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Linear Type Evaluations
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The linear type trait genetic evaluations incorporate a multi-trait analysis. Multiple trait analysis increases the accuracy of the evaluations by considering the genetic correlations of the given linear trait with all other linear traits.
Genetic evaluations for linear type traits are reported by Holstein Association USA as Standard Transmitting Abilities, or STAs. STAs rank an animal based on its genetic merit relative to the average cow born in 2015 in standard units. Since the bulls being actively marketed by AI organizations have been heavily selected for production and type traits, the AI bull population has a higher STA average for most linear traits compared to cows born in 2015.

Linear type traits can help you breed a more profitable herd of Holsteins through selecting better bulls. Understanding linear type trait STAs can help you:

1. identify the most important traits
2. set realistic genetic goals for each trait
3. select a better group of mating sires
4. mate each cow to a complimentary bull
5. accumulate genetic gains across generations

Table 2 shows the average STAs of bulls coded ACTIVE or LIMITED. Classified cows born in 2015 represent the genetic base for these averages.

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Table 2.
Average STA of Available Bull Population - December 2020 Based on Animal Model Genetic Evaluations
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Average STA
Direction   Trait
Average STA
Stature 0.58 Tall Fore Udder Attachment 1.26 Strong 
Strength 0.15 Strong Rear Udder Height 1.62 High
Body Depth 0.17 Deep Rear Udder Width 1.58 Wide 
Dairy Form 0.79 Open Udder Cleft 0.54 Strong
Rump Angle 0.07 Sloped Udder Depth 0.91 Shallow
Rump Width 0.40 Wide  Front Teat Placement 0.53 Close
Rear Legs - Side View 0.09 Curved  Rear Teat Placement 0.55 Close
Rear Legs - Rear View 0.32 Straight Teat Length 0.35 Long
Foot Angle 0.50 Steep Udder Composite 1.14 High
Feet & Legs Score 0.46 High Feet & Legs Composite 0.32 High


The degree to which a bull or cow is able to genetically influence various characteristics in its offspring is measured by heritability. Faster genetic progress can be achieved for traits which are higher in heritability compared to traits which are lower in heritability. It is difficult to make much genetic progress through selection and mating unless a trait has a heritability of .10 or higher.

Table 3 contains estimates of heritability for linear traits currently summarized by the Holstein Association, USA.

Table 3. Heritabilities of Holstein Association USA type traits.
Trait h2   Trait h2   Trait h2
Stature .42   Rear Legs - Rear View .11   Udder Depth .28
Strength .31   Foot Angle .15   Front Teat Placement .26
Body Depth .37   Feet & Legs Score .17   Rear Teat Placement .32
Dairy Form .29   Fore Attachment .29   Teat Length .26
Rump Angle .33   Rear Udder Height .28   Final Score .29
Rump Width .26   Rear Udder Width .23      
Rear Legs - Side View .21   Udder Cleft .24      

As Table 3 shows, the linear type traits differ substantially in heritability. For example, udder depth has a significantly higher heritability than foot angle. As a result, for a given level of selection, we can expect a greater response in a mating involving udder depth as compared to foot angle. Both the heritability of the trait and the relative economic relationship of the trait to overall profitability should be taken into consideration when determining which traits to incorporate into a breeding program.


Holstein Association USA Linear Composite Indexes combine linear trait information on several related traits into one numerical value. Composite indexes can be used as a selection tool in breeding programs to identify those bulls which are predicted to transmit a desirable combination of the traits in the Composite Index. The traits included in each Composite Index are:

    Udder Depth   Front Teat Placement
    Fore Udder Attachment   Rear Teat Placement
    Udder Cleft   Teat Length
  Rear Udder Height
  Rear Udder Width
  Dairy Form
  Foot Angle
  Feet & Legs Score
  Rear Legs - Side View
  Rear Legs - Rear View
  Rump Width
    Body Depth  Dairy Form

Udder Composite and Feet & Legs Composite were developed to increase individual lactation averages, productive life, and lifetime production of fat and protein. A negative weight on stature results in the decoupling of the composites from stature, allowing breeders to improve udders and feet & legs without making their cows taller.

Udder Composite Index

Udder Composite describes a well formed capacious udder with strong attachment. Using bulls with a high UDC results in a lowering of the somatic cell score and daughters whose udders are trouble-free and capable of holding more milk.


The UDC formula is as follows:

UDC = [(.16 x FU) + (.23 x UH) + (.19 x UW) + (.08 x UC) + (.20 x UD) +
(.04 x TP) + (.05 x RP*) + (.05 x TL*) - (.2 x ST)] x 1.16

RP* and TL* have an intermediate optimum. There is a penalty for rear teats that are placed too close to one another. The same goes for teat length. Teats that too long or too short are penalized.
The value 1.16 is used to standardize the composite with the 2015 Base Population of cows.

FU = Fore Udder Attachment
UC = Udder Cleft
RP* = Rear Teat Placement
UH = Rear Udder Height
UD = Udder Depth
TL** = Teat Length
UW = Rear Udder Width
TP = Front Teat Placement
ST = Stature

* If Rear Teat Position is less than or equal to 1, then RP* = RP.
If Rear Teat Position is greater 1, then RP* = 1-(RP x 0.1).

**TL* = (-1 x ABS(TL)) - (ABS(TL) x ABS(TL) x 0.1) where ABS(TL) is the absolute value of Teat Length

The desirability curves for Rear Teat Placement and Teat Length are shown below:

Feet & Legs Composite Index

The Feet & Legs Composite formula utilizes a combination of the major category Feet & Legs Score along with three linear traits. The FLC formula is as follows:

FLC = [(.05 x FA) + (.20 x RV) + (.05 x SV*)+ (.70 x FLS) - (.20 x ST)] x 1.14
*Where SV (Rear Legs - Side View) has an intermediate optimum

The value 1.14 is used to standardize the composite with the 2015 Base Population of cows.

FA = Foot Angle     RV = Rear Legs Rear View     FLS = Feet & Legs Score     ST = Stature     SV* = Rear Legs Side View

SV* = (-0.27 x ABS(SV)) - (ABS(SV) x ABS(SV) x 0.22)
where ABS(SV) is the absolute value of Rear Legs - Side View

Feet and legs are a primary concern for dairy producers worldwide. Selecting animals that transmit superior mobility, steeper foot angle, wider rear leg stance with little or no hock-in and slightly straight rear legs (side view) will result in animals capable of longer productive lives. The Feet and Legs Composite was designed to maximize within-herd lifetime production of combined Fat and Protein.


Body Weight Composite Index

The Body Weight Composite includes a measure of both body size, i.e., the dimensions of the cow, and dairy form. By including dairy form, we take into consideration how hard the cow is milking, accounting for an excess or lack of body fat. The BWC formula is as follows:

BWC = (.23 x Stature) + (.72 x Strength) + (.08 x Body Depth) + (.17 X Rump Width) - (.47 x Dairy Form)

Every 1.0 STA increase in body size correlates with a 35 pound predicted increase in mature body weight. For example, daughters of bulls that sire large cows (large positive evaluations for body size, +3.00) are predicted to weigh 240 pounds more than those that sire small cows (large negative evaluations for body size, -3.00.)