What is a correlation? Why is it important to talk about correlations in breeding?
Correlation is a measure for how things are related. When the connection between two things is close, we talk about a high correlation. On the contrary, when the connection is not clear, we talk about a low correlation or no correlation at all in some cases.
Why are correlations useful within breeding? Correlations are useful because if we find out what relationship exists between two things, we can make predictions about their future development. This way, we can calculate more precisely about the genetic progress that can be achieved. Understanding correlations is an important part of breeding programs.
A correlation coefficient, a number that indicates the strength and type of correlation, is a way to put a value to the relationship existing between two things. Correlation coefficient is a value of between -1 and 1. Number 0 means there is no relationship between the two variables at all. Perfect negative correlation has a value of -1 and perfect positive correlation is marked with 1. Negative correlation means that if one of the variables is increasing, the other variable is decreasing. For example, like the relationship between production index and health traits. In positive correlation, both variables are increasing.
We have talked in our earlier posts that there are 15 main traits in NTM. From the data we are collecting on all the different traits included in NTM, we can see that NTM has a strong positive correlation to Longevity, Production, General Health (trait that covers reproductive & metabolic disorders, feet & leg problems), Daughter Fertility and Udder Health.
The picture shows the five traits that you achieve most progress for, when you rely on NTM as your breeding tool for VikingHolstein. It’s important to remember that with NTM you are always breeding for improved profit as well. Data shows, that selecting bulls with high NTM, gives progress in all traits that have economic importance for a successful dairy business.
In a way, correlations are like ‘quality guarantee certificates’ that tell you what traits you improve in your herd, and in what traits you achieve genetic progress when you use NTM guiding your breeding strategy. Therefore, correlations are important to show and talk about.
In our next post, we will explain in more detail the trait correlations in relation to NTM.