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Total Merit Index

Total Merit Index

Since 1978, TMI (Total Merit Index) has been used to identify the best Norwegian Red bulls to become elite, daughter-proven sires throughout Norway.

Uniquely and in contrast to most other dairy breeds, simultaneous genetic improvement for production, fertility and health traits was realized by heavily weighting these traits in TMI.


Starting in 2016, the highest ranking genomic selected (GS) Norwegian Red bulls, based on their TMI, are selected and used as elite sires in Norway and internationally. However, this transition to 100% genomic selection using the HD Genomics platform was implemented after many years of rigorous testing:1) starting in 2011 information from genotyped animals was used in pre-selection of sires, 2) multi-year development of a single-step genomic evaluation method to calculate breeding values and 3) inclusion of many more genotyped animals (including females) prior to and since 2016. As long as some export markets request daughter-proven bulls, a number of GS bulls will be retained to become daughter-proven bulls.

 

Thirteen traits or trait groupings (indexes) are included in the current TMI (Table 1) with production, udder health, udder conformation and fertility indexes receiving the highest relative weights within the TMI. The relative weight factors in our TMI will secure a maximal genetic response for all traits, and the importance of these key traits in the breeding goal will continue to have positive genetic trend with our newly implemented HD-Genomics in Norway.

 

Table 1: Relative weights on individual traits included in the TMI.

Traits Relative weight (%)*
Production index 24
Udder conformation index 23
Udder health index 16
Daugther fertility index 14
Beef index (males)  7
Claw health index 4
Foot and leg conformation 2.2
Calving ease index 1.7
Rump angle index 3.7
Stillbirth index 1.4
Milking speed 3.8
Leakage 0.5
Other diseases resistance index 0.4
Temperament 0.4

 *The relative weight (%) is the percentage of emphasis put on a trait in the group of traits in TMI

Production index (24% of TMI)

The production index is based on data collected by the Norwegian Dairy Herd Recording System. 

 

The production index includes several yield traits.

 

Trait Relative weight (%)
Kg milk  5
Kg fat 47.5
Kg protein 47.5
Protein (%) Not included
Fat (%) Not included

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

Udder conformation index (23% of TMI)

The udder conformation index consists of nine traits viewed from the exterior of the cow. These udder traits are weighted in such a way that a high score for udder index reflects a durable and functional udder.

 

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

 

The udder conformation index consists of nine traits with weights as indicated here.

 

Trait Relative weight (%)
Udder depth 21
Front teat placement 12.3
Rear teat placement 12.4
Udder balance 6
Fore udder attachment 14.7
Rear udder width 3.6
Rear udder height 7.5
Udder cleft 13.3
Teat length 9.4

Udder health index (16% of TMI)

Resistance to  clinical mastitis has been included in the TMI since 1978 with gradually increasing emphasis. Udder health (mastitis) causes the greatest economic losses of any disease in dairy cattle. The Norwegian Red now has a low frequency of clinical mastitis (CM) due in part to genetic progress in resistance to mastitis. 

 

Veterinary treatments are recorded for acute clinical or chronic clinical mastitis in periods of 1st, 2nd and 3rd lactations. 0 = no treatments recorded, 1 = one or more treatments recorded.

 

SCC is the 305-day lactation geometric mean of SCC.

 

Somatic cell count (SCC) and CM are highly correlated genetically, meaning that selection for SCC (the trait with higher heritability) will result in indirect selection for CM (each are influenced by some of the same genes). A low incidence of clinical mastitis makes it important to include SCC from an economic standpoint and, also, for indirect selection to continue to improve clinical mastitis resistance. 

 

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

 

Trait  Relative weight (%)
Somatic cell count 68
Clinical mastitis 32

Daughter fertility index (14% of TMI)

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 sustainded selection for increased fertility for over 40 years. 

 

The fertility index was recently improved by replacing non-return rate with number of inseminations. Number of inseminations is biologically very similar to non-return rate, but it has more genetic variation since cows requiring more inseminations are penalized more heavily than cows with just one unsuccessful insemination.

