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EPD question
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<blockquote data-quote="simme" data-source="post: 1658398" data-attributes="member: 40418"><p>Keep in mind that the calculation of EPD's is very complex. The explanation that I offered above is a very simplistic rough view because that is about as far as my understanding goes when you get into the deep details. Mathematical/statistical models are very complex. With EPD's, there are some traits that are inter-related to other traits. The models must take the physical measured and observed data and correctly/best assign it to an EPD trait. For instance, weaning weight is easily measured. But what portion is due to the milk quantity and milk quality of the dam and what portion is due to the growth ability of the animal? How much growth came from the dam and how much from the sire? The complex mathematical models attempt to resolve all that. The weaning weights on your five bulls all being inputs to the model resulting in updated EPD's not only to your 5 bulls, but to all the contributing animals in their pedigree back for generations. I expect that for these complex relationships the models have to be run thousands of times until the numbers all finally converge. Each run using intermediate results from the previous run until the final numbers remain the same. When EPD's were developed many years ago, the computing ability and cost dictated that the EPD's were only updated once or twice a year - due to effort and cost. I think now they can be updated daily.</p><p></p><p>Some people don't put any value in EPD's and some perhaps put too much faith in them. But, I believe they should be one of the tools used. Most any cow/calf person with at least a few cows can name/identify their best or better cows. They know which cows wean the heavier calves year after year. Which cows have higher BW calves and which cows have lower birth weight calves. Which milk better than the others. All based on observation and measurement. If you sell your calves at the auction barn, you can read the weights on the statement. That in a simple nutshell is the principle behind EPD's. Predicting the performance of an animal based on observed and measured traits. Better when based on an unbiased set of complex equations looking at data on thousands of animals. Not perfect, but a very good tool. My thoughts on selection. Make initial selections based on what you see. Then finetune those selections based on the EPD's (remove the culls from your selections). Probably can do it in the reverse order just as well as long as you do both. Always consider the EPD accuracy as well as the number. Knowledge of the cow family is always important as well.</p><p></p><p>Some people believe that the breed association manipulates the numbers to someone's advantage. I don't subscribe to the conspiracy theory. They are trying to make the models better and better. I think most of the "manipulation" is unintentional and comes from the breeders when they don't submit data on all their animals. There have also been attempts to manipulate EPD's by submitting false data on a bull's calves which have limited use among a few people. There will always be those who try to cheat the system.</p><p></p><p>I got wordy again, didn't I?</p></blockquote><p></p>
[QUOTE="simme, post: 1658398, member: 40418"] Keep in mind that the calculation of EPD's is very complex. The explanation that I offered above is a very simplistic rough view because that is about as far as my understanding goes when you get into the deep details. Mathematical/statistical models are very complex. With EPD's, there are some traits that are inter-related to other traits. The models must take the physical measured and observed data and correctly/best assign it to an EPD trait. For instance, weaning weight is easily measured. But what portion is due to the milk quantity and milk quality of the dam and what portion is due to the growth ability of the animal? How much growth came from the dam and how much from the sire? The complex mathematical models attempt to resolve all that. The weaning weights on your five bulls all being inputs to the model resulting in updated EPD's not only to your 5 bulls, but to all the contributing animals in their pedigree back for generations. I expect that for these complex relationships the models have to be run thousands of times until the numbers all finally converge. Each run using intermediate results from the previous run until the final numbers remain the same. When EPD's were developed many years ago, the computing ability and cost dictated that the EPD's were only updated once or twice a year - due to effort and cost. I think now they can be updated daily. Some people don't put any value in EPD's and some perhaps put too much faith in them. But, I believe they should be one of the tools used. Most any cow/calf person with at least a few cows can name/identify their best or better cows. They know which cows wean the heavier calves year after year. Which cows have higher BW calves and which cows have lower birth weight calves. Which milk better than the others. All based on observation and measurement. If you sell your calves at the auction barn, you can read the weights on the statement. That in a simple nutshell is the principle behind EPD's. Predicting the performance of an animal based on observed and measured traits. Better when based on an unbiased set of complex equations looking at data on thousands of animals. Not perfect, but a very good tool. My thoughts on selection. Make initial selections based on what you see. Then finetune those selections based on the EPD's (remove the culls from your selections). Probably can do it in the reverse order just as well as long as you do both. Always consider the EPD accuracy as well as the number. Knowledge of the cow family is always important as well. Some people believe that the breed association manipulates the numbers to someone's advantage. I don't subscribe to the conspiracy theory. They are trying to make the models better and better. I think most of the "manipulation" is unintentional and comes from the breeders when they don't submit data on all their animals. There have also been attempts to manipulate EPD's by submitting false data on a bull's calves which have limited use among a few people. There will always be those who try to cheat the system. I got wordy again, didn't I? [/QUOTE]
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