Inbreeding Question

[Tuffoldhen]

Quote:
Yep, This is how it is done.

 

[hinkjc]

http://www.poultry.allotment.org.uk/Poultry/Start_Keeping_Bantams/bantam_chicken.php

Jody

 

[kinnip]

I've been researching linebreeding and inbreeding for goats as well as chickens. I don't think there's another subject with more opposing opinions. No one seems to be able to settle on a common definition. I think it's because "linebreeding" isn't taboo like "inbreeding". I stopped arguing over the semantics of it. It's what I'm doing and I don't care what anyone calls it. In fact, I think I'll just come up with my own word, but I doubt it'll be one I can present on a family forum.

 

[fowltemptress]

I did research it over all the conflicting views I was seeing, and linebreeding is through family members in the same line, not direct father daughter and sibling relationships. The term is often adopted by agricultural breeders whose animals are bred through inbreeding, and like the purple martin and mosquito myth, is now accepted as a general fact. Even though it's technically incorrect, I do think it was a good idea for breeders to twist the definition in order to attract more urban dwellers to the idea. "Inbreeding" is not a word that sits well with many people, even though it is a fact of agriculture.


It doesn't matter much, anyway. Language is such that eventually enough people will think linebreeding involves parent/offspring and siblings that the definition will effectively change to fit the common usage, like with the word awful. Just wait long enough and Tuffoldhen's and NYREDS' definition will become the correct definition.

 

[brandywine]

Geneticists recognize one term -- inbreeding.

The degree of inbreeding is expressed mathematically as a percentage, called the Coefficient of Inbreeding (COI). A meaningful COI is generally regarded as requiring a complete ten-generation pedigree. The lower the percentage, the more heterozygous the animal is. Of course any pedigree-based computation is only an approximation, as there may be more background inbreeding than revealed in ten generations -- there may have been a genetic bottleneck in the population prior to the individuals in the pedigree.

Different species have higher or lower thresholds for inbreeding depression. For example, cheetahs, which as a species have undergone a number of severe genetic bottlenecks, have uniformly COIs/homozygosity, and seem to tolerate this better than other higher mammals. Regardless, the higher the COI, the less vigorous, fertile, healthy, and long-lived the animal. This is a general rule of population genetics. High COI's are common in "fancy stock" of various species, like poultry, mice, show dogs; with few exceptions (Holstein dairy cows come to mind) they are almost unheard-of in working and production animals. The loss of vigor, fertility, and general health is far more harmful than the consistency that comes from homozygosity is useful.

Repeats of a single ancestor in a pedigree are expressed with the ancestor's name and numerical notation. So, for example, the grump Umsa von Bungalow is both a great-great-granddam and a great-great-great-grandam of my own GSD; on Sophia's pedigree, this "linebreeding" is notated as "Umsa von Bungalow 4-5" -- indicating her presence once in the 4th generation and once in the 5th generation. (This is, btw, a typical degree of "linebreeding" in a working-bred GSD. A show dog would typically have several ancestors repeated several times, closer up in the pedigree -- it might look like this "Ch. Wobblyhocks 2,2-3-4" indicating that Wobblyhocks was both grandfathers -- i.e., parents were half-siblings -- and also a great-grandfather and a great-great-grandfather.)

You can call frank inbreeding -- parent/offspring -- anything you want, but it doesn't make it "not inbreeding." Nor does it inoculate the offspring against the debilities of homozygosity -- which are NOT limited to "doubling up on defects." The immune system hates homozygosity. Inbred populations are always relatively less healthy, viable, fertile, long-lived, and generally functional than heterozygous populations of the same species.

That's half the reason for the black stars in the first place. The specific cross makes them color-sexable. The fact of the outcross makes them vigorous and productive.

 

[kinnip]

Quote:
I understand the mechanics of it all. I just love to see a wrecked pile of reality tunnels.

I'm curious, why does the immune system "hate" homozygosity if homozygosity hasn't done anything to it? Wouldn't this collapse be the result of "doubling up on defects"? If not, what is the specific reason for this flaw?

 

[brandywine]

Quote:
It's not a flaw, it's the way nature works. Sexual reproduction provided an evolutionary advantage to those creatures who first evolved to use it because of the power of recombination to shuffle out a hand that is better-adapted to a current environment, or to a novel challenge. Severe inbreeding cancels out that advantage

If I knew why, specifically, the immune system hates being homozygous, I'd find some way to get rich in biotech.

