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Linear Type Evaluations

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 2010 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 2010.

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 2010 represent the genetic base for these averages.

Table 2.
Average STA of Available Bull Population - April 2017 Based on Animal Model Genetic Evaluations
Average STA
Direction   Trait
Average STA
Stature 1.09 Tall   Fore Udder Attachment 1.81 Strong
Strength 0.62 Strong   Rear Udder Height 2.32 High
Body Depth 0.56 Deep   Rear Udder Width 2.13 Wide
Dairy Form 1.00 Open   Udder Cleft 1.01 Strong
Rump Angle 0.06 Sloped   Udder Depth 1.40 Shallow
Rump Width 0.82 Wide   Front Teat Placement 0.83 Close
Rear Legs - Side View 0.22 Curved   Rear Teat Placement 0.79 Close
Rear Legs - Rear View 1.17 Straight   Teat Length 0.29 Short
Foot Angle 1.19 Steep   Udder Composite 1.49 High
Feet & Legs Score 1.26 High   Feet & Legs Composite 1.15 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. This composite index 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:

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

Bulls which have a positive composite index are predicted to have daughters which are, on the average, more desirable for the combination of traits considered in the composite than bulls which have a negative composite index.

Udder Composite Index

The weights on the individual traits comprising the Udder Composite Index were derived from results of a Holstein Association USA research study on herdlife. The herdlife study showed the following weights accurately reflect each udder trait's contribution to increased longevity:

  Udder Depth (UD) .35   Udder Cleft (UC) .09
  Fore Udder Attachment (FU) .16   Front Teat Placement (TP) .05
  Rear Udder Height (UH) .16   Rear Teat Placement (RP) .07
  Rear Udder Width (UW) .12      

Udder Composite is computed as the total of the STAs of these seven udder traits times their respective relative herd life weight (listed above).

UDC = [(UD x .35)+(FU x .16)+(UH x .16)+(UW x .12)+(UC x .09)+(TP x .05 ) - (RP* x .07)]

Feet and Legs Composite

In January 1996, the Holstein Association USA introduced a greatly improved Feet and Legs Composite (FLC). Following extensive research, Holstein Association researchers added two new traits: the linear trait, Rear Legs - Rear View, and the major category, Feet and Legs Score. The new FLC is nearly three times more useful in explaining differences between cows for productive life - for every 1.0 STA increase in FLC you can expect a +0.3 month increase in productive life.

The FLC formula utilizes a 50:50 ratio of the three linear traits combined with the Feet and Legs Score. The three linear traits STAs are weighted:

.48 (Foot Angle) + .37 (Rear Legs - Rear View) - .15 (Rear Legs - Side View)

The overall Feet and Legs Composite is:

FLC = .5 (linear traits) + .5 (Feet and Legs Score)

Feet and legs are a primary concern of dairy farmers throughout the world. A survey recently completed by a leading dairy magazine found the FLC to be one of the five most important traits currently selected by dairy producers in the USA.

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 life. The Feet and Legs Composite combines all four traits into one value that will help Holstein dairy farmers breed longer lasting, more profitable cows.

Body Size Composite Body Size

Body Size Composite is calculated from the linear traits Stature, Strength, Body Depth, Rump Width and Dairy Form. The calculation is:

(.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 40 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).


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