Basics of dairy cattle breeding
Knowing the genetic merit of your herd is a key component to successfully improving traits of importance on your farm. The observed performance (e.g. 305 day milk yield) of an individual cow depends on two things:
a) the genetic merit of the cows
b) the environment in which she is performing
Genetic evaluations attempt to disentangle the effects of genes and the environment in order to select animals that have high genetic merit, and not those that perform well simply because they are well managed and fed. For example, if Cow X has a much higher genetic merit for milk yield than Cow Y, Cow Y will need much more feed to milk the same as cow X. Alternatively, if Cow X and Y are fed the same, Cow X will outperform Cow Y for milk yield. Genetic evaluations allow us to directly compare animals that are performing in many environments, by removing the part of the observed performance that is due to the environment and management of the cows.
We cannot directly alter the genetic merit of an individual cow, however improvements can be made for specific traits in the offspring of the cow provided she is bred to a sire that is better than she is for those traits.
Therefore it is important to know both the genetic merit of the cow and the sire in order to make genetic improvements in traits of economic importance Genetic evaluations are expressed relative to a base cow which represents the national average cow in the base year. To make improvement the very best bulls for the traits of interest should be used, e.g a cow with a poorer calving interval bred to a higher fertility focused High EBI sire or a cow with poorer production being matched to a higher production sub-index sire.
Base Cow Production
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