Inbreeding and it's effect on the Immune System

[presas4me]

Interesting article:

Inbreeding Effects on the Immune System

The biggest damage caused by inbreeding is an inevitable reduction in the effectiveness of the immune system. A mammal's immune system is an amazing, intricate, system designed to fight off every potential foreign invader. It is absolutely dependent on genetic diversity. When an animal has identical copies of its immune system genes, the immune system becomes limited in its ability to ward off disease. The end result is an animal that can fight off some diseases very well, but is extremely susceptible to others. This phenomenon is seen in both laboratory situations (there are lists for every inbred strain of mice of what diseases they can resist, and what ones they can't) and in the field in endangered species.

One set of genes whose function is critical for an animal to be able to fight off the variety of diseases that they may be exposed to is the MHC (major histocompatibility complex) genes. These are the genes that mark virtually all of an animals body cells to help the body's immune system distinguish itself from foreign invaders such as bacteria or viruses.

Aside from marking a body cell as "self" these genes provide another essential function. They bind to, and display any foreign molecule (or antigen) to the immune system. This antigen presentation is necessary for the immune system cells to see and respond to an invader. Unfortunately, every MHC protein can only bind to and/or display a selection of antigens. Fortunately we mammals have a number of MHC genes and many versions (or alleles) of each of these genes.

These genes are critical for immune system to differentiate yourself from foreign objects, and for displaying foreign antigens to your immune system. Diversity in these genes is probably essential for a species to survive the variety of disease causing organisms that they may be exposed to.

Let's use a simplified example here. Assume that there are 2 MHC genes, and each has 5 alleles. This can produce a total of 225 different genotypes! AND in fact, in humans there are at least 9 separate MHC class I genes and a bunch more class II genes let alone class III. So far in the 3 most easily studied class I genes, one has 37 alleles, another has 59 alleles and the third 111 alleles discovered so far! This leads to a huge diversity of immune system capabilities in the population as a whole (Kuby, Janis "Immunology" 3rd edition 1997 W.H.Freeman , NY)

This huge variety allows our body cells to respond to a huge variety of antigens, and thus to be able to fight off a wide variety of diseases. An additional benefit of this system is that with the huge variety of MHC genes, chances are that in a given family, mom has one set of genes and alleles, dad a completely different set, and that all the kids each have a unique combination. This way, if a given disease manages to circumvent one family memberís immune system, it may not be able to do so with the other family members.

When an animal is highly inbred, the number of these variations drops dramatically. In our original simplified case of two genes with 5 alleles each, a highly inbred animal would be homozygous for both genes and would make only two MHC molecules. To make matters worse, all of the animals in the inbred group have the same two, so if one animal can't respond to a disease immunologically, none of them can!

An example of the results of lack of immune system diversity can be seen in inbred laboratory strains of mice. (next)


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[eSPO]

Does the article state at what level of inbreeding for how long leads to a reduction in the effectiveness of the immune system ? Lab rats are inbred to an extreme. What qualifies as highly inbred ? The inbreeding of dogs, even highly inbred and linebred game dogs, American Eskimos, and geologically
isolated species doesn`t begin to approach these extremes.

[surfnplay12]

How about sombody write an article about how not linebreeding effects temperment :D .

[kaner6]

The article is dead on about alleles and genetics. The simplification is really that...a gross simplification but it does a good job at explaining the genetic determination of the immune system.

This is why if there is going to be line breeding and inbreeding, it should be done responsibly. Outcrossing, Culling and taking dogs that show certain genetic issues out of the gene pool.

I would never say that I am totally against line breeding....even really tight line breeding. If I did that I would have had the opportunity to own my pit.

That being said I am not about people line breeding if they don't have an idea about phenotype/genotype and can be honest enough with themselves to take the necessary precautions as to not allow crap to get out there.

Justin

[surfnplay12]

NO I agree totally justin but the key is culling. You can make sure and get rid of the traits that don't need to be passed on and only select best wether its one or four doesnt matter. Linebreeding is the only way to get consistent results and improvment in your breedings. Because you can consintrate the traits that you like in everybreeding instead of taking a chance on an outcross when you have no idea what traits are going to pop up.

[kaner6]

this is why on the outcross if you understand the genetics of phenotype/genotype you are doing the best of keeping the gene pool a little wider and still getting what you want.

This is an example from a guy in the bulldog world talking about Johnson Dogs (I have no clue about the bloodlines but from what he said it sounds like a valid point).

The Johnson Dogs have the shorter muzzles but they also don't have the most enormous gene pool. He explained that natural selection would select for a longer muzzle for functionality. So now you see the Johnson dogs beginning to have their muzzles elongate because of the progression from generation to generation of breedings.

You can than use that with the Presa's. There isn't that large of a gene pool (here in the states at least) to work with. The tighter and tighter you breed the more likely you are to get undesirable traits concentrated in the litters. Culling will only take you so far...you can't cull an entire litter and have anything left to work with. What I am saying is there needs to be outcrosses. Just outcross to a dog with the traits you like and do your research and then you keep your breeding coefficient lower.

I apologize if I am totally off with the Johnson Dog reference but it made sense when I heard it.

Justin

[eSPO]

Inbreeding, linebreeding and outcrossing are all valuable tools for the knowledgable breeder to use if his desire is to truely improve his stock.
The outcross is a tool that maintains diversity but gives no guaranties and is more like a good rubber hammer, dull , effective, general and relatively safe. Linebreeding is a safe way to maintain valuable characteristics and get a little more specific results, it is like a ball pean hammer, hard, effective, less general and relatively safe. Inbreeding is the best tool to perpetuate the most exact copy of what you want. It is sharp,specific, and more dangerous in the hands of the novice. Understanding the pedigree, knowing the health of founding members, their coefficients, and having a concrete goal are mandatory for all three and more critical the tighter you go. Culling is mandatory for all three, and more critical the tighter you go. Not culling a bad pup out of an outcross is bad, not culling a bad pup out of a inbreeding is even worse. Luckily mother nature has preventative measures and seldom are her barriers approached. All good, serious breeders should experiment as long as they can deal with the good, the bad and the ugly results in the appropriate fashion. ( I am not speaking of breeders that don`t understand it of are afraid of it, to me these are not good breeders)
Justin, sometimes i`m not so sure the talk of a limited gene pool is a little overblown when it comes to the Presas. There are so many different breeds and combinations of them and different lines of the same breed
present as well as a drawn out founder event . I feel there is plenty of diversity out there even if the over all population is relatively small. Just a thought.