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EPDs (again.....) those who follow and those who don't
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<blockquote data-quote="simme" data-source="post: 1716182" data-attributes="member: 40418"><p>On the subject of EPD's, management, and visual observation: Visual observation (phenotype), firsthand knowledge of the cow family and discussions with other producers are important information for sure. Look just at one trait - weaning weight. Easily measured in pounds. Say you visit with a producer with a large number of calves sired by 2 different bulls. In that herd, the steer calves sired by bull A have an average 205 day adjusted weaning weight of 660 pounds. The steer calves sired by bull B have an average weaning weight of 700 pounds. Both sets of calves look good and the owner is pleased with both groups. Dams look good as well. What would you decide from the observations? Both bulls are good? Bull B is the bull to use? Bull A calves have good growth or bad growth? Both 660 pounds and 700 pounds seem like good weights.</p><p></p><p>Then you visit another producer that you trust. He has a large number of calves sired by two different bulls. Average 205 adjusted weaning weight on bull C steer calves is 510 pounds. Average for bull D steer calves is 550 pounds. Dams of the calves look good, but are thinner than the other producer's cows. Owner is pleased with the calves. What observations would you make from this visit? Neither bull C or D is the bull to use since the weaning weights are less than you want? Bull D is the bull to use? The first producer selected better bulls than the second producer? Having thin cows is not good? Bull B must sire more weaning weight potential than Bull A? Bull C and D must not sire much weaning weight potential?</p><p></p><p>Then you notice that both producers used the same two bulls. Bull A is the same bull as C. Bull B is the same bull as D. Point being is that weaning weight EPD's are <strong>not </strong>calculated on actual weaning weights reported. They are calculated based on <strong>differences </strong>in actual adjusted weaning weights of different sire groups <strong>within </strong>the <strong>same </strong>herd and <strong>same </strong>pasture and <strong>same </strong>conditions. First producer turns in his weaning weights and the EPD machine calculates that bull B sires calves on average 40 pounds heavier at weaning than bull A. 700- 660 = 40.</p><p>Second producer turns in his weaning weights and the EPD machine calculates that bull D sires calves on average 40 pounds heavier than bull C. 550 - 510 = 40. My examples are basic and simplistic.</p><p></p><p>Weaning weight EPD's are just calculated differences in actual weaning weights for many calves measured over many sire groups in many herds. Herd 1 weights are never compared to herd 2 weights for EPD calculations. If that were the case, EPD's would be meaningless. Contributions to EPD updates are only based on different sire groups in the same herd under the same condition. Then those within herd differences are averaged together over all herds in the database to calculate new EPD's. Not a perfect system, but seems to me that there is some good data there. Maybe as good or better than the physical observation example above.</p><p></p><p>Short comings of weaning weight EPD. Say that producer 1 above owns bull B and sells semen on the bull as well as sons in his production sale. He could put the toe of his boot on the scale when a calf sired by bull B comes over the scale. He could manipulate the weaning weight EPD for bull B if he has a large number of them compared to bull B calves in other herds. Point is that there is a way to cheat if you own most of the calves sired by the bull. If/when the bull is used in more herds, the ability to manipulate is less unless there is a conspiracy with all your buddies. Having incorrect sires listed (on purpose or by accident) will contribute to inaccurate EPD's. I have read that around 10% of registered cattle do not blood type to their listed sire, best I remember that was the number.</p><p></p><p>Point is that management and feed differences between farms do not affect EPD calculations. I don't think there is a conspiracy at the breed association to manipulate EPD's for the benefit of certain members or directors. I still think that EPD's are a good tool for selection along with all the other tools and information.</p></blockquote><p></p>
[QUOTE="simme, post: 1716182, member: 40418"] On the subject of EPD's, management, and visual observation: Visual observation (phenotype), firsthand knowledge of the cow family and discussions with other producers are important information for sure. Look just at one trait - weaning weight. Easily measured in pounds. Say you visit with a producer with a large number of calves sired by 2 different bulls. In that herd, the steer calves sired by bull A have an average 205 day adjusted weaning weight of 660 pounds. The steer calves sired by bull B have an average weaning weight of 700 pounds. Both sets of calves look good and the owner is pleased with both groups. Dams look good as well. What would you decide from the observations? Both bulls are good? Bull B is the bull to use? Bull A calves have good growth or bad growth? Both 660 pounds and 700 pounds seem like good weights. Then you visit another producer that you trust. He has a large number of calves sired by two different bulls. Average 205 adjusted weaning weight on bull C steer calves is 510 pounds. Average for bull D steer calves is 550 pounds. Dams of the calves look good, but are thinner than the other producer's cows. Owner is pleased with the calves. What observations would you make from this visit? Neither bull C or D is the bull to use since the weaning weights are less than you want? Bull D is the bull to use? The first producer selected better bulls than the second producer? Having thin cows is not good? Bull B must sire more weaning weight potential than Bull A? Bull C and D must not sire much weaning weight potential? Then you notice that both producers used the same two bulls. Bull A is the same bull as C. Bull B is the same bull as D. Point being is that weaning weight EPD's are [B]not [/B]calculated on actual weaning weights reported. They are calculated based on [B]differences [/B]in actual adjusted weaning weights of different sire groups [B]within [/B]the [B]same [/B]herd and [B]same [/B]pasture and [B]same [/B]conditions. First producer turns in his weaning weights and the EPD machine calculates that bull B sires calves on average 40 pounds heavier at weaning than bull A. 700- 660 = 40. Second producer turns in his weaning weights and the EPD machine calculates that bull D sires calves on average 40 pounds heavier than bull C. 550 - 510 = 40. My examples are basic and simplistic. Weaning weight EPD's are just calculated differences in actual weaning weights for many calves measured over many sire groups in many herds. Herd 1 weights are never compared to herd 2 weights for EPD calculations. If that were the case, EPD's would be meaningless. Contributions to EPD updates are only based on different sire groups in the same herd under the same condition. Then those within herd differences are averaged together over all herds in the database to calculate new EPD's. Not a perfect system, but seems to me that there is some good data there. Maybe as good or better than the physical observation example above. Short comings of weaning weight EPD. Say that producer 1 above owns bull B and sells semen on the bull as well as sons in his production sale. He could put the toe of his boot on the scale when a calf sired by bull B comes over the scale. He could manipulate the weaning weight EPD for bull B if he has a large number of them compared to bull B calves in other herds. Point is that there is a way to cheat if you own most of the calves sired by the bull. If/when the bull is used in more herds, the ability to manipulate is less unless there is a conspiracy with all your buddies. Having incorrect sires listed (on purpose or by accident) will contribute to inaccurate EPD's. I have read that around 10% of registered cattle do not blood type to their listed sire, best I remember that was the number. Point is that management and feed differences between farms do not affect EPD calculations. I don't think there is a conspiracy at the breed association to manipulate EPD's for the benefit of certain members or directors. I still think that EPD's are a good tool for selection along with all the other tools and information. [/QUOTE]
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