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Total Merit Index

Total Merit Index

Each year the highest ranking Norwegian Red bulls, based on their total merit index (TMI), are selected and used as elite sires in Norway and internationally. Both genomic proven bulls and progeny proven bulls will be available for use.

Ten trait groups are included in the current TMI (Table 1), with production traits, udder health, fertility and udder conformation receiving the highest relative weights within the TMI.

Development of the Norwegian Red TMI 

Figure 1 shows how the relative weights on different traits have changed over time. In the 1960's, 70% of the weight was milk production. During the 1970's a national database was developed which included all health and fertility data. This allowed for health and fertility to be included in the TMI beginning in the 1970s. Since then the relative weight on health and fertility have gradually increased while the relative weight on production traits has decreased.


Figure 1. 

Breeding goal

click on the illustration to see a larger image. 


The highest relative weighted traits in the TMI (Table 1) are milk production traits, udder health, fertility and udder conformation. Simultaneous genetic improvement for health, fertility and production traits over time is well documented. This has been obtained due to the weight on these traits in the TMI, and due to their economic importance for the farmer.


Table 1: Relative weights on traits included in the TMI of Norwegian Red sires.

Traits Relative weight
Milk production index 28
Udder health 18
Fertility 18
Udder conformation  18
Beef index (males) 6
Diseases other than mastitis 4
Claw health 4
Foot and leg conformation 2
Temperament 1
Calving ease 0.5
Stillbirth 0.5


Milk production index

The milk production index is based on data from the Norwegian Dairy Herd Recording System (see info to the right). 


The milk production index includes several traits.


Trait Relative weight (%) Heritability
Kg milk  5 0.28
Kg fat 47.5 0.21
Kg protein 47.5 0.24
Protein (%) Not included -
Fat (%) Not included -


The relative weight is how much each trait affects the value of the milk production index.

Udder health

Udder health (mastitis) causes the greatest economic losses of any disease in dairy cattle. Resistance to mastitis has been included in the TMI since 1978 with gradually increasing emphasis. From 1990, the emphasis increased and this has caused both phenotypic and genetic progress in resistance to mastitis in the Norwegian Red population. Genetic progress in resistance to mastitis allows Norway to be the country with the lowest use of antibiotics worldwide.


Here are the relative weights for clinical mastitis and somatic cell count in the udder health index.


Trait  Relative weight (%) Heritability
Somatic cell count 40 0.13
Clinical mastitis 60 0.04


The fertility index has recently been improved by replacing non-return rate with number of inseminations. The new trait reflects the number of inseminations that a cow needs to become pregnant. Number of inseminations is biologically very similar to non-return rate, but it has more genetic variation since really bad cows with five inseminations get punished more heavily than cows with just one unsuccessful insemination.


The fertility index consists of three traits with the weights as indicated in the following table.


Trait Relative weight (%)
Number of inseminations, heifer 22
Number of inseminations, cow 45
Calving to first insemination  33


Fertility was first included in the Norwegian Red breeding program in 1971.  The Norwegian Red is likely the most fertile breed of dairy cattle in the world due to selection for increased fertility for over the last 40 years.

Udder conformation

Udder conformation traits are scored by breeding advisors using a linear scale. The udder trait definitions are harmonized with populations in other countries.


The udder conformation index consists of several traits with the weights as indicated in the following table.


Trait Relative weight (%) Heritability
Fore udder attachment 20 0.11
Rear udder width 5 0.13
Rear udder height 8 0.11
Central ligament 12 0.10
Udder depth 20 0.24
Teat length 5 0.27
Teat thickness/diameter 5 0.20
Front teat placement 7 0.18
Rear teat placement 8 0.22
Udder balance 10 0.11 

Foot and leg conformation

Breeding advisors record foot and leg conformation traits together with other conformation traits. The foot and leg conformation traits are rear legs rear view, foot angle and rear legs side view.


The following table shows the relative weight for the traits in the foot and leg conformation index and their heritability.


Trait Relative weight (%) Heritability
Rear legs side view  Not included  0.09
Rear legs rear view 50 0.07
Foot angle 50 0.09

Claw Health index

Claw disorders are recorded at claw trimming by professional claw trimmers or farmers. Three claw disorders are included in the claw health index.

  • Corkscrew claw
  • Infectious claw disorders
  • Laminitis-related claw disorders

Corkscrew claw

The cow is recorded as affected if the claw is mild to severely twisted.

Infectious claw disorders

Infectious claw disorders are a group of single claw disorders, including interdigital dermatitis, digital dermatitis, heel horn erosion and interdigital phlegmon (foot rot).

Laminitis-related claw disorders

Laminitis-related claw disorders are a group of single claw disorders, including sole ulcer, sole hemorrhage, toe ulcer, white line fissure and white line abscess.


The table shows the relative weight of the traits in the claw health index and their heritability.


Claw health index
Trait Relative weight % Heritability
Corkscrew claw 50 0.06
Infectious claw disorders 30 0.03
Laminitis related claw disorders 20 0.02

Beef index (males)

The beef index is made up of 3 traits, and measured on bulls fed for beef.

The weights for the traits in the beef index are indicated in the following table.


Trait Relative weight (%) Heritability

Slaughter weight (growth rate)

60 0.15

Slaughter classification (EUROP scoring)

20 0.19

Fat grading

20 0.17


This trait is observed on the heifers and cows and reported to the Norwegian Dairy Herd Recording System by farmers. They use a scale of 1 to 3, whereas 1 is very calm, 2 is normal and 3 is nervous/aggressive.

Diseases other than mastitis

Much progress has been made in the genetic improvement of the Norwegian Red for resistance to diseases other than mastitis. Currently 6 diseases are included in the index:

  • Ketosis
  • Milk fever
  • Retained placenta
  • Cystic ovaries
  • Metritis
  • Silent heat

Ketosis, milk fever and retained placenta are the most common diseases (except for mastitis) so they contribute the most to the index for diseases other than mastitis.

Calving difficulty and stillbirth

These traits have been included in the TMI since 1978.


The frequencies of calving difficulty and stillbirth in the Norwegian Red population are very low compared to other breeds. Long-term selection has resulted in very low calving difficulty and stillbirths even though these traits have low heritability.


Here are the weights for the calving ease index and the calf stillbirth indexes included in the TMI.


Calving ease traits Relative weight (%) Heritability
Calving ease, paternal  Not included 0.03 
Calving ease, maternal  100 0.02 


Stillbirth traits Relative weight (%) Heritability
Stillbirths, paternal 50 0.01
Stillbirths, maternal  50  0.01

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Storhamargata 44,
N-2317 Hamar, Norway
Phone: +47 950 20 600
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