Improved breeding value calculations for Norwegian Red
The methods for calculating breeding values (BVs) for Norwegian Reds have now been improved and are reflected in August 2018 proofs. Genomic BVs have 2% to 3% improved reliability compared to the past and most BVs on genomic selected (GS) sires are lower and closer to BVs for daughter proven bulls.
The newest improvements will increase reliabilities of sire BVs by another 2 to 3%. The new improvements include:
1. Increase in number of genetic markers used for many animals along with improved usage of genomic pedigrees in genetic evaluation procedures.
2. Improved grouping of imported sires, herd bulls and other animals with missing pedigree or unknown parents in genetic evaluation procedure.
3. Change from a base population defined by daughter proven sires to a cow base with initial cows born in 2010 through 2014 used for the new base definition. Average BVs for cows born in these 5 years is defined as the base and set to 0.0.
4. Standardization of BVs is now done using a standard deviation of 12. Standardization is based on a function of the BVs from cows that are used in defining the base population.
The result of these combined improvements resulted in lower BVs for genomic selected (GS) sires that are closer to the top daughter proven sire BVs. (See scatter plots below where each dot represents a single GS sire's BV in April and August 2018.) Other breeding programs that have implemented similar changes to genetic evaluation models have also experienced a lowering of GS sire BVs to be more like that of daughter proven sires. Total Merit Index (TMI) of individual bulls on average was lowered significantly due to lowering of BVs for traits contributing to TMI. However, many top GS bulls in April 2018 still rank at the top for TMI in August making a group of young bulls the best choice for improved genetic gain.
Geno has a long history of a successful breeding program in the Norwegian Red. Progeny tests results for production, fertility and health traits have been used for selection in the Norwegian Red since the 1970s. Historically the top progeny tested sires were used in about 60-65% of the population and young bulls were used in the rest of the population. About 125 young bulls were progeny tested each year using a strategy to result in large first crop daughter groups (250 daughters).
Until 2013, pedigree information and young bull performance was utilized to choose the young bulls to be progeny tested. Beginning in 2013, Geno began the use of genomic information for the preselection of young sires to be progeny tested. The genomic information on sires in 2013 was calculated using the 2-step approach that is utilized by most other dairy cattle breeding programs. In February 2016, the first version of the single-step genetic evaluation procedure was implemented for use in calculating BVs for Norwegian Reds. During 2016 Norwegian farmers fully adopted the use of genomic selected sires and discontinued use of daughter proven sires. The rate of genetic gain has increased dramatically since these developments mainly due to the dramatic reduction in generation interval.
The single-step genetic evaluation procedure eliminated many problems associated with the traditional 2-step process. However, it was still possible to improve on the initial single-step approach. Initial results from the single-step procedure indicated that comparing older, non-genotyped animals with the more current animals with genotypes was flawed because of selection. The newest improvements eliminated this bias.
Reliabilities for most traits from the single-step genetic evaluation procedure has generally ranged from 0.50 to 0.65. Reliabilities have increased slightly in recent genetic evaluation runs due to the addition of more genotypes.
(Click on the illustration to view a larger image)