Selection indexes have been extensively applied in the estimation of breeding value of dairy cattle for single traits as well as for combinations of traits for selection purposes. Milestones in methodology, such as multiple-trait evaluation procedures by BLUP, (co)variance component estimation, nonlinear models, discounted gene flow, dynamic programming, and international sire evaluations, together with increased computing power and the development of integrated AI and recording schemes, have contributed to efficient implementation of selection indexes and are reviewed in this article. Results of an international survey on evaluation practices and breeding programs are presented, demonstrating wide adoption of index selection for total merit and the need for further applications. Results from a simulation study on the efficiency of index selection for total merit are also presented; when the breeding goal includes, in addition to production traits, functional nonproduction traits such as mastitis resistance and fertility, failure to consider these traits in the selection index decreases efficiency 15 to 25%. Future applications are also discussed in view of advances in the areas of genome mapping, marker detection, and international comparisons. Further research should focus on functional nonproduction traits.

Summary Data from a Boran cattle breeding scheme, run by the Ministry of Agriculture in Ethiopia, were analysed by separating the genetic and environmental trends in growth traits. The data used included weight records at birth (BW), weaning (WW), and as yearlings (YW), for animals born between 1959 and 1985. The mean generation interval calculated was 6.75 years. In a 24‐year actual selection period, 3.29 generations of selection occurred, during this time inbreeding increased, to an average of 1.7% in animals born in 1985. The regressions of estimated direct and maternal breeding value on year of birth were −0.002 and 0.003 kg, 0.32 and 0.02 kg, and 0.22 and −0.005 kg, for BW, WW, and YW respectively. The aggregate breeding value, which is the sum of the maternal and direct breeding values, showed an increase of 0.34 and 0.21 kg per year for WW and YW, respectively. Whereas the maternal environmental trends were slight, the variation in the direct environmental effects was the greatest. Generally, a less marked annual genetic trend was shown, when breeding values were regressed on generation coefficients than on year of birth. Despite the good opportunity for selection, that was demonstrated by the more than 50 kg difference between the maximum and minimum breeding values for WW and YW, the maximum genetic gain in aggregate breeding value was only 0.2% of the mean WW per year. This limited response was due to the high level of genetic antagonism between direct and maternal effects, and also to problems in running the selection scheme, for example, selection on phenotypic performance alone and relatively long generation intervals. Zusammenfassung Genetische und umweltbedingte Trends von Wachstumseigenschaften bei Boran Rindern Die Daten des Boran Zuchtprojektes des äthiopischen Landwirtschafsministeriums wurden zur Trennung genetischer und umweltbedingter Trends analysiert, und zwar Geburts‐ (BW), Absatz‐ (WW) und Jährlingsgewicht (YW) der zwischen 1959 und 1985 geborenen Tiere. Das mittlere Generationsintervall war 6,75 Jahre, so daß in der 24 Jahresperiode 3,29 Generationen abgelaufen sind, während welchen der Inzuchtgrad auf 1,7% bei den 1985 geborenen Tieren angestiegen ist. Regression geschätzter direkter und maternaler Zuchtwerte auf Geburtsjahr waren −0,002 und 0,003 kg für BW, 0,32 und 0,02 für WW ond 0,22 und −0,005 kg für YW. Die Summe beider Zuchtwerte, aggregierter Zuchtwert, ist damit um 0,34 und 0,21 kg für WW und YW angestiegen. Der Umwelttrend für maternale Wirkungen war gering, der für direkte zeigte große Variabilität. Der jährliche genetische Trend war geringer, wenn die Regression auf Generation statt Geburtsjahr bezogen wurde. Trotz guter Selektionsmöglichkeit, wie sie durch die mehr als 50 kg weite Spanne zwischen höchsten und neidrigsten Zuchtwerten für WW und YW deutlich wird, war der maximale Zuchtforschritt im Gesamtzuchtwert nur 0,2 % des jährlichen WW Durchschnittes. Dieser begrenzte Erfolg ist auf genetischen Antagonismus zwischen direkten und maternalen Wirkungen zurückzuführen, abe...