GENETIC EVALUATIONS FOR TYPE FOR BREEDS OTHER THAN HOLSTEIN
N. Gengler, G.R. Wiggans, C.W. Wolfe, and J.R. Wright
Beginning in February 1998, evaluations for the 15 linear type traits are now calculated with a multi-trait animal model which takes advantage of advanced technology to provide more accurate information for breed improvement.
Animal model refers to a system of cow and bull evaluations in which the genetic merit of all relatives plus the animal's own performance are used to estimate the animal's genetic merit. The animal's own appraisal information is combined with information from progeny, sire, and dam to estimate the animal's transmitting ability for type traits. Genetic evaluations for production traits such as milk, fat, and protein as well as the fitness traits, somatic cell score, and productive life also are generated using animal model methodology.
In contrast to the sire model previously used for bulls, an animal model uses information from the maternal side of the pedigree. Genetic evaluations generated by the animal model are more accurate because additional information is used in the calculations.
A multi-trait animal model provides an even greater increase in accuracy by using the genetic relationships among all linear traits. The multi-trait animal model produces simultaneous solutions for all linear type traits, even if a type trait is missing for a given cow. Programs to implement the multi-trait animal model were developed by Dr. Nicolas Gengler, Gembloux, Belgium, in part through financial support from the American Jersey Cattle Association (AJCA), the Ayrshire Breeders Association (ABA) and the American Guernsey Association (AGA).
New genetic parameters and age adjustments were developed for use with the animal model. In addition, to avoid selection bias, the new system requires an appraisal in the first lactation except for the Brown Swiss and Milking Shorthorn breeds. For these breeds an appraisal in first or second lactation is required because there sometimes is an 18 month interval between appraisals. Lactation number is validated by considering age at calving. There is also an upper limit on age at appraisal which varies by breed. (Table 1). These limits prevent using data after the maximum age of mandatory scoring. Selection bias occurs when a bull could be represented by only selected daughters. If all a bull's poor daughters are culled before any daughters are scored, his evaluation would be higher than his true genetic value. Similarly, with cows beyond the age of maximum scoring, only the cows likely to have their scores improved are scored thus giving them too high a genetic estimate.
Table 1. Upper age limits on appraisal information included in type evaluations
| Breed | Limit |
| Ayrshire | 60 months of age |
| Brown Swiss | 68 months of age |
| Guernsey | Before June 1997, first or second lactation appraisal only. Now, lactations 1 through 3 |
| Jersey | First or second lactation appraisal only |
| Milking Shorthorn | 68 month of age |
| Red and White | 77 months of age |
Heritability estimates tell us how much actual appraisal scores reflect genetic differences between animals. With higher heritability estimates, more of the resulting Predicted Transmitting Ability (PTA) is based on the cows own appraisal. Heritability estimates generally increased for Ayrshire, Guernsey , Jersey, and Red and White by an average of 0.02 to 0.07 over estimates used with the sire model (Table 2). For Red and White, Holstein estimates are used. Heritability estimates decreased on the average for Brown Swiss and Milking Shorthorn (-0.03 to -0.04), indicating they may have been slightly too high with the sire model.
Table 2. Heritability estimates for type traits
| SireMod | Ayr | BSw | Gue | Jer | MSh | R&W | |
| Final Score | *see note | 0.26 | 0.27 | 0.26 | 0.23 | 0.28 | 0.26 |
| Stature | 0.40 | 0.45 | 0.39 | 0.48 | 0.39 | 0.41 | 0.41 |
| Strength | 0.24 | 0.31 | 0.21 | 0.30 | 0.25 | 0.26 | 0.30 |
| Dairy Form | 0.16 | 0.24 | 0.18 | 0.34 | 0.23 | 0.18 | 0.28 |
| Foot Angle | 0.12 | 0.11 | 0.08 | 0.11 | 0.10 | 0.09 | 0.14 |
| Rear Leg | 0.12 | 0.10 | 0.14 | 0.18 | 0.10 | 0.09 | 0.21 |
| Body Depth | 0.34 | 0.38 | 0.23 | 0.33 | 0.25 | 0.30 | 0.37 |
| Rump Angle | 0.27 | 0.30 | 0.24 | 0.40 | 0.31 | 0.19 | 0.33 |
| Thurl Width | 0.24 | 0.29 | 0.13 | 0.30 | 0.20 | 0.16 | 0.26 |
| Fore Udder Attachment | 0.18 | 0.26 | 0.16 | 0.23 | 0.22 | 0.11 | 0.29 |
| Rear Udder Height | 0.17 | 0.29 | 0.19 | 0.32 | 0.26 | 0.13 | 0.27 |
| Rear Udder Width | 0.17 | 0.23 | 0.15 | 0.32 | 0.23 | 0.12 | 0.23 |
| Udder Depth | 0.27 | 0.25 | 0.24 | 0.38 | 0.38 | 0.27 | 0.28 |
| Udder Cleft | 0.16 | 0.25 | 0.13 | 0.18 | 0.20 | 0.05 | 0.24 |
| Teat Placement | 0.18 | 0.25 | 0.18 | 0.27 | 0.24 | 0.18 | 0.26 |
| Teat Length | 0.26 | 0.29 | 0.26 | 0.30 | 0.26 | 0.24 | |
|
Average change in h2 |
0.04 | -0.03 | 0.07 | 0.02 | -0.04 | 0.06 |
note: Sire model heritabilities were the same for linear traits; unique for final score. For final score they were: Ayrshire = 0.30, Brown Swiss = 0.37, Guernsey = 0.30, Jersey = 0.23, Milking Shorthorn = 0.30, Red & White = 0.23.