But the best general reason is that having two different copies of any given allele provides more insurance that one of them will be the one that codes for resistance to any given specific environmental challenge.

Multiply that by a gajillion genes per organism, and you get a general result in the whole organism -- tough, thrifty, long-lived, resistant to disease and neoplasms vs. delicate, short-lived, disease and cancer-prone. Since entire organisms reproduce, not individual genes, one cannot effectively select for homozygosity for a single trait (especially a rare trait) without getting an animal that is homozygous for many more genes.

This becomes even more murky when one is selecting for a single quality that is governed by the interaction of many genes + environment (say, very high egg production).

And rigorous selection for a suite of recessive fancy traits (say, slate gray legs, spangled pattern, rose comb, black and white coloring, tinted eggs, and face muff) is not only quite difficult, it pretty much requires severe inbreeding to achieve homozygosity for all the recessives -- guaranteeing generalized homozygosity for all the animal's traits.

That's why F1 hybrids are so popular in agricultural production (animals and plants, many species). The highly inbred parent stocks are consistent but "depressed." Breeding stocks often have to be coddled along. The carefully selected first generation crosses show not only consistent recombination of traits from the parent stocks, but "hybrid vigor" from the heterozygosity.

Performance animals, such as working dogs, are generally selected via assortative mating -- in which animals that are phenotypically similar for the desired traits, but genetically relatively unrelated -- are mated. Results are less "consistent" than with inbreeding for fancy traits, but are clearly better in terms of offspring being healthy, vigorous, mentally sound and useful.

My own working dog breeding program has, over the past six years, produced 18 healthy puppies with a fair variety of sizes, colors, head shapes, and a range of personalities -- but all have had great working ability and solid temperament.

Since I'm not interested in coddling farm animals, my breeding strategy for poultry (and next year, sheep) excludes inbreeding, and further, relies on culling out weak or unthrifty animals. For example, I won't save hatching eggs from my "pet" NH hen who had crooked toes and needed intervention, or from the guinea who needed treatment for an impacted crop. They are welcome to stick around and contribute eating eggs, but they are culled from the gene pool. I'll keep replacement ewe lambs only from dams who birth without assistance and produce twins or triplets in their second and subsequent pregnancies, and who don't require worming or antibiotics.

 

[DTchickens]

father/daughter/grand daughter etc, doesn't matter, nor does mother/son. i have done it loads of times. and its a good way to maintain the line. and not add in any unwanted blood. or cross brother/sister which bring up bad traits. also.. say you have a bloodline. everythings dead but this mother/father, with their crossed son, or daughter. you can take the offspring. and breed back to the mother/father.. and take the offspring out of that, and breed it to the (grandparent/parent). For 6 generations. and you will have EXACTLY what that parent is, as if it were their sister or brother.(or so i hear). but dont do it anymore then that. as then it will just get horrible, from there you take the offspring from that and breed it to the mother or something. never the father again.

-Daniel


PS. not sure if this is true. just the info i've gotten from about, 20 people, numerous sites and forums. etc. from experienced poultry breeders that have been raising poultry for YEARS. around 30-40 most. and if i didn't think it was true. would have never said it. not that kind of person

 

[kinnip]

Quote:
This is pretty much what I meant. Nothing happens for no reason, and with ruthless culling inbreeding can work. I would love to go with a true linebreeding program, but due to my limited resources, there will certainly be some father/daughter crosses in the first few gen. This is why I went to a lot of trouble to insure my goats were from diverse gene pools, stretching across three states. The chickens will be a little trickier since I don't have pedigrees on any of them, I'll just have to keep a close eye out for anything undesirable and cull, cull, cull. I intend to slowly introduce any new blood. I know it's difficult sometimes to see the genotype, but until it expresses, It's not in my purview. Unexpected and unwanted genotypical characteristics can form in any breeding, be it from unrelated individuals or not. The narrower ones scope when choosing for characteristics, the more likely you are miss something important, I think we agree on that. The characteristics I'm most interested in selecting for are those that are usually not well supported in a failing overall genetic scheme. Intelligence, ranks very high on my list of desirables, followed by disease resistance and production. I don't intend to let everyone turn fugly as that might hurt my chances of selling them. Ultimately, I view it as an exercise in patience and perception. I think we agree on the mechanics, by and large, just not the wording. I'm simply not content to say it happens 'because'. It's something that can be quantified and controlled.
Nice conversation, BTW. I look forward to the next one!

 

[Lee]

I have wondered about this. Say, you start your flock with some hatching eggs. You wouldn't want to save a rooster from that batch would you?