InBreeding?

[eggdd]

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i think that's great info.

we bred them and hatched out a couple hundred chicks a good solid half of them were deformed, most only had one eye

yikes. is this common? is that what people mean when they say to be "prepared to heavily cull"?

also, i have a question about the trio breeding. when this happens, you are breeding father to daughter? mother to son? sister to brother? or all of the above.​

 

[AquaEyes]

What a "line" really is is a family that consistently produces offspring within a narrow range of variability. For people who show animals, this is desirable, because, in essence, you "know" what's going on genetically and can make predictive matings. What happens is that in outbred animals, there is a great deal of heterozygosity -- in other words, there are a lot of genes that are had as two different versions in the same organism. The dominant version will show in the phenotype, and the recessive version will remain hidden. With outbreeding, the chances that an unrelated individual will have the same hidden recessives is less than with related individuals. So the negative effects of those recessive genes being expressed (and thus being had homozygously) would be prevented by random outbreeding versus inbreeding. However.....


If you wish to establish a new line, you start with a few individuals that have characteristics you desire. By inbreeding their offspring, you will find a lot of individuals early on that express those hidden recessive traits. These are purged from the breeding population (i.e. culled). You keep only those which continue to possess the desired traits in the parents. By switching around the partners, you can find out which pairings give more desirable offspring than others. What this does is indirectly tell you which individuals do not carry a negative recessive trait (remember, for each trait that is heterozygous in the parents, 1/4 will be homozygous without the trait...if you find two homozygous birds without the trait and breed them, none of their offspring will have the negative trait that was carried in by the original unrelated parents). When you get to this point after enough generations, you are producing cookie-cutter offspring that are nearly clones. In other words, there are no longer any hidden recessive genes -- what you see is what you get. From this point on, inbreeding won't really matter much -- except to say that without variation within the population, you'll have to be vigilant about preventing new diseases from getting at your flock. This is why people who begin with an already established line can continue to inbreed without seeing negative effects -- a lot of hard work was already done by the originator of the line to get to that point.

So when someone asks "is it ok to inbreed?" I'd answer "well, what are your goals?" If you want to produce cookie-cutter animals to match the breed's SOP or to produce uniform food, then inbreeding to start a line is probably the way to go. Be prepared, when beginning your own line (not getting animals from another line and continuing it, but starting your own from unrelated individuals) to cull heavily in the first few generations to purge harmful recessives as much as possible. If you keep your animals free-range, be aware that parasites continue to evolve, and with a group of animals with very little variation, it's possible that eventually a disease could decimate the flock. If you want to maintain a population for your own consumption and don't have the resources to raise lots of animals and cull 90% for the first few generations, then a healthy amount of genetic variation would probably suit you better.

P.S. I'm basing my information on some research I've been doing on the origins of inbred lines of mice used in laboratories, and applying those principles to livestock.

 

[flyingmonkeypoop]

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Normally if I kept two trios over I would keep the best young trio and cross the pullets with their father and the hens with a cockerel. When we were working with the polish we did a cross of full siblings after the year of the cyclops chicks and got good birds, just seemed like once we got the worst of the worst we got the best of the best.

 

[punky rooster]

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I could be wrong, but, what I think Saladin is saying is that there are some breeds that CAN be heavily inbred for very long periods of time WITHOUT deleterious effect. Other breeds, not so much, .

That is correct... the production type white leghorn comes to mind(workded witht them)

Ah, I see.

 

[saladin]

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This is not a bad answer at all to the question; except that you narrowed it to exhibition folks. This is not correct. (If you were using them as an example, I wish you would have said so).

The chicken that is bought in the local grocery store is from some of the most highly inbred lines on the planet. Those lines (usually 3; sometimes 4) were then crossed to produce the resulting bird that is eaten.

The eggs bought from the local grocery store are produced by chicks also from 3 or 4 highly inbred lines. (The reason for the lack of taste has nothing to do with the inbreeding).

