Records of 4595 lactations from 2254 cows, daughters of 145 sires and 1618 dams of the Gyr breed, assigned to 18 herds, with calving from 1980 to 1997 were used to study the viability of using production from projected partial lactations, on the evaluation of sires. From 91, 151, 211 or 241 days of lactation, 10, 30, 50 or 70% of the lactations were projected, for the duration of the observed lactation and at 305 days of lactation. The estimated of genetic parameters were determined using the MTDFREML system. Independent of the traits, herd-year, season of calving and age of calving with linear and quadratic parameters were included in the models as fixed effects, and considering the animal, permanent environment and error as random effects. Rank and values correlations estimated from the results of genetic evaluations of 145 sires, using estimation production (PE) and P305 ranged from 0.80 to 1.00 (rank correlations) and from .83 to 1.00 (values correlations), respectively. Genetic evaluations using PE were equal by Friedman test to those using P305d. Selecting the best 5% sires based on theirs predicted transmitting ability (PTA) for PE milk yield resulted on the selection of 41.65% to 100% of the same sires as were selected using PTA based on P305. The quadratic log function could be used to extend lactations for sires genetic evaluation; considering the small change in the sires rank. When PEs were used, it is suggested to extend 10% of lactations from 91 days, as the same as to extend 10% to 70% of lactations from 211 days.
genetic evaluation; correlation order and values; partial projected lactation; restricted maximum likelihood; animal model; model animal; Gyr cattle
