A revision of breeding values is not unusual. Often this is done to refocus a breeding value or to include newly implemented breeding values with overriding importance for the breed in an index. In the case of the RZG, both aspects can be mentioned as reasons and are to be understood as a consistent further development of the total merit index towards more animal welfare.
What is new in the RZG?
The composition of the new RZG
With the reweighting of the overall index, the health breeding values RZhealth and RZcalfhealth published in 2019 are now also taken into account. Furthermore, in addition to feet and legs and udder, the trait complex body is also included in the RZG. An observation of the development of important body traits in the population led to this step.
While the RZhealth is newly included in the RZG, the milk production (RZM), the longevity (RZN) and the fertility (RZR) lose weight in benefit to the health breeding values. Since the RZhealth can be used to directly improve animal health through breeding, the importance of the previously used secondary traits for animal health (RZS, RZR and RZN) decreases. The RZN and RZR are positively influenced indirectly via the RZhealth. As a result, the reduction of the weight percentages in the index does not have a negative effect on the development of the traits. The removal of the breeding value for Somatic cell Score (RZS) is performed in favour of the mastitis breeding value in RZhealth. The RZhealth more directly reflects and influences udder health.
The reduction of the RZM in the RZG allows a stronger focus on functional traits in the already high performing German Holsteins without compromising the economic importance of this breeding value. Overall, a breeding improvement in animal welfare can therefore be achieved.”