Seleção para peso pós-desmame em nelore e guzerá: 'seleção praticada e resposta em 15 anos de progênies'
Autores
Alexander George Razook, Leopoldo Andrade de Figueiredo, Luiz Martins Bonilha Neto, José Benedito de Freitas Trovo, Irineu Umberto Packer, Laércio José Pacola, Joslaine Noely dos Santos Gonçalves Cyrillo, Ana Cláudia Ruggieri e Maria Eugênia Zerlotti
Resumo
Selection for yearling weight has been applied in two (120-cow, 6-sire) purebred herds of 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 (Y378) and heifer’s weight at 550 d (Y55O). Average age of parents were 5.05; 5.09 and 5.09 yr for NeS, NeC and GUS, respectively. For calves born in 1995, the midparent cumulative selection differentials in standard units were 4.05 in NeS; 0.36 in NeC and 3.24 in GuS.
Annualy genetic trends for Y378 ranged from 2.68 to 2.96 kg/year (0.10 sdu) and from 2.20 to 2.53 kg/year (0.08 sdu) respectively for NeS and GuS. For Y550 the values ranged from 2.63 to 2.81 kg/year (0.12 sdu) and 1.37 to 2.15 kg/year (0.06 sdu) respectively for NeS and GuS.
Realized’ h²r for Y378 were 0.45 and 0.42 respectively for NeS and GuS. For Y550 values ranged from 0.42 to 0.55 and 0.27 to 0.33 for NeS and GuS respectively. These results indicate that selection for yearling weight can be an efficient tool for improving the growth ability of Zebu cattle.
Anais do 6º World Congress on Genetics Applied to Livestock Production, Armidale, NSW, Austrália, Janeiro 1998, 23:133-136.
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