Although some traits have low heritability, genetics still drive valuable improvements over time. NZ Animal Evaluation scientist Rhiannon Handcock explains.
Inside Dairy
2 min read
Breeding Worth ensures a balanced focus, giving attention to economically important traits, even those with lower heritability.
Heritability measures the proportion of variation in a trait that is due to genetics rather than environmental factors. It is expressed from 0 to 100%, where 0 means all variation is due to environmental factors, and 100% means all variation is genetic. Traits with higher heritability respond more quickly to selection, while traits with lower heritability improve at a slower pace.
By knowing the heritability of specific traits, breeders can make more informed decisions. Farmers might tend to focus on more heritable traits, as these often show progress more quickly. However, this approach can sometimes overlook valuable low heritability traits.
An index like Breeding Worth (BW) helps maintain a balanced focus, ensuring that economically important traits with lower heritability still receive the attention they deserve.
Low-heritability traits, such as survival (2%), calving difficulty (2%) and fertility (between 2 and 10%) improve slowly over generations, yet they are crucial for overall herd productivity and wellbeing.
In contrast, high-heritability traits, such as liveweight (60%), gestation length (50%) and milk production (30%), are more responsive to selection, showing faster genetic gains.
Fertility is a good example of a low-heritability trait that is still important to select for. While its low heritability suggests genetic improvement can be challenging, research from DairyNZ’s Pillars of a New Dairy System programme demonstrated clear differences in reproductive performance between heifers with high (+5) and low (-5) fertility breeding values (BVs) under the same management.
Heifers with higher BVs consistently achieved significantly better reproductive outcomes than those with lower BVs, including a 30% difference in their 6-week in-calf rates in each of their first two lactations. The research highlighted that even a low-heritability trait like fertility can still significantly influence farm outcomes.
Heritability helps us understand how quickly traits can be improved through selection.
Importantly, even low-heritability traits like fertility and survival are worth the investment as the progress compounds over each generation.
Small genetic improvements can often lead to long-term herd-level benefits.
There's no value in focusing on low heritability traits such as fertility.
While progress with low-heritability traits may be gradual, each small gain accumulates across generations, ultimately leading to meaningful change.
This article was originally published in Inside Dairy February-April 2025.