To determine how the new genetic evaluations compare with evaluations from the previous system, evaluations released in August were compared to those calculated for the February 1998 release using the new system. The results of the comparison indicate some re-ranking of bulls and cows. The correlations between the two systems are moderately high but many are below 0.9 which indicates a significant effect of the new model and parameters. Correlations between the PTAs for linear traits comparing the sire model with the multi-trait animal model appear in Table 3. The average correlation by breed ranged from a low of 0.75 for Milking Shorthorn to a high of 0.88 for Guernsey.
Table 3. Correlations between type PTAs from August 1997 sire model and February 1998 multi-trait animal model for bulls with at least 20 daughters, born 1975 or later:
| Ayr | BSw | Gue | Jer | MSh | R&W | |
| Final Score | 0.84 | 0.86 | 0.90 | 0.90 | 0.82 | 0.77 |
| Stature | 0.90 | 0.85 | 0.94 | 0.90 | 0.88 | 0.86 |
| Strength | 0.81 | 0.72 | 0.92 | 0.84 | 0.77 | 0.83 |
| Dairy Form | 0.65 | 0.74 | 0.91 | 0.90 | 0.72 | 0.85 |
| Foot Angle | 0.76 | 0.71 | 0.84 | 0.78 | 0.69 | 0.85 |
| Rear Leg | 0.76 | 0.83 | 0.86 | 0.81 | 0.76 | 0.85 |
| Body Depth | 0.82 | 0.79 | ||||
| Rump Angle | 0.88 | 0.86 | 0.93 | 0.87 | 0.74 | 0.93 |
| Thurl Width | 0.83 | 0.66 | 0.93 | 0.85 | 0.70 | |
| Fore Udder Attachment | 0.85 | 0.82 | 0.79 | 0.84 | 0.64 | 0.83 |
| Rear Udder Height | 0.82 | 0.85 | 0.89 | 0.87 | 0.80 | 0.81 |
| Rear Udder Width | 0.78 | 0.73 | 0.89 | 0.87 | 0.65 | 0.83 |
| Udder Depth | 0.71 | 0.63 | 0.83 | 0.77 | 0.81 | 0.81 |
| Udder Cleft | 0.82 | 0.83 | 0.87 | 0.85 | 0.67 | 0.78 |
| Teat Placement | 0.86 | 0.88 | 0.90 | 0.87 | 0.78 | 0.86 |
| Teat Length | 0.89 | 0.85 | ||||
|
Average |
0.805 | 0.784 | 0.882 | 0.848 | 0.745 | 0.835 |
The PTA's of artificial insemination (AI) bulls active following the August run were examined to determine the differences in means for final score. These differences and differences in standard deviations (SD) for all bulls with evaluations in both runs are in Table 4. The PTA for final score increased for this specific group of bulls from an average of 0.07 for Guernsey to 0.73 for Jersey. Standard deviations increased for all breeds except for Ayrshire. An increase in SD could cause the mean of a selected group of bulls to increase even when the mean for all bulls was nearly the same. The base population was again the cows born in 1990 and their PTA's average 0 for each trait.
Table 4. Difference in mean for active AI bulls and standard deviation for all bulls with evaluations between August 97 sire model and February 98 multi-trait animal model for PTA final score.
| Breed | Difference in mean | Difference in SD |
| Ayrshire | 0.33 | -0.05 |
| Brown Swiss | 0.27 | 0.02 |
| Guernsey | 0.07 | 0.01 |
| Jersey | 0.73 | 0.02 |
| Milking Shorthorn | 0.20 | 0.06 |
| Red and White | 0.57 | 0.03 |
The primary reasons for differences between the PTAs from the two models are:
1) the direct accounting for merit of sire and dam in contrast to the sire model where groups were assigned based on sire and maternal grand sire evaluations for final score; 2) the requirement for an appraisal in first lactation in some breeds, and some later appraisals are not used in genetic evaluations; 3) the new variance components and age adjustments; 4) the multi trait model which allows data from each trait to affect evaluations of all other traits, and 5) the additional six months of data included and exclusion of final score data before 1980.
Correlations between the genetic estimates increase with birth year of the bull so younger bulls are more similar between the two methods. Correlations also were higher for bulls with more progeny. Cows and bulls are evaluated simultaneously with the multi-trait animal model. As a result, cows are more accurately evaluated as compared to separate evaluations for cows and bulls with the sire model.
Type evaluations will be available four times a year, coinciding with production evaluations. The February 1998 genetic evaluations bring more accurate type information and provide breeders a greater opportunity for breed improvement.
***Portions of this article were adapted from the article New Genetic Evaluations for Type by C.W. Wolfe. Jersey Journal. January 1998.***
***N. Gengler is Chargé de Recherches of the Fonds National Belge de la Recherche Scientifique (FNRS).***