FOUR-GENERATION BREED STACKS

1

• 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.

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 (n246,218)
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.
Table 1. Number of animals with a non-zero
breed fraction for each major breed.
Table 2. Number of F1s for each major breed cross.
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 --------------------------
---------------------------------- HOGUHOHOGUGUHO
HOHOHOGUGUGUGUHOHOHOHOHOHOHOHOGUGUGUGUGUGUGUGU In
this example, the sire and the dam are purebred
animals for the previous four generations.