The selection index program MTIndex, used by Cottle (2011) to study the sensitivity of genetic gains to variations in genetic parameters, was modified to also allow trait REV (ai) variance.
The breeding objective traits studied were milk yield, fat yield, protein yield, lifespan, mastitis, non-return rate, calving interval and lameness. Mammary composite
score and SCC were included as selection index traits for mastitis, and the feet and leg composite score was the selection index trait for lameness. These are standard traits used by the national genetic evaluation system for dairy cattle in the UK. The sires of dams (SD) pathway was modelled assuming there were 75 progeny records for each bull for the eight selection index traits.
The SD pathway is the most important pathway for commercial dairy producers.