 

The daughter 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

 

Beef index (males) (7% of TMI)

The beef index is made up of three traits that are measured on bulls fed for beef.

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

 

Trait Relative weight (%)

Slaughter weight (growth rate)

60

Slaughter classification (EUROP scoring)

20

Fat grading

20

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

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

Claw disorders related to laminitis 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.

 

Trait Relative weight %
Corkscrew claw 50
Infectious claw disorders 30
Laminitis related claw disorders 20

Foot and leg conformation index (2.2% of TMI)

Breeding advisors record foot and leg conformation traits together with other conformation traits. These 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.

 

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

Calving ease index (1.7% of TMI) 

The frequency of calving difficulty in the Norwegian Red population are very low compared to other breeds. Paternal calving ease (calving ease attributed to sire of calf) was recently added to maternal calving ease (how daughters of a bull perform when they calve) to make up the calving ease index.


Long-term selection for calving ease since 1978 has resulted in a low frequency in calving difficulty even though the two calving ease traits have low heritability. NOTE: See discussion in rump angle (below) as this trait adds to the accuracy of selection for maternal calving ease.


Here are the weights for the two traits included in the calving ease index.

 

Calving ease traits Relative weight (%)
Calving ease, paternal  50
Calving ease, maternal 50

 

Rump angle index (3.7% of TMI)

Rump angle is an important trait related to calving difficulties. With the move to GS, maternal calving ease has a lower reliability compared to reliability under the progeny test program. The indirect information on rump angle in TMI now adds significantly to the accuracy for selection to improve maternal calving ease. 

Stillbirth index (1.4% of TMI)

The frequency of stillbirths in the Norwegian Red population are very low compared to other breeds. Paternal stillbirths are those attributed to the sire of calf and maternal stillbirths are those attributed to the daughters of a bull.

 

Long-term selection for decreasing stillbirths since 1978 has resulted in very low frequency of stillbirths even though the two stillbirth traits have low heritability.


Here are the weights for the two traits included in stillbirth index.

 

Stillbirth traits Relative weight (%)

Stillbirths, paternal

(also called direct or service sire)

50
Stillbirths, maternal  50 

 

Milking speed index (3.8% of TMI)

Milking speed has an important economic impact on herd profitability and its importance has increased in herds with automatic milking systems, which have become widespread in Norway.

 

Milking speed is scored by farmers on first-lactation heifers. They use a scale of 1 to 3, where 1=Fast, 2=average and 3=slow. The new TMI of June 2017 has added milking speed to address the importance of milking speed as well as its impact on leakage and mastitis. 

Leakage index (0.5% of TMI)

Leakage is dripping or flowing of milk between milkings. This trait is subjectively scored by farmers on first-lactation heifers. They use a scale of 1 to 3, where 1=none, 2=a little and 3=obvious.

 

A strong correlation exists between leakage and milking speed. Before changes in TMI in June 2017, leakage was improving, but milking speed was starting to decline slightly. To stabilize the response and avoid reduction in milking speed, milking speed was given a 3.8% of the weight in TMI and the weight on leakage was increased to 0.5%.

Diseases other than mastitis index (0.4% of TMI)

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.

 

Veterinary treatments were recorded for ketosis, milk fever or retained placenta between 15 days pre-partum and 120 days post-partum. In addition, treatments were recorded for the fertility disorders: Cystic ovaries, metritis and silent heat. 0=no treatments recorded, 1=one or more treatments recorded. Data is recorded from cows in 1st to 5th lactations.

 

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:

 

Trait Relative weight (%)
Ketosis 45
Milk fever 15
Retained placenta 15
Cystic ovaries 15
Metritis 5
Silent heat 5

Temperament index (0.4% of TMI)

This trait is scored by farmers on first-lactation heifers and is reported to the Norwegian Dairy Herd Recording System. They use a scale of 1 to 3, where 1 is easy, 2 is average and 3 is uneasy. 


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Storhamargata 44,
N-2317 Hamar, Norway
Phone: +47 950 20 600
E-mail: post@geno.no
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