Selection for yearling weight has been applied in two (120-cow, 6-sire) purebred herds from Nelore (NeS) and Guzera (GuS) breeds of Zebu cattle since 1980. A Nelore control (NeC) herd (60-cow, 4-sire) has been used to evaluate the genetic change. Selection criteria were the bull's weight at 378 d (W378) and heifer's weight at 550 d (W550). Average age of parents were 4.79; 4.72 and 4.75 yr for NeS, NeC and GuS, respectively. For calves born in 1985,the midparent cumulative selection differentials in standard units were 1.863 in NeS; 1.335 in GuS and .258 in NeC. Data recorded on 629 progeny were used to evaluate the selection response. The yearly deviations NeS-NeC in W378 were 14.0; 18.3; 17.3 and 14.7 kg for males born from 1981 to 1984, respectively. Corresponding values for GuS-NeC were 0.0; 17.1; 6.7 and 10.4 kg. In the females,the early deviations NeS-NeC in the W550 were 17.8; -.7 and 10.5 kg for the years 1981 to 1983, respectively. Corresponding values for GuS-NeC were -2.4; -5.9 and 5.6 kg. These results indicate that selection for yearling weight can be an efficient tool for improving the growth ability of Zebu cattle.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume IX. Breeding programs for dairy and beef cattle, water buffalo, sheep, and goats., , 419–423, 1986
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