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The new RZG

The key to better health and performance of dairy herds worldwide

The April sire Summary 2021, shows the German Total Merit Index, RZG, published in a new combination. The last revision took place in 2008. The RZG (Relativ Zuchtwert Gesamt) is applied to improve all traits according to their relative importance in the overall breeding goal. Starting in April 2021, the German health breeding values, RZhealth and RZcalffit, which have been increasingly influencing bull selection on farms since their introduction in 2019, are now directly included. In the past, the cows’ health has been considered within the RZG via secondary traits such as the RZS (Somatic Cell Count), the RZR (Reproduction Index) and the RZN (Functional Herd life Index). The RZM (Milk Production Index) is reduced to a weight of 36 % which is still ahead of the health breeding values but remains the most important trait within the new RZG. Today’s excellent milk production recorded in the German Holstein population, allows a shift in weighting towards more health, which additionally brings economic advantages by avoiding treatment costs and performance losses due to diseases. With this new revision of the Total Merit, Germany sets out a clear focus, with emphasis on animal health and animal welfare.

Total merit index RZG - Composition - April, 2021
Total merit index RZG – Composition – April, 2021

Inclusion RZhealth

As the RZhealth is a direct trait for udder health, the secondary trait RZS from the RZG have been removed. In addition, RZN and RZR lose weight in favor of RZhealth and RZcalfhealth. The two new breeding values have a positive effect on these traits. Therefore, their lower weighting will not reduce the breeding progress for longevity and udder health

Inclusion of the complex body

Other minor changes are extended at the complex “body”. So the index can account for the fact that body structure plays a key role for the functionality of a cow. Extreme characteristics like excessive stature are respected negatively. In addition, the maternal calving trait RZKm is supplemented by the direct calving trait RZKd. Within both calving traits the weighting for stillbirth has been increased. This adjustment was made due to the fact that stillbirths have a higher variance and therefore a higher information value. There is also a high correlation between stillbirth and calving ease. The new weighting is resulting in minor changes in the calving values of the bulls. All included traits and their relative weights within the RZG are shown in the diagram above.

RZG – modern dairy farming

To summarize, the new RZG enables farmers to breed specifically for high milk yields and good health of their animals. Wich furthermore meets the changing demands of modern dairy farming. The new RZG remains standardized to a mean of 100 in the base*. The genetic standard deviation still is of 12 points.

 

*cow base with all cows who are 4-6 years old, born 2015-2017

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