoned the longer-term task of breeding resistant strains back to economical standards. Just a theory obviously, but why else would they repeatedly abandon what they showed were successful trials in breeding for resistance?

I think they probably found those resistant birds were simply not able to be bred into such economically viable types as the susceptible ones, after all, many of the best meat bird strains have thinner gut walls, allowing greater penetration of bacteria and other 'nasties' thus making them more susceptible to disease of course, but which also enable them to grow quicker and be more feed efficient by allowing more rapid uptake of nutrients.

It's hardly a trait that can serve both the bird and the economy. Breeding that trait out would indeed make them more resistant, but also make them less economical.

Perhaps they were unable to separate the two traits, or other interlinked traits, and simply gave up and put all their faith in vaccines. That's my bet. Every new vaccine that came out, they thought had solved their problem permanently.

Certainly, with mongrels etc, MD is not the terror it is to commercial strains, it's not like breeding for resistance is impossible or even really difficult, just that it doesn't suit some operations.

Best wishes.

 

[chooks4life]

One further point that I think supports that theory is the fact that Leghorns are often touted as being MD resistant, and since they're not bred for such rapid growth nor known to have that thinner gut trait, it seems likely to me that the MD resistant Leghorns we read about in some trials were perpetuated, whereas I've heard no such equivalent of the meat bird breeds of MD resistance trial subjects. Never hear Cornishes being referred to as MD resistant even though they were successfully used in some trials, for one example.

Course, it's just a theory.

We know they developed resistant strains, what we don't know is why they abandoned them. Something happened, and given the industry's repeated returns to vaccines, I think that was probably it... They kept trying what must have seemed the easy and permanent cure, but which was obviously not any such thing.

Best wishes.

 

[lalaland]

I can only go by what I've experienced. Most of the time, if they show signs of coccidiosis they get treated. I had 3 eight week old birds that died overnight with no symptoms the day before, and blood ran out of them when I picked the bodies up. They had always been in one pen and no one was added. They were vaccinated for Marek's.

Panicked, I gave them an anticoccidial and Tylan because the (non) symptoms and hemorrhage didn't completely fit, and they did fit for necrotic enteritis. The Tylan is what probably saved the rest. Probably. Because 3 years later now, I've sent 3 necropsies that have all shown enteritis of small intestine and one of liver necrosis as well. Tylan is drug of choice for necrotic enteritis.

So based on that history, and the age of the last 3 birds, (about 5-6 years old) I would do both.

hmm. that's valuable info. I'm putting it in the notebook.

 

[seminolewind]

I got interim #3 report. On a sample of liver tissue they found moderate growth of e. coli and staph.

I think I could just put the last 5 demises in a category of opportunistic bacteria or fungus due to a poor immune system due to Marek's. These were all older birds (5-7) , survived Marek's as adults, but when it's written that Marek's knocks their immune system out, I guess it doesn't matter if the bird is symptomatic or not, they still get their immune system almost wiped out.

OR does this stuff happen with older age, is this dying of natural causes?

I found a packet of Broiler Booster that is vitamins and probiotics in one. It's given at a 1/4 tsp per gallon. It came from MMc.

 

[lalaland]

I hate it when a report makes me have more questions than it answers. What is "moderate"? enough to kill them? not enough to worry about? I would be surprised if there was no staph and no e.coli, wouldn't you?

My oldest hen right now is either 6 or 7, I start to get confused about the years, lol. I heard someone say they had a 12 year old hen, that seems crazy to me. I wonder if it just like humans, where you might die of pneumonia, etc - in your 80's, 90's, etc.

 

[Nambroth]

I hate it when a report makes me have more questions than it answers. What is "moderate"? enough to kill them? not enough to worry about? I would be surprised if there was no staph and no e.coli, wouldn't you?

My oldest hen right now is either 6 or 7, I start to get confused about the years, lol. I heard someone say they had a 12 year old hen, that seems crazy to me. I wonder if it just like humans, where you might die of pneumonia, etc - in your 80's, 90's, etc.

A friend just lost their last black cochin hen earlier this year. She was 13. She was a crunchy old lady of a hen, but she was genuinely 13!