Inbreeding

Inbreeding and line breeding
What are inbreeding and line breeding, and what effect do they have?
In genetic terminology, inbreeding is the breeding of two animals that are related to each other. In its opposite, out crossing, the two parents are totally unrelated. Since all pure breeds of animal trace back to a relatively limited number of foundation dogs, all pure breeding is by this definition inbreeding, although the term is not generally used to refer to matings where a common ancestor does not occur behind sire and dam in a four or five generation pedigree.
Breeders of pure bred livestock have introduced a term, line breeding, to cover the milder forms of inbreeding. Exactly what the difference is between line breeding and inbreeding tends to be defined differently for each species and often for each breed within the species. On this definition, inbreeding at its most restrictive applies to what would be considered unquestioned incest in human beings - parent to offspring or a mating between full siblings. Some people and line breeding call uncle-niece, aunt-nephew, half sibling matings, and first cousin matings inbreeding by others.
What does inbreeding (in the genetic sense) do? Basically, it increases the probability that the two copies of any given gene will be identical and derived from the same ancestor. Technically, the animal is homozygous for that gene. The heterozygous animal has some differences in the two copies of the gene Remember that each animal (or plant, for that matter) has two copies of any given gene (two alleles at each locus, if you want to get technical), one derived from the father and one from the mother. If the father and mother are related, there is a chance that the two genes in the offspring are both identical copies contributed by the common ancestor. This is neither good nor bad in itself. Consider, for instance, the gene for PRA (progressive retinal atrophy), which causes progressive blindness. Carriers have normal vision, but if one is mated to another carrier, one in four of the puppies will have PRA and go blind. Inbreeding will increase both the number of affected dogs (bad) and the number of genetically normal dogs (good) at the expense of carriers. Inbreeding can thus bring these undesirable recessive genes to the surface, where they can be removed from the breeding pool.
Unfortunately, we cannot breed anything based on a single gene - the genes come as a package. We may inbreed and rigorously remove, say pups instance with PRA or even their parents or nest - mates from the breeding stock. However, remember inbreeding tends to make all genes more homozygous. In at least one breed, an effort to remove the PRA-causing gene resulted in the surfacing of a completely different and previously unsuspected health problem. It is easier and faster to lose genes (sometimes very desirable genes) from the breeding pool when inbreeding is practiced than when a more open breeding system is used. In other words, inbreeding will tend to produce more nearly homozygous animals, but generally some of the homozygous pairs will be "good" and others will be "bad.”
Furthermore, there may be genes where heterozygosity is an advantage. There are several variant haemoglobin types in human beings, for instance, where one homozygote suffers from some type of illness, the other homozygote is vulnerable to malaria, and the heterozygote is generally malaria-resistant with little or no negative health impacts from a single copy of the non-standard hemoglobin gene. A more widespread case is the so-called major histocompatibility complex (MHC), a group of genes where heterozygosity seems to improve disease resistance.
Is there a way of measuring inbreeding? Wright developed what is called the inbreeding coefficient. This is related to the probability that both copies of any given gene are derived from the same ancestor. A cold outcross (in dogs, probably a first-generation cross between two purebreds of different, unrelated breeds would be the best approximation) would have an inbreeding coefficient of 0. Note that this dog would not be heterozygous at every locus. There are genes shared with every multicellular organism, genes shared with all animals, genes shared with all animals with backbones, genes shared with all four-limbed animals (including most fish and all amphibians, reptiles, birds and mammals) and with all mammals. Although the DNA might differ slightly, the proteins produced would be functionally the same. Further, the chances are that our dogs with inbreeding coefficient = 0 would still be homozygous for some genes shared by all dogs. The inbreeding coefficient thus specifically refers to those genes that are variable (more than one possible form) in the species and even the breed being considered.
An inbreeding coefficient of 1 (rare in mammals) would result if the only matings practiced over many generations were between full brother and full sister.
The figure shows how the inbreeding coefficient changes with generations of brother-sister matings. As a general rule, this type of mating cannot be kept up beyond 8-10 generations, as by that time the rate of breeding success is very low. However, the rare survivors may go on to found genetically uniform populations. This has been done in laboratory rodents, producing inbred strains of mice and rats so similar genetically that they easily tolerate skin or organ grafts from other animals from the same inbred strain. However, the process of inbreeding used to create these strains generally results in loss of fertility (first seen in these mammals as a reduction in litter size) which actually kills off the majority of the strains between 8 and 12 generations of this extent of inbreeding. A handful of the initial strains survive this bottleneck, and these are the inbred laboratory strains. However, very little selection other than for viability and fertility is possible during this process. You wind up with animals homozygous for a more or less random selection of whatever genes happened to be in the strains that survived, all of which derive from the parents of the initial pair.
Note that two very much-inbred parents can produce offspring that have very low inbreeding coefficients if the inbred parents do not have ancestors in common. This, however, assumes that mates are available who are not strongly inbred on a common ancestor. If the parents are related to each other, their own inbreeding coefficients will indeed increase the inbreeding coefficients of their offspring. The critical factor is the coefficient of kinship, which is the inbreeding coefficient of a hypothetical offspring of the two individuals. Inbreeding has become an important consideration for wildlife conservationists. Many wild populations are in danger of extinction due to some combination of habitat destruction and hunting of the animals, either to protect humans or because the animal parts are considered valuable. (Examples are ivory, rhinoceros horn, and infant apes for the pet trade, as well as meat hunting.) For some of these animals the only real hope of survival is captive breeding programs. However, the number of animals available in such captive breeding programs, especially at a single zoo, is often limited. Biologists are concerned that the resulting inbred populations would not have all of the genes found in the wild populations, and thus lose some flexibility in responding to change. In reaction to this threat, they have developed networks such that animals can be exchanged among captive breeding populations in such a way as to minimize the overall inbreeding of the captive population. The idea is to select pairs in such a way that the inbreeding coefficient of the offspring is kept as low as possible. Most elementary genetics books have instructions for calculating the inbreeding coefficient from the pedigree. (For more information, see Dr. Armstrong's site, Significant Relationships.) However, these procedures have two major limitations. First, they are not really designed for cases where there are multiple common ancestors, though they can be used separately for each common ancestor and the results added. Second, they become impossibly complex as the length of the pedigree increases. It is by no means uncommon in dogs, for instance, to have pedigrees which can be researched in the AKC stud book and the KC Gazette and which go back to foundation dogs born around the turn of the century - perhaps 30 or even 40 generations earlier. With this type of long pedigree, foundation animals may appear a million times or more in the pedigree. With this in mind, a computer program called GENES was developed by Dr. Robert Lacy for the calculation of the inbreeding coefficient, kinship coefficients among animals in the breeding pool, percent contributions of varying founding ancestors, and related output, assuming full pedigrees to the foundation stock were available for all animals currently in the breeding population. For captive breeding populations, the less inbreeding the better, and this is the way the program is used. In pure bred livestock, the situation is a little different - we want homozygosity for those genes, which create a desirable similarity to the breed standard. Wright's defence of inbreeding was based on this fact. However, inbreeding tends to remove those heterozygotes, which are beneficial (e.g., the MHC) as well as increasing undesirable as well as desirable homozygotes. The practice is most dangerous in the potential increase of homozygous health problems which are not obvious on inspection, but which shorten the life span or decrease the quality of life for the animal. I do not at the present time have other dog breeds for comparison, but I recently submitted a Shetland sheepdog pedigree database to Dr. Armstrong for calculation of true inbreeding coefficients. This database was based on full pedigrees of all AKC Shetland Sheepdogs that had sired 10 or more breed champions (males) or produced 5 or more (females.) These top producing animals were set up as the current living population (a somewhat artificial assumption, as the dogs involved where whelped from 1930 to after 1990.) I would love to see some comparisons with other breeds.

