The implementation of genomic evaluations has increased the reliability of genetic evaluations. Current gains in reliability (%) due to genomic for young bulls for production traits are 33, 22, and 14 resulting in reliabilities 73, 62, and 53 of for Holsteins, Jerseys, and Brown Swiss, respectively. A genomically tested young bull has about the same reliability as a proven bull did previously. This may cause heaver use of young bull semen because producers can use them with more confidence. Higher use of young sires and higher selection intensity on parents of bulls (due to genomic selection) would also increase the genetic gains.
- Percentage of inseminations by breeding year, service sire age, and breed
- Brown Swiss
- Percentage of young bulls (age 0.8-3.9) that were genotyped by year and breed
- There was an increased use of young sire semen for Holsteins and Jerseys between 2006 and 2010, with the Holsteins having the largest increase at 13 percentage units. This was an expected result due do the larger gains in genomics for the Holstein breed. Brown Swiss did not show much change, probably due to the lower gains in reliability from genomics.
- Older sires remained constant across time ranging from 14-19% for Holsteins, 16-24% for Jerseys, and 28-35% for Brown Swiss.
- The first-crop sire group saw the largest reduction for the Holsteins with a decrease of 9 percentage units between 2006 and 2010.
- The percentage of young bulls genotyped increased drastically from 2008 to 2010 and is now above 97% for all 3 breeds.
- The median percentile ranking for available young bulls rank for $Net Merit was 88%, 82%, and 81% for Holsteins, Jersey and Brown Swiss (the average of proven bulls is 50%) .
- The proportion of young bulls that are genotyped and then marketed (AI status=G) is 4% for Holstein, 10% for Jersey and 7% for Brown Swiss.
- The progress per generation based on the simulation was 0.23 before genomics for the Holsteins and was 0.43 after genomics (with the use of 95% young bulls).
- The simulation showed that the optimum use of young sire semen was above 95% for Holsteins, Brown Swiss, and Jersey.
- To investigate the use of young bulls over the last five years to quantify changes in bull semen use that might be attributed to the advent of genomic evaluations
- To investigate the optimum level of young bull use given the current genomic evaluation situation
- MATERIALS AND METHODS
- Brown Swiss, Jersey, and Holstein insemination records from January 2006 through December 2010 obtained from the dairy records processing centers
- Service sire age (at time of insemination) included 3 age groups: young (0.8-3.9 yr), first-crop (4.0-7.9 yr) and old (≥8.0 yr)
- Genomic status was determined at the time of insemination and the date of genotyping of the bull. Bulls that were genotyped before official releases (April 2008 for Holsteins and Jerseys and August 2008 for Brown Swiss) were set to non-genotyped until the official release.
- Net Merit ($) and corresponding percentile ranks were based from the USDA official April 2011 genetic evaluation
- A simulation was conducted to determine optimum levels of young bull use. The four pathway method was used which consisted of sire of sire, sire of dam, dam of sire, and dam of dam pathways. The assumptions used were based on data (where available), literature, or in a few cases best guess. Genetic gains by generation interval were compared to identify the optimum level of young bull use.
- Number of Inseminations by breed and year
Breeding companies are continuing to adapt their protocols and young bull buying criteria accordingly. All of this has led a higher emphasis of marketing young bulls and to an increase in the use of young bulls in the United States. Simulation studies indicate that even more young bull should be used to optimize genetic gains. Similarly, use of heifers instead of cows as bull dams is recommended.