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<blockquote data-quote="jhambley" data-source="post: 616219" data-attributes="member: 1535"><p>I'm not arguing that everyone should use "old style" genetics. I would argue that the Hereford breed is far more genetically diverse today than it was even 60 years ago.</p><p></p><p>I would also argue that you'll never produce a herd capable of consistently reproducing itself using outcrossed genetics. It's not anymore likely than outcrossing to another breed. After all, inbreeding/linebreeding small populations, while applying consistent selection pressure, is how the breeds were first established. </p><p></p><p>Progress toward a homozygous state will never be achieved by outcrossing. Even if you purchase a line bred bull, as soon as you breed him to your unrelated cows, you take a drastic step backwards in achieving a homozygous state. You then have to start over again breeding the resulting animals to your linebred population. The whole promise of linebreeding is that it brings recessive traits into a more homozygous condition. If the trait is beneficial you keep it, if the trait is unwanted or lethal, it's culled. </p><p></p><p>Jim Lents says: "Linebreeding doesn't create new genes. It simply concentrates all genes with equal pressure. When line breeding, the traits you select for, and more importantly, the ones you do not specifically select against, come forward in greater concentration." </p><p></p><p>You can look to race horsing to see Mr. Lents wisdom in action:</p><p></p><p></p><p></p><p>I'm not trying to start a war here but you have to wonder how many generations of linebreeding it would have taken to discover curly calf syndrome? A clean gene pool was the primary reason the Gudgell & Simpson genetics were used to rebuild the Hereford breed after dwarfism was discovered. Through linebreeding, the lethal genetics were most likely identified and discarded.</p><p></p><p>Franklin Nash, when asked about genetic dependability was quoted as saying:</p><p>"Through generations in our herd, we have only tied to a sire after we know what he is (after we have bred him to 20 of his half sisters or 10 of his daughters)." How many producers of AI sires would be willing to do that today?</p></blockquote><p></p>
[QUOTE="jhambley, post: 616219, member: 1535"] I'm not arguing that everyone should use "old style" genetics. I would argue that the Hereford breed is far more genetically diverse today than it was even 60 years ago. I would also argue that you'll never produce a herd capable of consistently reproducing itself using outcrossed genetics. It's not anymore likely than outcrossing to another breed. After all, inbreeding/linebreeding small populations, while applying consistent selection pressure, is how the breeds were first established. Progress toward a homozygous state will never be achieved by outcrossing. Even if you purchase a line bred bull, as soon as you breed him to your unrelated cows, you take a drastic step backwards in achieving a homozygous state. You then have to start over again breeding the resulting animals to your linebred population. The whole promise of linebreeding is that it brings recessive traits into a more homozygous condition. If the trait is beneficial you keep it, if the trait is unwanted or lethal, it's culled. Jim Lents says: "Linebreeding doesn't create new genes. It simply concentrates all genes with equal pressure. When line breeding, the traits you select for, and more importantly, the ones you do not specifically select against, come forward in greater concentration." You can look to race horsing to see Mr. Lents wisdom in action: I'm not trying to start a war here but you have to wonder how many generations of linebreeding it would have taken to discover curly calf syndrome? A clean gene pool was the primary reason the Gudgell & Simpson genetics were used to rebuild the Hereford breed after dwarfism was discovered. Through linebreeding, the lethal genetics were most likely identified and discarded. Franklin Nash, when asked about genetic dependability was quoted as saying: "Through generations in our herd, we have only tied to a sire after we know what he is (after we have bred him to 20 of his half sisters or 10 of his daughters)." How many producers of AI sires would be willing to do that today? [/QUOTE]
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