Inbreeding, Line breeding and Crossbreeding
from NSAE NEWS VOL. 1 N6- December 12, 1997

INBREEDING's purpose is to fix certain traits or the influence of certain ancestors upon the progeny. This procedure varies in degree from intense close breeding to mild line breeding. Although inbreeding can be detrimental to fertility, vigour, and athletic ability within the offspring, it can also result in true-breeding strains of horses (that consistently pass important traits to their offspring). Because a process of inbreeding formed most breeds, the breeding of purebred horses is, my definition, a form of inbreeding. Some breeds are more inbred than others. (Degree of inbreeding depends on the number of common ancestors, how far back in the pedigree they appear, and how often each common ancestor occurs.)
From a genetic viewpoint, inbreeding results in an increase of the number of homozygous gene pairs in the offspring. Homozygous refers to a condition where two paired chromosomes have the same allelle (gene type) at a corresponding point. Because two close relatives tend to have more of the same alleles (by virtue of inheritance) than two unrelated individuals, their mating provides a greater chance for identical alleles to be paired within their offspring. This increase in homozygosity is directly related to the appearance of both desirable and detrimental characteristics that were not necessarily apparent in the sire and dam.
When horses are inbred haphazardly, without culling of inferior stock, many undesirable traits may become predominant in their offspring. For example, the inbred horse's ability to resist disease and his overall performance capacity are often depressed. The growth rate of the inbred foal, and the average mature size within the inbred herd, frequently decreases. Non - selective inbreeding is directly related to a depressed fertility rate, an increase in abortion and stillbirth. Some basic principles of genetics show why these traits are directly related to inbreeding.
When two unrelated birds are mated, the chances of unidentical alleles combining within the resulting embryo are high. On the other hand, mating close relatives increases the pairing of identical alleles (increases homozygosity). The effect of increased homozygosity is a decrease in the number of heterozygous gene pairs and, subsequently, a decline in heterosis (i.e., loss of vigour and fertility). Although the reason for this allelic interaction is not clear, geneticists believe that its presence contributes to the overall quality of an individual. Therefore, as homozygosity increases within the inbred herd, physical quality controlled by over - dominant alleles declines.
Roland any undesirable genes affecting the bird’s overall vigour and fertility are recessive. Fortunately, they have no influence in the heterozygous state, since the effect of the recessive allele is completely hidden by the effect of the corresponding dominant allele. Because of the overall effect of inbreeding is an increase in homozygosity! it increases the number of homozygous recessives. Hence, the effects of undesirable recessive genes begin to surface. Inbreeding does not create undesirable trait, it exposes recessive alleles for hidden weaknesses, which are present within the sire and dam. Because successful inbreeding demands the culling of inferior breeding stock over many generations (to help eliminate some of the undesirable recessive genes from the herd), it may not be feasible for some breeders. Not only is the time factor impractical for most breeders, the intense culling often necessary may be an economic problem. Additionally, the traits, which tend to surface within the inbred birds (such as depressed growth rate and decreased size, (reminds me of ‘Young Bird Sickness that!) contrast sharply with what many breeders select for. Therefore, the breeder must be objective when the need to cull arises.
Perhaps the greatest advantage of inbreeding is that it increases the pre - potency of individuals within a herd / flock and consequently helps to create distinct true-breeding strains or families. This prepotency (the ability of a stallion or broodmare, for example, to stamp desirable characteristics upon their offspring with a high degree of predictability) is the result of the parent being homozygous for important desirable traits. When such a parent carries two identical alleles on corresponding points of a chromosome pair, he transmits that allele to the same chromosome point within his offspring. If two such parents are mated, the offspring will always possess the same desirable trait. Therefore, as inbreeding increases homozygosity, it also enhances prepotency. (This is advantageous only if the parents are homozygous for desirable traits.)