Cockers the world-over utilize and maintain highly inbred lines of birds.

Thus, whether we are talking commerical, exhibition, or game, the chickens that most affect the world are from highly Inbred Lines of Chickens.

 

[NYREDS]

with a group of animals with very little variation, it's possible that eventually a disease could decimate the flock

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My experience is just the opposite. On those occasions when I have brought in new birds to begin a new project disease is an issue for the first few years. I do not medicate. Period. One of the factors I select for is disease resistance. Once I have established a line I no longer experience any problems with disease. That line of Red Bantams I often mentionas an example. I've bred them for 20 years now & I can't remember the last time one got sick.​

 

[saladin]

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My experience is just the opposite. On those occasions when I have brought in new birds to begin a new project disease is an issue for the first few years. I do not medicate. Period. One of the factors I select for is disease resistance. Once I have established a line I no longer experience any problems with disease. That line of Red Bantams I often mentionas an example. I've bred them for 20 years now & I can't remember the last time one got sick.

I'm in agreement with Red. The only chickens I have on the place that never get sick are the Asil. Asil have been inbred consistently for 3500 years. Several of my lines have been inbred for over 25 years. When a cross is made it has been to another Asil of a similar line.

Breeding for disease resistance is part of the whole Inbreeding scheme (at least it is outside of the commercial world).

 

[MixedBlessings]

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yikes. is this common? is that what people mean when they say to be "prepared to heavily cull"?

Yep. Heavy line-breeding can turn up recessives that are severely detrimental to the children of the pair. The best thing to do is to cull not only the deformed descendants, but the pair that produced them if you can, since they've demonstrated that they both carry the harmful recessives. It takes a lot of test crosses and careful record-keeping to determine which of your first few generations of heavily line-bred animals are clear of recessive traits you want to get rid of.

 

[punky rooster]

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yikes. is this common? is that what people mean when they say to be "prepared to heavily cull"?
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No, I'd say its not "common" in lines that have been managed properly. Heavily inbred lines (I believe there's a difference between that and line-bred), yes, things like this will/can pop up a lot.

When people say "prepared to heavily cull" it can be for different reasons. So, if you want better egg laying, cull the poor egg layers. If you want disease resistance, don't breed birds that get sick. If you want your birds to be up to standard, be prepared to cull, cull, cull to get them there. It's all-the-above for me.

 

[Ridgerunner]

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If you have a mixed flock with different roosters and hens together, you cannot control who mates with whom. It is purely random. Unless they are different purebred colors, you sure can't track it and even then, it is not always possible. After they have crossed and you start breeding crosses to crosses, you lose what little tracking ability you had.

Others have gone into real good detail about how you breed to develop real specific traits, whether it is to breed birds for show, meat, or something else. To me, it is fascinating reading. You select the traits you want and go to great lengths to match specific birds and cull heavily. But what you are talking about is different. It's more like pen breeding, which the hatcheries generally do. That's where you keep several roosters in with several hens and let them mate at random. You still have to carefully select your breeders for the next generation and ruthlessly cull out any birds that don't meet your standards or that show flaws. You are not going to get show quality birds this way, at least not often, but as others have clearly said in this thread, they cull practically all their offspring anyway from specific breedings, not pen breedings.

I don't know of any magic number of roosters and hens you have to have to keep inbreeding problems out of a pen breeding program. I suspect it is a lot like line breeding. It depends on the skills and abilities of the person doing the culling and selecting of breeders.

It gets a little complicated when working out the numbers since you are talking about pairs of genes and the way they pair up, but 'm pretty sure you get the same overall genetic diversity whether you mate a father to daughter, son to mother, or brother to sister. The difference is that if you mate a parent to offspring, you have more control over which traits get reinforced. When you are breeding for specific traits, that is important. If you are just breeding for genetic diversity, which many of us do, it is not as important.