Date of this Version
The chief advantages of sire evaluation based on five-month daughter records are: 1. Genetic progress is inversely proportional to the turnover rate in testing bulls so that if this interval is shortened by 10%, the rate of genetic progress will be increased by 11%. The turnover period can be shortened with the use of 5-month records from about 50 months to 45 months—a decrease of 10% in time. 2. Genetic progress is also related to how many top bulls are saved and how many poor ones are culled out of all those sampled. In other words, the more bulls tested with the same number saved for use, then the faster the progress which can be made. The shorter length of time which bulls have to be saved with five-month record evaluation can allow up to 10% more bulls to be tested with the same physical layout. 3. Returning a superior sire to service 5–6 months earlier will allow an increased service life for those sires. This could increase the service period by 15% and would also reduce the overhead costs to the stud as well as allow the dairyman the services of a superior bull for a few extra months. Some problems to be solved to enable bull studs to make practical use of five-month records are: 1. Suitable mature equivalent factors must be determined for all breeds for five-month records. 2. Breed averages for five-month records must be established. 3. The regression of daughter records on stablemate averages must be estimated. 4. Estimates of variance and covariance components used in the procedures must be confirmed from larger numbers of observations. 5. The importance of differential persistency between sire groups should be investigated.