Repeatability of auxiliary sire indices with different progeny group size

The repeatability of auxiliary sire indices was examined using first lactat ion data of Holstein-Friesian crossbred cows. Age at first calving (AFC), f irst service period (FSP), first lactation length (FLL), first dry period ( FDP) and first calving interval (FCI) were used as auxiliary traits in the present study. There was 5.26% increase in accuracy of sire evaluation when FLL, was used as auxiliary trait, for other auxiliary traits the gain was very less. Similarly, number of daughters' records required for a pre-assig ned level of accuracy was also less in case of FLL as auxiliary trait. The repeatability of breeding value estimates was obtained by determining the c orrelation of the breeding value of sires' estimate based on 5, 8 and 12 da ughters with that of 'true' breeding value (based on 15 or more daughters r ecord). The repeatability of auxiliary sire evaluation was higher when prog eny group size per sire was small ranging from 5 to 8. With the increase of daughter number there was no advantage of incorporation of auxiliary trait s over sire evaluation based on milk yield record of daughters.