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#28841 - 12/23/05 07:49 AM Re: Carefoot on Breeding Brother x Sister 20 generations
BC Breeder Offline
Coop Keeper

Registered: 07/16/02
Posts: 434
Loc: Canada
That is an excellent article by Caveny, I follow a similar principle when getting a rough impression of the inbreeding my flocks are being exposed to.


As for Ron O's article, there is one statement that suprised me.

"Chickens probably do not line breed very well. They have about twice the genetic load as other animals like humans. "

I find it counter intuitive to think that chickens would have twice the genetic load as humans. Basically, historical breeding patterns determins genetic load. Animals that tend to inbreed tend to end up with lower genetic loads than animals that tend to outcross. Humans throughout most of it's history have tended to outcross, we tend to avoid mating within the family. On the other hand, chickens since their domestication have tended to be inbred. Line breeding and sibling matings are common. With each and every successful generation of inbreeding, the genetic load is reduced. When refining a line, the outcross is the exception to the rule. Therefore, one would expect a chicken to have a lower genetic load.

And this is most evident with our most inbred commercial chicken line, the white leghorn. White leghorns are so inbred that they are practically clones, LOL. They are also documented as being the most resistant to inbreeding techniques and having the lowest genetic load of the chickens.

does anyone have any references supporting Ron's comments?

With that said, I do agree with Ron that chickens don't line breed as well as other animals. For the purpose of this discussion, I think of line breeding as the backcross to a superior individual. One of the strengths of the backcross is that your co-efficient of inbreeding tapers off after the 3rd backcross generation. Unfortunately, it's hard to get 3 or more backcross generations from a single chicken, most end up dying or getting killed before one can cross them with their great grandchild, let alone getting to their great great grand child.

On the other hand, it works well with cattle because one can get 20 generations from a good cow or bull. Without AI, nonetheless.
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#28842 - 12/23/05 09:05 PM Re: Carefoot on Breeding Brother x Sister 20 generations
Longhackle Offline
Feather

Registered: 11/11/05
Posts: 29
Loc: Arkansas
BC Breeder, pertaining to the first part of your message, I was thinking the same thing.

However, with more vigorous strains of chickens like some of the Game Fowls it should be easy to get several generations of backcrosses to an individual, as these birds typically are very disease resistant and reproduce very well for several years. Also a bird that is of superior quality is normally kept in a secure pen where predators cannot get to them. I have heard of instances of breeders backcrossing 6 or 7 generations of offspring back to a certain individual. I had a friend who bred the daughters back to a certain cock for 12 generations.

One must consider that in cases where the superior individual is hetero and not inbred then theoretically the inbreeding is not suppose to exceed 50% inbreeding even after several successive backcrosses of offspring back to that individual, though it seems there would not be as much consistency accomplished in the offspring if the superior individual was not homozygous.

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#28843 - 12/28/05 07:59 PM Re: Carefoot on Breeding Brother x Sister 20 generations
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2792
Loc: Australia
BC,
The following is a quote from ROKIMOTO, from a previous thread, which will help with your query on human genetic load:


The Coop: Inbreeding2
Quote:
Inbreeding is the only way to purge detrimental alleles from a population. The less inbreeding that occurs in a species the higher the genetic load. This happens because recessives can build up in a population if they are never made homozygous. If you never inbreed, detrimentals can reach a higher frequency in your population. Chickens probably have a lower genetic load than quail because they have been domesticated in small local populations for 10,000 years and detrimentals have been slowly selected against.

Humans have a pretty low genetic load. It is estimated to be less than half what it is in chickens (around 2.5 instead of 6). Modern humans seem to have had a population bottle neck around 100,000 years ago where the world population may have dropped to only around 1000 effective individuals that can account for all the humans that we see today. Humans have about 1/5 the genetic variation that you find in chimps or just about any other species. It is sort of scarry, but back 100,000 years ago humans may have been just as endangered as most of the great apes are today.

Until recently inbreeding was common in small villages and hunter gatherer bands. This is thought to have kept the genetic load low in humans.
Longhackle, I had a quick look through Carefoot's "Creative Poultry Breeding" & his chapter in Crawford's book (which is very similar to a chapter in his own book), but couldn't find the quote you were after. The closest I found was the following:

Quote:
Mathematical formulae have been evolved to measure the coefficient of inbreeding present in a particular bird, but these are irrelevent to the poultry fancier - all he wants to know is how close can one go without losing vigour?

There is no general answer to this question. Brother to sister matings have been carried out over many generations, indeed up to seventy with rats, without any observed weakening effects, whilst matings of cousins have produced a strain of weaklings within a few years.
* Carefoot gave me the impression that he really wasn't into line breeding as a general, everyday practice (although he gave examples where the principles could be used effectively). He just selected from the best, balanced the breeding pen with complementary birds, & if there was a choice between two birds with equal points, he would chose the most distantly related to pair with.

I do remember reading somewhere of Ron's experiments/research with chicken inbreeding, but didn't find the post after a quick search. It might be at the old forum.

