Since February 1998, genetic evaluations for 15 linear type traits have been generated by a new multi-trait animal model. The American Jersey Cattle Association Board of Directors approved this action in order to take advantage of advanced technology that results in 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 progeny information and maternal and paternal pedigree information. The result is an estimate of 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 are generated using animal model methodology.

In contrast to the sire model used previously, an animal model uses information from the maternal side of the pedigree. In the sire model the only maternal contribution was through the maternal grandsire. 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 combining the genetic relationships between all linear traits. The multi-trait animal model produces simultaneous solutions for all linear type traits.

The multi-trait animal model was applied to Jerseys by Dr. Nicolas Gengler, Gembloux, Belgium, in part through financial support of the AJCC Research Foundation. Dr. George Wiggans and Jan Wright of the U.S. Department of Agriculture-Animal Improvement Programs Laboratory (USDA-AIPL) have been instrumental with the implementation of the new technology.

New genetic parameters and age adjustment factors have been developed for use with the animal model. In addition, the new system requires an appraisal of the first lactation for the genetic evaluation. Appraisal information obtained in third and later lactations are not included in the genetic evaluations. Beyond second lactation, appraisal information is more heavily influenced by non-genetic factors such as preferential treatment of individual cows and varied culling practices. However, the appraisal program is not affected by the change in the statistical model. All appraisal scores continue to appear in performance documents.

Heritability estimates increase by an average of 0.02 over estimates used by USDA with the sire model (Table 1). Heritability estimates tell us how much actual appraisal scores reflect genetic differences between animals. As the heritability estimate increases, more of the resulting Predicted Transmitting Ability (PTA) is based on the appraisal score. The greatest increases in heritabilities are in:

• Udder Depth (from .27 to .38)

• Rear Udder Height (from .17 to .26)

• Dairy Form (from .16 to .23)

• Rear Udder Width (from .17 to .23)

• Front Teat Placement (from .18 to .24)

Table 1. Heritability Estimates For Type Traits

Trait	Animal Model	Sire Model	Difference
Stature	0.39	0.40	-0.01
Strength	0.25	0.24	0.01
Dairy Form	0.23	0.16	0.07
Foot Angle	0.10	0.12	-0.02
Rear Leg	0.10	0.12	-0.02
Rump Angle	0.31	0.27	0.04
Thurl Width	0.20	0.24	-0.04
Fore Udder Attachment	0.22	0.18	0.04
Rear Udder Height	0.26	0.17	0.09
Rear Udder Width	0.23	0.17	0.06
Udder Depth	0.38	0.27	0.11
Udder Cleft	0.20	0.16	0.04
Teat Placement	0.24	0.18	0.06
Teat Length	0.26	0.26	0.00
Final Score	0.23	0.23	0.00
Average			0.021

It is helpful to know how the new genetic evaluations compare with the previous information. To provide this comparison, the appraisal information used to generate the August 1997 genetic evaluations was used to produce similar information using the new multi-trait system. The data included bulls with 20 or more daughters in their August 1997 type proof.

The results of the comparison indicate that we can expect some re-ranking of bulls and cows. The correlations between the two systems are generally high but not perfect. The primary reasons for differences between the PTAs from the two models are:

• the direct accounting for merit of sire and dam in contrast to the sire model where groups were assigned based on sire and maternal grandsire evaluations for final score;

• the requirement for an appraisal in first lactation, and the fact that appraisals after second lactation are not used in genetic evaluations;

• the new variance components and age adjustments, and

• the new model which allows data from each trait to affect evaluations of all other traits.

Correlations between the PTAs for linear traits comparing the sire model with the multi-trait model appear in Table 2. Generally, the correlations are high ranging from a low of 0.77 for Udder Cleft to a high of 0.91 for Foot Angle and Strength. Correlations between the genetic estimates increase over time as younger bulls are more similar between the two methods. Correlations increase for bulls with more than 40 progeny.

Table 2. Correlation Between Type PTAs from Sire and Multi-Trait Models

Trait	PTAs
Stature	0.90
Strength	0.91
Dairy Form	0.85
Foot Angle	0.91
Rear Leg	0.80
Rump Angle	0.80
Thurl Width	0.89
Fore Udder Attachment	0.86
Rear Udder Height	0.84
Rear Udder Width	0.89
Udder Depth	0.89
Udder Cleft	0.77
Teat Placement	0.86
Teat Length	0.88
Average	0.858

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 genetic evaluation model that was started in February of 1998 will continue to bring more accurate type information and provide Jersey breeders a greater opportunity for breed improvement.