Individual Herd Heritability Estimates using ASReml

Herd heritability is an important issue in animal breeding; it measures the genetic and environmental influences on the development of a specific quantitative trait. Big words, with big meanings….but for cattle breeders it’s important to understand which aspects of the cattle are influenced by genetics and which by environmental factors. Understanding the genetic similarity between generations makes for a better planned breeding system.

Chad Dechow, an ASReml user from the Department of Dairy and Animal Science at The Pennsylvania State University, studied herd heritability estimates in over 20,000 herds. He and his colleagues compared covariance parameter estimates in subsets of data, pooled from herds with high, medium or low individual herd heritability estimates. The individual herd heritability estimates, generated from a regression model using ASReml, applied to milk yield, fat yield, protein yield and somatic cell score. These regression techniques stratified the herds by heritability; additive genetic variance increased progressively and permanent environmental variance decreased as herd heritability increased. Future work by the same authors demonstrated that herds with low heritability had a high rate of parent misidentification and that such herds were poor candidates for genetic testing herds.

“We used ASReml,” says Chad, “because it is a very flexible mixed models program that is capable of analyzing large datasets in a very efficient manner.”

ASReml was used to generate individual herd heritabilities; the model and results can be seen in the original paper published in The Journal of Dairy Science 2008. 91:1648-1651

It’s important for breeders to know which factors are genetic and which are affected by environment, for example health events have low heritability indicating that improved management would be important in improving animal health, rather than genetic selection. Understanding which factors can be changed by genetic selection and which through environmental influences is vital as it means that breeders and farmers can plan and manage their herds more effectively; as they understand which aspects can be changed through a breeding programme and which through environmental factors. As heritability differs so significantly between different traits it’s again vital to understand which aspects are most likely to be changed through a breeding program; the higher the heritability a trait is, the more quickly it can be changed through genetic selection; again helping breeders and farmers to plan better, as it can indicate timescales for any genetic changes to take place.

There is no doubt that, as with many things in life, the better understood something is the more effective the planning will be. Research, such as Chad’s is vital to help cattle breeders and farmers breed and manage their herds more effectively. And all good research needs support and suitable tools; ASReml is such a tool. Software that was developed by researchers in animal and crop breeding, it is highly suited to this purpose providing users with the ability to obtain reliable predictions of genetic values. Research needs trustworthy and reliable tools and ASReml is a great fit for the job.

Thanks to Chad Dechow for his help on this piece. The full paper is available here.

Also of interest:

Chad is the editor of The Specht Report – a report on breeding performance.


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