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- Inbreeding vs. Genetic Progress
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- Recumbency in Holstein Calves
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As the rate of inbreeding increases, there is increasing concern about future genetic diversity in the global dairy population. Although there is no denying that inbreeding is on the rise, genetic progress has also increased at unprecedented rates during the past decade. While genetic progress cannot be the only goal, focusing solely on lower inbreeding will not compensate for low genetic values. A careful balance between genetic progress and inbreeding must be achieved to optimize long term profitability and sustainability of dairy cattle.
Frequently Asked Questions
What level of inbreeding is safe for my herd?
The “safe” level will vary by animal and by herd based on the amount of homozygosity (like genes) inherited from recent common ancestors and their detrimental impacts. Old inbreeding (originated from remote common ancestors) is usually less harmful as deleterious genes are purged over time. Recent inbreeding is of more concern. The overall inbreeding coefficient does not tell us what is safe or dangerous, as the picture is incomplete and does not tell us whether the common genes improve performance or are detrimental. We need the analysis of the genome to tell us more about age of inbreeding.
Does this mean that I can use bulls that are highly inbred in my herd without problems?
Relationship of the bull to the herd is a more important factor than inbreeding of the bull. It is best to use sires with lower relationship when possible, but inbreeding control must always be balanced with genetic progress. Just because an individual bull is more inbred, does not mean that he will cause higher inbreeding within a particular herd if the herd has used unrelated bulls in the past. An example that I always use goes back to O-MAN in my dad’s herd. We never used O-MAN because my dad did not like the Manfred daughters that we milked. Based on the population as a whole, O-MAN sons would have had a high inbreeding coefficient. However, for our herd, they could be freely used. We cannot assume that inbred relative to the population necessarily means inbred relative to the herd (or the individual animal).
Is inbreeding today less dangerous than it was 20 years ago?
With all that we know through genomics today, inbreeding is less risky than it used to be, as we can identify detrimental genes like recessives and negative haplotypes earlier in the animal’s life. New deleterious mutations are also identified much faster. This allows us to either eliminate the use of the animal for breeding purposes, or to make more educated breeding decisions to prevent mating of carrier animals. Because we are marketing young genomic sires with no progeny record, there is some risk of unknown new mutations, as mutations are usually only detected after spreading through the population for few generations.
What is the difference between GFI and EFI?
GFI is Genomic Future Inbreeding. EFI is Estimated Future Inbreeding calculated from pedigree. Both GFI and EFI are measure of proportion of genes in common between individuals due to common ancestors. GFI tends to be higher and more accurate than EFI in most cases because GFI is looking at the genes but EFI looking at probability of gene inheritance through the pedigree.
Why does it seem like the highest-ranking bulls have higher inbreeding?
When we select intensively for specific traits generation after generation, we are selecting for the good genes that produce those traits, which results in more common genes. Higher genomic inbreeding is partly a result of faster genetic progress, as the highest-ranking animals tend to have similar genes for the trait under selection.
How is SSI/WWS going to maintain a level of diversity in the genetic program if we are only selecting for the best genetics?
SSI/WWS is dedicated to supplying genetics to a global market. This requires diversity in the type of genetics within our bull population, as different markets and management systems have different genetic needs. The size of our bull population sampled from large number of herds, as well as the diverse needs of our customers, helps us to maintain diversity in our genetic portfolio, especially when compared to many of our competitors.
What is currently being done to balance genetic progress with the detrimental impact of inbreeding?
For years, CDCB has adjusted PTA values based on the inbreeding regression factors (see Table below). For every percentage point change in inbreeding compared to the base population, a regression factor is applied. The value of the regression factors are based on the economic impacts of inbreeding as estimated by CDCB. As bulls age and have more sons and grandsons in the population, their relationship to the population increases.
Example: 7HO15167 GAMEDAY at 10.1% EFI
10.1% (GAMEDAY EFI) – 7.4% (Holstein Base) = 2.7%
Milk Regression = -72.9 x 2.7 = -196.83 pounds of milk
GAMEDAY’s official proof = 809 PTA Milk
GAMEDAY’s genetic value (without regression for inbreeding) = 1005.83 Milk
Summary
As we work toward genetic progress it is important to remember that PTA values have already been adjusted for inbreeding. Therefore, while low inbreeding is preferred, reducing inbreeding will not, compensate for low genetic values (see example below). 
At one time, SUPERSIRE was somewhat of an outcross sire, but his EFI has increased due to his genetic superiority and resulting popularity as a sire of sons. Today SUPERSIRE is 5.7% higher EFI than GW ATWOOD. However, even with significantly higher EFI, SUPRESIRE daughters are expected to have significantly higher lifetime profitability than the daughters of GW ATWOOD.
World Wide Sires has a variety of tools designed to help producers maintain genetic diversity in their herds while maximizing genetic progress.