Crossbreds are animals whose genes are derived from more than one breed, such as a cow with a Holstein sire and a Jersey dam. A system for storing breed composition data for US dairy cattle has been developed and the necessary software implemented. This system is necessary to facilitate implementation of an across-breed genetic evaluation. Crossbred animals in the US dairy cattle population do not currently receive genetic evaluations. Two ways that crossbred animals may be handled in an evaluation are: they may be included in the breed-of-sire evaluation, or all animals may be combined into a single evaluation. For each crossbred cow (n=246,218) the database stores animal identification, breed of animal registry, breed fractions for 18 dairy breeds and an “unknown” category, a four-generation breed stack, a sire breed stack, and a heterosis value. Standard two-letter breed codes are used in the breed stacks. Breed fractions were calculated from pedigree information in the USDA database as far back as data were available.

1. Breed Composition Codes for Crossbred Dairy Cattle in the United States
Jo hn B. Co le , * Me lvin E. To o ke r, PaulM. VanRade n, and Jo e lH. Me g o nig al, Jr.
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350.
FOUR-GENERATION BREED STACKS
The four-generation breed stack is a text string describing an animal's
breed composition for the four most recent generations. This allows for the easy
identification of rotational crossbreeding systems. The breed stack for a HO x
GU F1 cow is:
Breed Composition
------------------------------------------------------------
HOGUHOHOGUGUHOHOHOHOGUGUGUGUHOHOHOHOHOHOHOHOGUGUGUGUGUGUGUGU
In this example, the sire and the dam are purebred animals for the previous four
generations.
INTRODUCTION
Crossbreds are animals whose genes are derived from more than one
breed, such as a cow with a Holstein sire and a Jersey dam. A system for
storing breed composition data for US dairy cattle has been developed and the
necessary software implemented. This system is necessary to facilitate
implementation of an across-breed genetic evaluation. Crossbred animals in the
US dairy cattle population do not currently receive genetic evaluations. Two
ways that crossbred animals may be handled in an evaluation are: they may be
included in the breed-of-sire evaluation, or all animals may be combined into a
single evaluation. For each crossbred cow (n=246,218) the database stores
animal identification, breed of animal registry, breed fractions for 18 dairy breeds
and an “unknown” category, a four-generation breed stack, a sire breed stack,
and a heterosis value. Standard two-letter breed codes are used in the breed
stacks. Breed fractions were calculated from pedigree information in the USDA
database as far back as data were available.
SUMMARY STATISTICS
There are currently 246,218 crossbred animals stored in the AIPL
database. Results are presented for the six major dairy breeds in the US:
Ayrshire (AY), Brown Swiss (BS), Guernsey (GU), Holstein (HO), Jersey (JE),
Milking Shorthorn (MS). The number of animals in the table with non-zero breed
fractions are presented in Table 1. The number of F1 animals for each of the six
major breeds are presented in Table 2.
SIRE BREED STACKS
The sire breed stack is a summary of the breed of sire and sires of the
maternal line as far back as pedigree data are available. The sire breed stack
for the HO x GU F1 from the previous example is:
Sire Breed Stack
------------------------------------------------------------
HOGUGUGUGU
Due to the absence of breed information about paternal ancestors, rotational
crossbreeding systems cannot be identified from the sire breed stack. However,
when purebred sires are used this information provides a complete description of
the mating system being used.
GENETIC EVALUATION OF CROSSBREDS
There are three basic approaches to using records from crossbred animals
in a genetic evaluation program:
• Do not use the records (the current system).
• Use the crossbred animals in the breed-of-sire evaluation.
• Use records from all animals in a single across-breed evaluation.
The current system, under which crossbred records are not used, is the least
desirable option because it discards information in the form of records. The third
option is the most technically challenging but appealing option. The second
option is not as satisfying as the third, but it is the simplest to implement.
CONCLUSION
There is now a system in place for easily identifying crossbred dairy cattle in
the United States, and research into methods for genetic evaluation of these
animals is ongoing.
Table 2. Number of F1s for each major breed cross.
Table 1. Number of animals with a non-zero breed
fraction for each major breed.
AY BS GU HO JE MS
0
20000
40000
60000
80000
100000
120000
140000
160000
11234
27030 29331
148539
50278
5571
Breed
NumberofAnimals
Breed AY BS GU HO JE MS
AY 8,200 543 420 6,227 543 206
BS 17,973 676 15,257 1,321 106
GU 15,711 13,089 1,230 155
HO 68,382 28,969 3,300
JE 32,404 175
MS 4,102