As mentioned previously, inbreeding exposes certain weaknesses within the inbred herd. Uncovering these undesirable traits can be an important tool for the overall improvement within a large breeding program. By setting certain selection guidelines, and by carefully eliminating inbred individuals which show inherits weaknesses, the breeder can slowly remove any undesirable recessive genes from their herd. They will find that vigour and fertility are actually improved when inbreeding is accompanied by careful selection.
A successful inbreeding program requires good foundation stock and severe culling over many years. For this reason, experienced breeders who operate large farms for the production of superior proponent breeding stock usually practice inbreeding. It can also be used to establish breeds, or true-breeding types, with respect to certain characteristics such as colour or size.
A breeding system, which uses extreme inbreeding, such as mating between siblings or between parents and offspring, is referred to as CLOSE BREEDING. The detrimental effects of inbreeding (such as decrease in vigour, fertility, athletic ability and size) are usually exaggerated in a close breeding system. This is especially true when average breeding stock is used and little culling has been implemented. Close breeding can produce extremely good, or extremely poor, results. Success and failure depend on factors such as planning, foundation stock, emphasis on culling, and completeness of pedigree and performance records, etc. Haphazard close breeding could be very detrimental to the overall quality of the resulting offspring. To avoid disaster, a careful study of the merits and weaknesses of the breeding stock should precede a close breeding program. Only the most outstanding mares and stallions can be used with any degree of safety in a long-term close breeding program.
Close breeding is a valuable tool in genetic research, since it quickly exposes hidden gene types that an individual carries. Because of its extreme nature and the chance, that it may suddenly cause undesirable effects in the offspring. Horse breeders do not often use close breeding. Some breeders, who operate large and well-organized program, might utilize close breeding if they progeny test their stallions. (One method of progeny testing a sire is to mate him to a large group of his own daughters. A study of the offspring determines whether he carries undesirable genes hidden in the heterozygous state.) After a stallion proves that he is of superior gene type, the experienced breeder may choose to continue the close breeding to increase prepotency of future breeding stock.
LINE BREEDING, the most conservative form of inbreeding, is usually associated with slower improvement and limited risk of producing undesirable individuals. It can involve matings between closely or distantly related horses, but it does not emphasize continuous sire-daughter, dam-son, or brother-sister matings. The main purpose of line breeding is to transmit a large percentage of one outstanding ancestor's genes from generation to generation without causing an increase in the frequency of undesirable traits often associated with inbreeding.
Because line breeding is not based strictly on mating closely related individuals (with very similar gene types), it does not necessarily cause a rapid increase in homozygous gene pairs. Consequently, it will not expose undesirable recessive genes as extensively as close breeding. For this reason, line breeding is generally a safer inbreeding program for most breeders.
Intensive inbreeding (and resulting increased homozygosity) is often directly related to an increase in the expression of many undesirable traits. Therefore, the line breeder should carefully study pedigrees for each prospective mating and determine if, and how closely, the mare and stallion are related. By following certain guidelines, the breeder can limit inbreeding (and, therefore, homozygosity) within their herd. At the same time, they may increase the influence of a common ancestor upon the entire strain or family.
CROSSBREEDING is the mating of horses from different breeds. Cross breeding may also be used to produce heterosis, the sudden increase in vigour and fertility caused by a sudden increase in heterozygosity. Because horses from separate breeds usually carry very different genotypes, crossbreeding causes an extreme form of heterosis. The possibility of each parent contributing identical alleles to their offspring is remote. Heterosis from crossbreeding often appears as a sudden improvement in physical characteristics, such as size, endurance, disease resistance, etc. New breeds are sometimes established by crossing members of two or more breeds and carefully inbreeding the original crossbred offspring. Crossbreeding initiates the desired change, while inbreeding increases the ability of each generation to breed "true to type.”
Author Anonymous
NSAE NEWS
National School of Academic Equitation
22131 31st Avenue SE
Bothell, WA 98021
(425) 806-8171
Craig P. Stevens
Director
cpszzz@concentric.net
Copyright 1997 - Craig P. Stevens, Director, National School of Academic Equitation.
Printed here by special permission.

