I can tell you the number of times I have seen top breeders spend hours upon hours deciding who to mate their top cattle. While I understand the importance of this decision, often times I find that the final decision is based on traits that are so low in heritability the chance of actually improving the cow for that trait is extremely low. As a result, the mating they were hoping to give them that next great one, turns out to be a field of dreams.
What is Heritability?
Heritability is a measure of the degree (0 to 100%) to which offspring resemble their parents for a specific trait. This definition can be extended to all genetic relationships such as half sisters sired by the same bull. Heritability measures the strength of the relationship between performance (phenotype) and breeding value (genotype) of an individual animal. Recall that “heritability” applies to a specific trait measured in a specific population of animals at a specific point in time. If the same trait is measured in a slightly different way in some other group of animals, the estimate of heritability can be expected to be different.
Why Should You Care About Heritability?
Heritability tells you the breeder how much confidence to place in the phenotypic performance of an animal when choosing parents of the next generation. For highly heritable traits where heritability exceeds 0.35, the animal’s phenotype is a good indicator of genetic merit or breeding value. For lowly heritable traits, where heritability is below 0.15, an animal’s performance is much less useful in identifying the individuals with the best genes for the trait.
This is where the problem lies. The following is a breakdown of High vs Low heritability traits.
| High | Medium | Low |
| Milk Yield (0.43) | Fat Yield (0.34) | Herd Life (0.10) |
| Protein Yield (40) | Somatic Cell Score (0.27) | Calving Ability (0.6) |
| Fat Percentage (est. 0.50) | Milking Speed (0.21) | Daughter Calving Ability (0.6) |
| Protein Percentage (est. 0.50) | Conformation (0.26) | Milking Temperament (0.13) |
| Lactation Persistency (0.40) | Rump (0.23) | Daughter Fertility (0.7) |
| Dairy Strength (0.36) | Mammary System (0.25) | Feet & Legs (0.15) |
What Should You Do About Traits With Low Heritabilities?
Heritability can tell us how closely genetic merit follows phenotypic performance, but it tells us nothing about the economic value of better performance. Some traits with low heritabilities, such as the survival and fitness have low heritabilities but high economic value. Other traits, like stature, are moderately to highly heritable, but have insufficient economic value to be given much emphasis in selection programs. Low heritable traits of substantial economic value should always be targeted for improvement through better environmental conditions. This often has the most direct impact and often can be done much quicker than through breeding programs.
The dairy industry is increasingly interested in genetic improvement of health, fitness, survival, and reproductive traits. Milk production is more heritable than these traits, and genetic gains in milk production for the last 30 years have been substantial. Perhaps part of the reason for increased emphasis on equally valuable traits of lower heritability has been the genetic progress made in milk production. Many farmers feel that their cows have more genetic ability to produce than can be utilized efficiently on many dairy farms. The relative economic value of the fitness traits and milk production appears to have changed and selection objectives will change as well.
What is the Heritability of Type Traits?
As the follow table shows. Trying to improve feet and legs is often better served through management than breeding, while stature and body depth would show a more rapid genetic gain.
| Stature | 0.42 |
| Strength | 0.31 |
| Body Depth | 0.37 |
| Dairy Form | 0.29 |
| Rump Angle | 0.33 |
| Thurl Width | 0.26 |
| Rear Legs Side View | 0.11 |
| Foot Angle | 0.15 |
| Feet and Leg Score | 0.17 |
| Fore Udder Attachment | 0.29 |
| Rear Udder Height | 0.28 |
| Udder Cleft | 0.24 |
| Udder Depth | 0.28 |
| Front Teat Placement | 0.26 |
| Teat Length | 0.26 |
| Final Score | 0.29 |
The Bullvine Bottom Line
Heritability is one of the most important concepts when it comes to your breeding program. There are several working definitions, as heritability is used to help plan breeding programs, determine management strategies, estimate breeding values of individual animals, and predict response to selection. In general, traits related to fertility, fitness, health and survival have low heritabilities of less than 0.15. Production traits like milk or protein yield are moderately heritable, with values from 0.15 to about 0.40. So if you are looking to see significant gains from your breeding programs it’s best to focus on highly heritable traits, otherwise your breeding program is more of a field of dreams.
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Traits needs to be evaluated accurately to be highly heritable. Most anyone can measure the stature of a cow… thus you can easily and accurately measure it..Stature can be effected by poor feeding and management, but less than most.
However with Somatic Cell Score for example it is difficult to measure between herds because of management effects..However in an average managent herd …the difference between cows on test is very heritable. .Basically the old 80% management between herds ….80% genetics within your herd!. Within your herd is most important anyway.
I would question the statement “In general, traits related to fertility, fitness, health and survival have low heritabilities”. Around the world we see national breeding programs based on female fertility (most promemently in New Zealand and Ireland) The use of bulls with high daughter fertility indexes in these countries has seen huge improvements in daugher fertility phenotypes(see http://www.icbf.com for more details). However these are completely different production systems to the US and Canada and the genetic merit is being allowed to be expressed since the cows arent being “pushed” in the same way. Likewise if you put a herd of Canadian Holstiens on a New Zealand farm practicing Golfball Grazing you wouldnt see their milk potenial being realised