Estimativa de ganho genético a partir de diferenciais de seleção e parâmetros populacionais em um rebanho Caracu
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Data
2005-12-01
Autores
Pereira, Márcio Cinachi [UNESP]
Mercadante, Maria Eugênia Zerlotti
Albuquerque, Lucia Galvão de [UNESP]
Razook, Alexander George
Título da Revista
ISSN da Revista
Título de Volume
Editor
Sociedade Brasileira de Zootecnia
Resumo
Foram analisados dados do rebanho Caracu da Estação Experimental de Zootecnia de Sertãozinho, selecionado para peso ao sobreano entre os anos de 1979 e 2002, com os objetivos de descrever o tamanho efetivo, o coeficiente de geração, o intervalo de gerações e os diferenciais de seleção e estimar o ganho genético. O ganho genético por ano foi obtido multiplicando-se o produto do diferencial de seleção ponderado médio (em kg) pela herdabilidade e dividindo-se pelo intervalo de geração médio. Diferenciais de seleção ponderados médios para seleção direta para peso ao sobreano, de touro e vaca, foram, respectivamente, iguais a 1,10 e 0,28 unidades de desvio-padrão (u.d.p.) e os diferenciais de seleção acumulados de touro e vaca para a progênie de 2001 foram iguais a 3,61 e 2,32 u.d.p. A razão da média dos diferenciais de seleção não-ponderado e máximo dos touros foi 0,89, indicando perda de eficiência de 11%, decorrente sobretudo da não-seleção em um mesmo ano de animais de mesma família. O intervalo de geração para os períodos de 1979 a 1984, 1985 a 1990, 1991 a 1996 e 1997 a 2002 foram 6,3; 6,3; 5,5 e 4,8 anos, respectivamente, e a progênie nascida em 2002 atingiu, em média, 4,5 gerações de seleção. O coeficiente de endogamia médio anual da população foi 0,50% e para os animais endogâmicos de 1,83%. O tamanho efetivo populacional para os quatro períodos foi de 9, 12, 20 e 64. em função da seleção praticada, a estimativa do ganho genético anual para peso ao sobreano foi 2,02 kg/ano. A introdução de material genético, a restrição ao grau de parentesco nos acasalamentos e a seleção de, no máximo, dois filhos de cada reprodutor por ano foram eficazes no controle do aumento excessivo da endogamia.
Data from the Caracu herd of Sertãozinho Experimental Station, selected for post weaning weight between 1979 and 2002, was analyzed to describe effective size, generation coefficient, generation interval, selection differentials and genetic gain in this population. Genetic gain was estimated by the product of the average weighted standardized differential (kg) and heritability divided by the average generation interval. Averages of sire and dam weighted selection differentials for post weaning weights were 1.10 and 0.28 standard deviations units (s.d.u). Sire and dam cumulative selection differentials measured in the progenies born in 2001 were 3.61 and 2.32 s.d.u, respectively. The ratio between averages of unweighted and maximum sire selection differentials was 0.89 indicating a efficiency loss of 11% mainly due to avoiding selection of related animals in the same year. Estimates of generation interval for the periods 1979 - 1984, 1985 - 1990, 1991 - 1996 and 1997 - 2002, were 6.3, 6.3, 5.5 and 4.8 years, respectively. In the same order, population effective size was 9, 12, 20 and 64 for these periods.The generation coefficient for the progeny born in 2002 was 4.5 generations. Average annual inbreeding of the population was 0.50% and 1.83% for inbred animals. The annual estimated genetic gain by selection for yearling weight was 2.02 kg/year. The introduction of genetic material from other herds, the restriction to avoid mating of related animals and the selection of a maximum of two progeny/sire/year were effective to avoid larger increase of inbreeding.
Data from the Caracu herd of Sertãozinho Experimental Station, selected for post weaning weight between 1979 and 2002, was analyzed to describe effective size, generation coefficient, generation interval, selection differentials and genetic gain in this population. Genetic gain was estimated by the product of the average weighted standardized differential (kg) and heritability divided by the average generation interval. Averages of sire and dam weighted selection differentials for post weaning weights were 1.10 and 0.28 standard deviations units (s.d.u). Sire and dam cumulative selection differentials measured in the progenies born in 2001 were 3.61 and 2.32 s.d.u, respectively. The ratio between averages of unweighted and maximum sire selection differentials was 0.89 indicating a efficiency loss of 11% mainly due to avoiding selection of related animals in the same year. Estimates of generation interval for the periods 1979 - 1984, 1985 - 1990, 1991 - 1996 and 1997 - 2002, were 6.3, 6.3, 5.5 and 4.8 years, respectively. In the same order, population effective size was 9, 12, 20 and 64 for these periods.The generation coefficient for the progeny born in 2002 was 4.5 generations. Average annual inbreeding of the population was 0.50% and 1.83% for inbred animals. The annual estimated genetic gain by selection for yearling weight was 2.02 kg/year. The introduction of genetic material from other herds, the restriction to avoid mating of related animals and the selection of a maximum of two progeny/sire/year were effective to avoid larger increase of inbreeding.
Descrição
Palavras-chave
effective size, generation interval, inbreeding coefficient, generation coefficient, Post-weaning weight, Selection, Peso pós-desmame, tamanho efetivo, intervalo de gerações, coeficiente de endogamia, coeficiente de geração, Seleção
Como citar
Revista Brasileira de Zootecnia. Sociedade Brasileira de Zootecnia, v. 34, n. 6, p. 2245-2252, 2005.