Just so I am clear, what are you considering hallmarks? I was assuming you were meaning type in general, the things that make a bird a particular breed.
Yes, that's correct.
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Breeds seem to have been created for a few reasons. Some combined birds with traits they liked, both productive and aesthetic, and refined what they got out of those crosses. If one wanted egg production, Leghorn or Minorca was used. If one wanted size, Asiatics such as Cochins were used.
Yes, the Light Sussex was made from the Silver Grey Dorking, Cochin, Brahma .
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If you want production, you select for those characteristics. If the aesthetics are not selected for, the type changes quickly.
Ok now I know why Aesthetics are important.
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I come from a broad poultry background. I look at all sides. My son and I show birds, although it is mainly my son, as I let him choose the birds he wants to show, and I might take a few if I think they should be shown. With that said, I am breeding towards the standard of perfection, as that is what they are judged on.
Ok that's the road I am traveling too.
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If I wanted a productive bird, I would not care about tail angles, angle of back, lacing, etc.
Why can't we have both?
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Unfortunately, many exhibition breeders did not put any selection pressure on production, and many birds only look the part now.
Yes, it's the old fancy vs utility thang. C. J. Davies explained it so well in his " The Theory And Practice Of Breeding To Type".
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If breeding to the standard meant breeding for production, some show lines would be much more productive.