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<blockquote data-quote="simme" data-source="post: 1647678" data-attributes="member: 40418"><p>This is a simplified explanation. But it is still somewhat complicated. WW EPD calculations are not based on the actual numerical weaning weight. They are based (and change) based on the differences in weaning weight of the calves in a contemporary group based on who the sire is. If there were 50 calves in a contemporary group (means they were born and raised on the same farm in the same pastures and all treated the same - environment and feed are the same for all) and the 50 calves were sired by 5 different bulls (for simplicity, lets say that all 50 cows were full sisters - genetically equal). This farm has ideal conditions and feeds the cows and calves well. The five sire groups wean at 700, 725, 750, 775, and 800 pounds on average. This would indicate that the first sire ww EPD should be 25 pounds less than sire 2 and 100 pounds less than sire 5. Another farm has 50 full sisters bred to the same 5 bulls. Environmental conditions here are tough. No extra feed, bad weather, etc. The weaning weights here are 500, 525, 550, 575 and 600. Again sire 1 WW EPD effect would indicate that calves would wean 25 pounds less than sire 2. Essentially the same DIFFERENCES as seen for the same 5 sires at the other farm where nutrition is much higher. Numbers are way different between the two farms, but calculation of genetic potential are the same. EPD's only change based on actual submitted data within a contemporary group - not sire 2 calves weaning at a higher weight on farm 1 that sire 1 calves weight on farm 2. Adjustments are only made based on differences between sire groups on the same farm in the same pasture treated the same.</p><p></p><p>If all 50 calves weaned at the same weight (say 900 pounds on one farm and 400 pounds on another farm), EPD's would indicate equal WW EPD for all five bulls based on the difference, not actual weights. EPD's are not adjusted by comparing performance on one farm vs another farm. Too many other variables that can't be accounted for.</p><p></p><p>So, if you have a calf with a 900 pound weaning weight and your friend a couple states over have calves by a different sire that wean at 800 pounds, you can't make any conclusion about EPD's from that. EPD calculations and changes require comparison of actual weights from calves in the same contemporary group with multiple sires represented. More data from more calves from more sire groups in the same contemporary group is what drives EPD's and accuracy.</p><p></p><p>That is the simplified version. In actual practice, the cows are not all full sisters. So there are calculations taking into account the data from all the animals in the pedigrees - bits and pieces of statistical data from all the contemporary groups reported. Then there are calculations based on antagonistic traits. For instances, high growth in a calf will result in a DECREASE in the dam's milk EPD. I have always thought that high weaning weight would be an indication that the dam was a good milker. I can't rationalize how high weaning weight causes the dam's mild EPD to decrease, but am told that is the case. Maybe someone can explain that.</p><p></p><p>I am no expert. If anyone has better or more info, please share. The above is my understanding.</p></blockquote><p></p>
[QUOTE="simme, post: 1647678, member: 40418"] This is a simplified explanation. But it is still somewhat complicated. WW EPD calculations are not based on the actual numerical weaning weight. They are based (and change) based on the differences in weaning weight of the calves in a contemporary group based on who the sire is. If there were 50 calves in a contemporary group (means they were born and raised on the same farm in the same pastures and all treated the same - environment and feed are the same for all) and the 50 calves were sired by 5 different bulls (for simplicity, lets say that all 50 cows were full sisters - genetically equal). This farm has ideal conditions and feeds the cows and calves well. The five sire groups wean at 700, 725, 750, 775, and 800 pounds on average. This would indicate that the first sire ww EPD should be 25 pounds less than sire 2 and 100 pounds less than sire 5. Another farm has 50 full sisters bred to the same 5 bulls. Environmental conditions here are tough. No extra feed, bad weather, etc. The weaning weights here are 500, 525, 550, 575 and 600. Again sire 1 WW EPD effect would indicate that calves would wean 25 pounds less than sire 2. Essentially the same DIFFERENCES as seen for the same 5 sires at the other farm where nutrition is much higher. Numbers are way different between the two farms, but calculation of genetic potential are the same. EPD's only change based on actual submitted data within a contemporary group - not sire 2 calves weaning at a higher weight on farm 1 that sire 1 calves weight on farm 2. Adjustments are only made based on differences between sire groups on the same farm in the same pasture treated the same. If all 50 calves weaned at the same weight (say 900 pounds on one farm and 400 pounds on another farm), EPD's would indicate equal WW EPD for all five bulls based on the difference, not actual weights. EPD's are not adjusted by comparing performance on one farm vs another farm. Too many other variables that can't be accounted for. So, if you have a calf with a 900 pound weaning weight and your friend a couple states over have calves by a different sire that wean at 800 pounds, you can't make any conclusion about EPD's from that. EPD calculations and changes require comparison of actual weights from calves in the same contemporary group with multiple sires represented. More data from more calves from more sire groups in the same contemporary group is what drives EPD's and accuracy. That is the simplified version. In actual practice, the cows are not all full sisters. So there are calculations taking into account the data from all the animals in the pedigrees - bits and pieces of statistical data from all the contemporary groups reported. Then there are calculations based on antagonistic traits. For instances, high growth in a calf will result in a DECREASE in the dam's milk EPD. I have always thought that high weaning weight would be an indication that the dam was a good milker. I can't rationalize how high weaning weight causes the dam's mild EPD to decrease, but am told that is the case. Maybe someone can explain that. I am no expert. If anyone has better or more info, please share. The above is my understanding. [/QUOTE]
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