Total merit indexes - NTM vs. RZG

Total merit indexes like NTM (Nordic Total Merit), TPI, NM$ index, PLI, BPI, RZG among others are important genetic selection tools. The indexes differ by the traits covered and by the weight allocated to the specific traits. Let’s look at the traits included in the German total merit index RZG and NTM and compare the weights of different traits for Holstein. 
NTM places 52% of the total weight on health, reproduction traits and longevity, while RZG puts 40%. NTM has the traits that are not covered by RZG – Hoof health (3%), General health (4%), Calving direct (6%), Youngstock survival, calf survival in the early and late rearing periods (5%). Daughter fertility has similar weights in RZG and NTM, while Udder health and Calving maternal have significantly higher weight in NTM. It is important to note that Udder health index in NTM is based on the registrations of clinical mastitis – direct selection, while RZG use SCS as indirect selection tool. RZG has higher weight on longevity (20%), as RZG does not have most of the health traits that are included in NTM, so Longevity is used as indirect selection tool for better health in RZG.
As for production, RZG has higher weight on Production 45%, while NTM has lower weight on Production traits – 30% with Production (28%) and Growth (2%). 

If we look at conformation traits, overall RZG and NTM have similar weights on conformation. RZG has a slightly higher weight on Feet & Legs and Udder conformation has similar weight in NTM and RZG. Milkability and Temperament are not included in RZG. 
 Trait
 NTM
 RZG
 Production
 28
 45
 Growth
 2
 -
 Daughter Fertility
 11
 10
 Calving Direct
 6
 -
 Calving Maternal
 6
 3
 Udder Health / SCS
 13
 7
 General Health
 4
 -
 Hoof Health
 3
 -
 Longevity
 4
 20
 Youngstock Survival
 5
 -
 Feed Efficiency
 -
 -
 Frame
 0
 0
 Feet & Legs
 4
 7
 Udder
 9
 8
 Milkability
 3
 -
 Temperament
 1
 -

All in all, NTM includes 14 main traits, while RZG has seven traits. NTM offers extra when it comes to health and reproduction traits compared to RZG and this group of traits has high economic importance for achieving profitable and sustainable dairy production. 

With higher weight placed on health and reproduction traits and the focus on direct selection in general and for health traits in particular, NTM is a much stronger and more reliable tool for commercial dairy farmers, as NTM delivers the well-balanced breeding goal for improving production, health, reproduction performance and functional conformation. 

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