So true!

Very good Daz, but could have been put in far fewer paragraphs and most just common sense.

Had the creator not involved mankind then there would have been no problems.

Giving mankind the freedom of choice and all that the earth involves ?????.

Regards.

Very True Misty …
Man tampers and destroys constantly. Indeed one would be hard pressed, very hard pressed indeed to find any thing that he has improved.... Well there isn't one thing. yes seems so often in the short term, then truth comes out.

Sometimes, and not always wisely lol.

However I see many times now the wails and moans of 'Losses', and the reasons put forward. B.O.P. for instance. Yes, they can and would split the flock and cause great distress etc. But the answer is not that solely. NOT by a long chalk. Weather, today, Conveyers, race Controllers etc. etc and the list goes on, are all reasons raised up, plus many more even dafter and nonsensible.
A realism of fact is that in the 50's / 60's 150.000 fanciers sent far, far fewer than today's' 25,000 fanciers do!
Big teams was a luxury most couldn't afford. indeed, by and large, most never even bothered to dream about! Training! What training, the 3/6 (!7p) was a worry when a stray was reported. The 2/- - 2/6 fare on the train for training was an expense many couldn't afford or did. Indeed it was essentially proven to be not needed. The Frankie George, Masserella's etc. did have good wins, no two ways about that. But were beaten so very often by club members!

You know, I wanted and tried to get, 3 or four strays that had dropped into others lofts. Liked the thought of Reds and Grizzles, especially a red Grizzle, or red mealies. Let them choose a mate and race the youngsters. I was, and am still, confident that they would more than hold their own.

I think now, as then, that if two fanciers were to swap 6 pairs or 12 cocks/hens and kept them separately and mated to their own Cocks/hens, and built a team from them. Made sure the offspring were related when breeding from THEN losses would soon be controlled and lessened by far In all lofts that did it.
JUST like the good fanciers do year in and year out. They don't buy in too many! They swap with other good flyers! Ok a few buy big from Masserella and mix them in each year!

just liberated a stray this morning about 8.00am, took it 3 miles away, made sure it had food and water before we went........no sign of it since, hopefully it has managed to find its way home with ets ring in tact.

45 pound isn't cheap now to get them returned, maybe why so many don't want them back........I remember when it was £7.50 and it went back on the train, things rarely alter for the better

Daz,

There are several reasons for the loss of many of the pigeons of today.

Main one too many are bred that are not capable of doing what the fancier wants them to do and in asking them to do it loses them, relative to the basic capabilities that they are born with.

Then you have pigeons with the potential to do well but are ruined by bad management.