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#28844 - 12/28/05 08:41 PM Re: Carefoot on Breeding Brother x Sister 20 generations
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2792
Loc: Australia
OK, here is one thread on the old forum which touches on Ron's chicken inbreeding depression project:
http://www.the-coop.org/wwwboard/discus/messages/15/5271.html

ROKIMOTO:
Quote:
I have an Inbreeding depression project where we have backcrossed daughters to sires from a random bred population. We started with 10 sires, but produced enough daughters for the experimental design for only 7. All sires had hatchablities of less than 60% by the second backcross (F=0.375). Most of them less than 30% with two sires at around 11% hatchability. This isn't very good data for most of you trying to breed small populations and maintain production traits.
The following are responses to questions on his project:

Quote:
We know in our inbreeding study that the hatchability difference is due to the males because we breed some of each males inbred daughters to the other males in the study as control crosses and there is a small decrease in hatchability due to the inbreeding of the hen, but quite a lot more if you breed a daughter to her father. Hatchability of a poor sires daughters might be 60% with other males, but only 11% with her sire. As you inbreed the inbred hens do get reproductively weaker, but one outcross can pretty much remove that weakness. I have an inbred line that hatchability is 30% within line crosses, but outcross matings have a hatchability of over 80% with the same hens.

-----------------------

The simple explanation for hybrid vigor is simple dominance over recessive detrimentals. Each line has it's own frequency of certain recessive detrimental alleles. If two lines do not share the same recessive detrimental alleles they will show hybrid vigor when you cross them. You can think of it as one line being AA bb CC DD EE ff and the other being aa BB CC dd EE FF so when you cross them you don't see the detrimental effects of bb ff or aa and dd in the hybrid (Aa Bb CC Dd EE Ff). This is why subsequent progeny from commercial hybrids are on average less productive than their hybrid parents. The recessives begin to segregate in the progeny. The increased genetic variance that you observe in the progeny of the hybrids is a measure of the non additive genetic effects (dominance and gene interactions). What you see is that the hybrids are much more uniform in egg weight and rate of lay than the progeny produced from these hybrids. You will get some good birds, but a lot more stinkers.

The alternative explanation is overdominance, but genetic tests indicate that overdominance may have a minor effect in hybrid vigor, and that most of the effect can be partitioned as the result of simple dominance. Overdominance is when the heterozygote Aa is superior to the homozygotes aa or AA. This seems to be relatively rare.

Outcrosses are less likely to produce the homozygous recessive detrimentals and 1/4 of the inbred progeny of any sire would be expected to be recessive homozygotes for any detrimental allele that he carried. Any one chicken carries a lot of recessive detrimentals. Each human carries an average of 5.

-------------------

Info:

You are right about the inbred males and female testing. The males in our study were not inbred, but only their daughter were, so we measured the decrease between sire and daughter and the daughters with other relatively unrelated sires. Some sires were low with control hens, but not as low as they were when they were crossed to their daughters.

Inbreeding does affect the males, but we had inbreeding data for the females. We were not working with inbred males. We have an inbred line that the male fertility is not very good mainly because we have trouble getting semen from these males. They are all consistently bad. I put one male in a pen with unrelated females to see if natural mating might be better, but I hardly got any fertile eggs. This wasn't a good experiment, but the males are consistently poor semen producers. Part of being inbred is that you are pretty uniform, all the hens look about the same and so do all the males. I've let this line lapse, but when we had them caged together it was like looking at a line of clones. The line is 99.99% inbred and was developed using full sib matings and is kept inbred by mostly cousin matings.
------------------
EDIT 2009 - updated link

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#28845 - 12/29/05 08:08 AM Re: Carefoot on Breeding Brother x Sister 20 generations
BC Breeder Offline
Coop Keeper

Registered: 07/16/02
Posts: 434
Loc: Canada
Kazjaps, thanks for taking the time. I've read that argument from Ron in the past, think I have seen it in Crawford's book. Still doesn't address my concerns though.

Yes, humans were bottlenecked to a population of roughly 1000 effective individuals roughly 100,000 years ago, for the sake of simplicity, I won't argue the point.

This means that the human population has had roughly 6500 generations to re accumulate mutations, thereby increasing it's genetic load. I too am aware of tribes that practice inbreeding, but what effect have these tribes had on the dominant genepools of the globe? We need to be considering the ancesters of today's main genepool, not the remote and obscure genepools.

While the human population was bottlenecked to roughly 1000 effective individuals, most chicken breeds have been repeatedly bottlenecked to a much smaller number, often less than a hundred. Since these bottlenecks, chicken breeds have not had thousands of generations to re-accumulate the genetic load. And most have been subjected to relatively heavy inbreeding since, therefore making the accumulation and persistence of genetic load difficult.

Now I have read other reputable sources say what Ron O has stated so it may very well be accurate. However, it's still counter intuitive and their explainations don't seem to make any sense. Me thinks that they haven't collected data or assessed it in such a way as to give a clear picture.

