age distribution and generation interval corresponding to four selection pathways of holstein cattle in iran

average age distribution and generation interval were investigated in four different selection pathways. i.e., sire of future sires (ss), sire of future dams (sd), dam of future sires (ds) and dam of future dams (dd). young bulls pathway (yb) is also considered as a path that affects the generation interval in sd pathway when using progeny testing program. data were collected from animal breeding center of iran. data were consisted of 584053 dd, 236628 ds, 345213 sd and 60 ss born from 1994 to 2008. cow survival rates showed a linear diminishing trend (b=-0.0461) with a high r-square (98%) from one lactation to the next. young bulls' sperm usage was much higher than the usage of proved bulls' sperm due to the lower sperm price. this has led to a lower generation interval in ds pathway, when compared with that reported in other studies. on the other hand, percent of usage of local proved sire was very low compared with imported proved sperm. by using age distribution, obtained through different pathways, the generation intervals were recorded as 6.5, 7.5, 4.22, 4.10 and 3.37 years for ss, sd, ds, dd and yb pathways, respectively. considering 20% test capacity, mean generation interval in holstein dairy cattle in iran was around 5.37. to overcome the problem of high generation interval, it is necessary to consider a suitable policy in selection/ culling and in a controlled use of young bulls’ semen.