Bad transportation and the lack of ensuring that the pigeons on release are in as good a condition as when put on the transporter.


Losses when doing unnecessary training up and down which gives preditors a good meal on a plate, the more more times the raptors have to damage the pigeons ????.

Just a few examples, but the main reason the pigeons of today are propped up by artificial means to such an extent that they are nothing more than robots.


Regads.

I think you describe me misty, my birds won well for the previous owner, and also ybs I have bred for others have flown well..............bad management from me this year, hope to learn from mistakes.

Took a youngster to Wales - was going that way. Let it up about 7 miles from its loft. Weather looked ominous and time was pressing. No sooner had it been released the heavens opened up.
Poured down all the way home 200 miles odd... It was on the loft in the morning !

you cant understand it sometimes daz, took strays miles away from my loft, they come back.......take my own a mile down the road they never come back

A stray came into the loft and had a name address ring on, contacted the fancier and he lived in London, this in the last year I kept my pigeons a few years ago, the pigeon was in good condition, I contacted the fancier straight away, he said he had had a bad time and had to send for several pigeons after a disaster.

I have a friend whose son was a police officer in London, now transfered to Yorkshire who was to visit that week end and said I would get him to take it and release it in London.

He took the pgeon and released it in London at 2.00 pm, my said I bet it comes back, looked in the loft at 6pm and the pigeon was back, gave the fancier a ring and said I would send it back and pay the costs.


He said thanks but you can keep it if you wish and gave me the breeding as a
Mark Evans bird bred from the best, and by handling etc; it was a good bird, I did not have time to breed from it as it was too close to when I had to let the pigeons go.

So I kept it and it went with all my other pigeons when I had to part with them through pigeon lung etc;

A young one, just about out of squaking still with plenty of down on, escaped from the pannier when the fanciers I gave the pigeons to were taking them out of the pannier, it was back in my loft from 70 miles the next morning.

A pigeon bred from pigeons that have had open loft in the same location over many years have and retain a better homing instinct to the area concerned, than choppig and changing.

For every story in the sport there will be others that appear to contradict what is generally accepted as normal, if we new it all where would the enjoyment be????




Regards.

MISTY wrote:

A stray came into the loft and had a name address ring on, contacted the fancier and he lived in London, this in the last year I kept my pigeons a few years ago,  the pigeon was in good condition, I contacted the fancier straight away, he said he had had a bad time and had to send for several pigeons after a disaster.

I have a friend whose son was a police officer in London, now transfered to Yorkshire who was to visit that week end and said I would get him to take it and release it in London.

He took the pgeon and released it in London at 2.00 pm, my  said I bet it comes back, looked in the loft at 6pm and the pigeon was back, gave the fancier a ring and said I would send it back and pay the costs.


He said thanks but you can keep it if you wish and gave me the breeding as a
Mark Evans bird bred from the best, and by handling etc; it was a good bird, I did not have time to breed from it as it was too close to when I had to let the pigeons go.

So I kept it and it went with all my other pigeons when I had to part with them through pigeon lung etc;

A young one, just about out of squaking still with plenty of down on, escaped from the pannier when the fanciers I gave the pigeons to were taking them out of the pannier, it was back in my loft from 70 miles the next morning.

A pigeon bred from pigeons that have had open loft in the same location over many years have and retain a better homing instinct to the area concerned, than choppig and changing.

For every story in the sport there will be others that appear to contradict what is generally accepted as normal, if we new it all where would the enjoyment be????




Regards.  


 

interesting read misty....whats members thoughts on a first cross from 2 relatively closely bred families

I read in the B.H.W. 1985 / 86 I believe. Been told it was Germany... but thought it was Sweden. Any way a fancier in Oxford went to the loft there. bought and Brought some back. One in the nest was about to leave the nest. Never out the box proper, let alone the loft.
He took them home and kept them in for future stock … which was of course why he bought them.
2 years later one got out and disappeared. It had gone back to where it was born. They were deciding whether to send back, or let it stay. 3 days later it was back in Oxford. Later it was raced and actually won.

Providing both families are of winning blood lines there is no reason why each should not invigorate any offspring, and not having been artificially treated all their lives.

Some of the best pigeons have been from the results of first crosses of inbred families.

The fact is that if you breed enough from any established family of pigeons you will breed a large number of rubbish and a very few realy good ones.

That also applies in every other circumstance.


Regards.

thanks misty its my intention to breed this way next year

True Misty. Incest for blood / genes... Once. Outcross for racing.
Too many, at great cost to themselves and our sport have no idea why and how, and as such fill their lofts with culls. then make 1000's of excuse … any thing and everyone barr themselves... Sadly.