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Line-breeding and in-breeding thoughts & reasons

This is a discussion on Line-breeding and in-breeding thoughts & reasons within the Horse Breeding forums, part of the Horse Breeds, Breeding, and Genetics category

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        09-20-2013, 12:33 PM
      #41
    Super Moderator
    Quote:
    Originally Posted by dbarabians    
    The 2 yo Babson bred colt I is cow hocked. Pretty badly I might add. I bought his mother when she was in foal with him. She has very good legs. She had been turned out with a stallion and already produced a colt with him. He too was cowhocked.
    Researching the stallion I discovered he and a few other foals he sired are cow hocked. Not as bad as my colt.
    If I ever bred her to another Babson bred stallion to keep the line going in my herd I would find one like Lady my mare with straight correct legs.
    This years colt she had is very very correct. The outcross to my stallion was very successful. They are distantly related 4 generations back.
    I believe firmly in breeding related horses. My family has done so with cattle for generations with great results.
    Yet I follow the rule my family has. I might breed father to daughter or grand father to Grand daughter but I would never breed those offspring back to their father.
    Star has sired 5 fillies with my mare Dancer his half sibling. All have been correct and very nice horses. I would never breed one of those fillies back to their sire or a half sibling.
    The fault has to be present genetically to be passed on so as Chillaa explained inbreeding does not cause defects. Shalom
    ok,. I am just jumping in here with NO breeding experience at all, but I wonder about this statement.

    many recessive traits are present genetically but not expressed in the physical animal becuase they are recessive, right?. Would they not be more likely to be expressed in the offspring if the mother was bred to a related sire, who also had the same recessive genetic traits? There would be no dominant gene to prevent expression of that recessive gene.
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        09-20-2013, 12:39 PM
      #42
    Green Broke
    Quote:
    Originally Posted by busysmurf    
    Another thought. By in-breeding, and essentially limiting the gene pool, aren't you eliminating the possibility of introducing more desired traits? Such as immunity, stronger legs, etc.?

    So in essence, by limiting the gene pool aren't you contributing to the downslide of a breed by preventing sustainable diversity?
    Not if done correctly. The Bedouins created a pure, strong breed that has been utilized by various breeders of various breeds over thousands of years. If this would have caused a down-slide, I think we would have seen it by now.
    Arabians have been used to improve most other breeds in existence. If they were actually lacking, this would never have been done. I don't see other breeds being introduced to Arabians to improve them.

    Again the key to what they created was ruthless culling and great care with choosing individuals.
    dbarabians and HorseLovinLady like this.
         
        09-20-2013, 12:42 PM
      #43
    Yearling
    Inbreeding, Linebreeding and Crossbreeding
    INBREEDING's purpose is to fix certain traits or the influence of certain ancestors upon the progeny. This procedure varies in degree from intense closebreeding to mild linebreeding. Although inbreeding can be detrimental to fertility, vigor, and athletic ability within the offspring, GRANTED: it can also result in true-breeding strains of horses (that consistently pass important traits to their offspring). Because most breeds were formed by a process of inbreeding, 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. Nonselective 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 horses 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 vigor 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 overdominant alleles declines.
    Many undesirable genes affecting the horse's overall vigor 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 herd (such as depressed growth rate and decreased size) 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 prepotency of individuals within a herd and consequently helps to create distinct true-breeding strains or families. This prepotency (the ability of a stallion or broodmare 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 inherit weaknesses, the breeder can slowly remove any undesirable recessive genes from their herd. They will find that vigor 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, inbreeding is usually practiced by experienced breeders who operate large farms for the production of superior prepotent breeding stock. It can also be used to establish breeds, or true-breeding types, with respect to certain characteristics such as color or size.

    From the same source you quoted Druydess
         
        09-20-2013, 12:43 PM
      #44
    Green Broke
    Quote:
    Originally Posted by tinyliny    
    ok,. I am just jumping in here with NO breeding experience at all, but I wonder about this statement.

    many recessive traits are present genetically but not expressed in the physical animal becuase they are recessive, right?. Would they not be more likely to be expressed in the offspring if the mother was bred to a related sire, who also had the same recessive genetic traits? There would be no dominant gene to prevent expression of that recessive gene.
    That would be a 50/50 chance of expression. And there's no guarantee that an outcross wouldn't carry the same recessive gene. The numbers and odds are what needs to be weighed when considering pairs to be mated. Many people breed unrelated horses who have recessive genes unbeknownst to them. By doing one's homework and knowing what a horse carries, you have better odds at limiting defects, even in closely related horses - probably more-so as a breeder has much more incentive to test and study the lines of close pairings.
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        09-20-2013, 12:45 PM
      #45
    Green Broke
    The most important line qualifying the concept, busy: When horses are inbred haphazardly, without culling of inferior stock, many undesirable traits may become predominant in their offspring.

    And- 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 inherit weaknesses, the breeder can slowly remove any undesirable recessive genes from their herd. They will find that vigor and fertility are actually improved when inbreeding is accompanied by careful selection.
    dbarabians likes this.
         
        09-20-2013, 12:51 PM
      #46
    Super Moderator
    That is true.
    dbarabians likes this.
         
        09-20-2013, 12:53 PM
      #47
    Yearling
    "A successful inbreeding program requires good foundation stock and severe culling over many years. For this reason, inbreeding is usually practiced by experienced breeders who operate large farms for the production of superior prepotent breeding stock."

    So what are you willing to kill off any of your inbred foals to achieve the "superior" foal?

    Because, honestly, I haven't met a single person here who I believe would be willing to do that, not that I blame them. But, as ALL of the articles have stated time & time again only successful and responsible breeders that chose to inbreed are willing to kill an undesirable foal. Otherwise, they are continuing the undesirable traits.
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        09-20-2013, 12:59 PM
      #48
    Green Broke
    Well-- I don't know how we get to killing foals from a breeding debate...
    Seems a bit extreme.. perhaps a good 4-H home might be a better solution.. LOL

    BTW-- the Bedouins didn't kill all their foals; they sold many of their unwanted get, especially stallions. Those very "outcrosses" re-introduced defects.
         
        09-20-2013, 01:10 PM
      #49
    Yearling
    Quote:
    Originally Posted by Druydess    
    Well-- I don't know how we get to killing foals from a breeding debate...
    Seems a bit extreme.. perhaps a good 4-H home might be a better solution.. LOL
    It comes from the inbreeding - line-breeding debate. You yourself said that by inbreeding produces superior foals. Correct? But to get to those SUPERIOR foals, the breeder MUST cull / kill the INFERIOR foals. You keep skipping over that part of the equation and it's an integral part of the debate. A necessary evil if you will. You CANNOT validate inbreeding, unless you are willing to eliminate the inferior product. As crappy as that is.

    And by allowing "inferior" horses to go to "a good 4-H" home, isn't that a little irresponsible? Unless as a breeder you are going to spay & neuter every inferior offspring you produce and are completely ok, with having your name on a less than stellar example of what you produce out there? Because to a kid, having a horse with papers = bragging rights. While the kids may not understand the implications, parents who understand will associate that breeder with sub-par quality. I know I would, as well as most others I know.

    As a "4-H home", I don't want an Ooops horse for my daughter, I want a sound & healthy example of whatever breed we choose, be it a "purebred" or a "cross breed".
         
        09-20-2013, 01:14 PM
      #50
    Green Broke
    No-- it really isn't. All beings have a purpose. Many horses are healthy and able to perform just fine without being breeding perfection. Jumping to extreme conclusions isn't helpful in a debate.
         

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