International dairy sire evaluations have traditionally been calculated usi
ng a two-step process. Lactation records within each country are used to pr
edict national estimated breeding values, then these national breeding valu
es are transformed to the genetic base, scale, and units of measurement of
other countries by using conversion formulae or the multiple-trait, across-
country evaluation method. A major limitation of this approach is the need
to define environments (traits) according to country borders. Herds located
in small, neighboring countries may be much more similar in management, cl
imate, and genetic background than herds located far apart within a single
large country. In the present study, international genetic evaluation with
herd clusters is proposed. Data consisted of 4.6 million lactation records
from 46,000 herds in Austria, Belgium, Czech Republic, Denmark, Estonia, Fi
nland, Israel, Switzerland, and five regions of the US (Midwest, Northeast,
Northwest, Southeast, and Southwest). Herds were grouped into clusters bas
ed on data of 13 descriptive variables: herd size, calving interval, milkin
g frequency, age at first calving, milk yield, month of calving, predicted
transmitting ability of sire for milk, percentage North American genes of s
ire, latitude, altitude, temperature, rainfall, and percentage of arable la
nd used for pasture. Five clusters were formed; each cluster contained herd
s from 5 to 11 countries or regions. Genetic correlations between herd clus
ters ranged from 0.81 to 0.97. The herd cluster model is intuitively appeal
ing, because genetic merit of an animal is predicted for each unique enviro
nment or management system, regardless of country borders. This model is pa
rsimonious (the number of traits was reduced from 13 to 5) and is computati
onally feasible for large data sets.