In the past, this site has been unfriendly towards those who question the ideas of reputable sources. Sheep mentality. However, most advances and new discoveries occur when the accepted is questioned.

Chickens have been subjected to much narrower bottlenecks and much more inbreeding than humans and therefore SHOULD have a lower genetic load.
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#28846 - 12/29/05 09:18 PM Re: Carefoot on Breeding Brother x Sister 20 generations
Longhackle Offline
Feather

Registered: 11/11/05
Posts: 29
Loc: Arkansas
KazJaps, After I thought about it more I think where I read that info about breeding 20 generations of brother x sister was on another message board where someone was quoting a segment from Crawford's book not Carefoot's, but I could be wrong and my memory may be failing me, as it has been a long time since I read that info. It may have been someone else besides Crawford or Carefoot. This has been a good discussion anyway.
Thanks for looking for the info.

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#28847 - 01/19/06 01:08 PM Re: Carefoot on Breeding Brother x Sister 20 generations
Longhackle Offline
Feather

Registered: 11/11/05
Posts: 29
Loc: Arkansas
Quote:

From the old Onagadori board came this advise
From: Ron Okimoto
On Line Breeding

Chickens probably do not line breed very well. Once the inbreeding coefficient goes over 0.375 the lines tend to fail to reproduce one male and one female to continue the line.

So inbreeding in chickens is not a very good thing to do a lot of.

.
I know Okimoto is a knowledgable guy when it comes to chickens, but I do not agree with that statement.

Situation # 1: Daughters bred back to the original male after he is bred to an unrelated
female. Percents are the 'in-breeding coefficient'.

1st daughter = 0%
2nd daughter = 25%
3rd daughter = 37.5%
4th daughter = 43.7%
5th daughter = 46.9%
6th daughter = 48.4%
7th daughter = 49.2%
8th daughter = 49.6%

I have heard of an awful lot of instances where the daughters were bred back 6 times or more to the same sire and were still very productive.

One example of many: Tommy Inman tried to purchase BB Red Old English Game Bantams from Jack Yoder back in the 70's or early 80's, but Yoder would not sell him any because they were in the same showing area in the Carolinas.

Later Inman came across an outstanding Yoder BB Red OEGB male at a flea market and purchased him for a only a few dollars. He wanted to form a pure strain of this line but he had no Yoder females to breed with the male. So he went back to a flea market and purchased some cheap BB Red females of questionable quality and bred them to the outstanding Yoder male and then top-crossed (graded up) by breeding the daughters back for 6 successive generations. That's 48.4 % inbreeding and the line continued to reproduce well for several years and still does as far as I know. I had some of Inman's BB Reds back in the late 80's/early 90's and they reproduced better than most OEGBs I've seen.

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#28848 - 01/19/06 06:09 PM Re: Carefoot on Breeding Brother x Sister 20 generations
Chook-in-Eire Offline
Coop Keeper

Registered: 05/20/05
Posts: 733
Loc: Ireland
Interesting how different the experiences and opinions are.
My own experience has been the opposite of what Longhackle describes. I hatched 1,3 and 1,2 of two related lines (could not get info on exactly how closely related they are) from the same show breeder two years ago.
Myself and two friends set a total of 20 or so eggs of these, in 2 different incubators and under 3 broodies between February and July of 2005. Not a single chick hatched while the 2 cocks proved fertile with other hens they were joined up with (they produced 17 fine, healthy chicks) and the respective hatches yielded other chicks as normal. I have yet to test the hens with other cocks but looking at the results I strongly suspect that they are very much inbred.
chook

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#28849 - 01/20/06 07:56 AM Re: Carefoot on Breeding Brother x Sister 20 generations
Longhackle Offline
Feather

Registered: 11/11/05
Posts: 29
Loc: Arkansas
chook-in-eire,

I have had my share of bad experiences also. I can recall at least 4 instances where I purchased trios of Black Old English Game Bantams for big bucks from well known breeders who were big time show winners and either the females would not lay eggs or the eggs would not hatch. I suppose those must have been too far inbred. I finally learned my lesson. I will not pay big bucks for Black Old English Game Bantams because of my bad experiences, and I don't want to get burned again.

My point was not so much that inbreeding never causes problems, but that if you start out with very productive, vigorous birds I think you can inbreed farther than some people may think before having problems.

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#28850 - 01/20/06 10:55 AM Re: Carefoot on Breeding Brother x Sister 20 generations
CJR Online   content
Coop Master

Registered: 07/16/02
Posts: 8483
Loc: Montana
It was asked about Carefoot and breeding brother and sisters......was waiting for the Dr. this morning (I usually take Carefoot with me) and this morning noted this:

"..he wants to know how close can one go without losing vigor?

There is no general answer to this question. Brother to sister carried out over many generations indeed up to seventy with rats, without any observed weakening effects, whilst matings of cousins have produced a strain of weaklings within a few years."

Maybe this is the passage remembered. If I find another in the weeks of waiting at the Dr., I will bookmark! CJR

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