Tendências genéticas e seleção para eficiência à desmama em bovinos da raça Aberdeen Angus

• Ano de defesa: 2011
• Autor(a) principal: Campos, Leonardo Talavera
• Orientador(a): Dionello, Nelson José Laurino
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Pelotas
• Programa de Pós-Graduação: Programa de Pós-Graduação em Zootecnia
• Departamento: Faculdade de Agronomia Eliseu Maciel
• País: BR
• Palavras-chave em Português: Diferença esperada na progênie; Ganhos de peso; Herdabilidade; Índices de seleção; Peso metabólico; Relação
• Palavras-chave em Inglês: Expected progeny difference; Heritability; Metabolic weight; Ratio; Selection indexes; Weight gains
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA
• Link de acesso: https://guaiaca.ufpel.edu.br/handle/123456789/2584

Study was divided into two independent and complementary parts. The first objective was to evaluate the behavior of additive genetic trends for weight traits and selection indices in cattle population of Aberdeen Angus breed evaluated in PROMEBO®. Data were provided by the National Breeders Association (ANC), with animals produced from 1974 to 2010. The traits were: birth weight (BW), with 70,156; weight gain from birth to weaning (WWG), with 181,491; and post-weaning weight gain (PWG), with 113,323 animals, respectively. Characteristics were pre-adjusted for known environmental effects. Other variables were the weaning and final selection indexes. It was includes, beside WWG and PWG, scrotal circumference (SC) in the final stage (yearling) and visual scores collected at the weaning and yearling. Weighting percentages were applied for index constituents. The statistical model included additive genetic effects of sire and dam and environmental effects of contemporary groups. The estimates were obtained by Method GenSys, using a denomined gametic model on univariate analysis. In regression analysis using arithmetic means of breeding values or EPDs was used the least squares method weighted by the number of observations, obtained by PROC REG (SAS, 1996). Significant additive direct genetic trends estimated to the weight characters WWG, PWG and weight gain from birth to yearling (YWG = WWG + PWG) and selection indices at weaning and yearling, show that, as selection criteria, are providing moderate genetic progress in this population of Angus. Results for birth weight suggested that it is almost stabilized, which is desirable in order to avoid calving problems. The second part of the study was to evaluate a selection criterion for efficiency to weaning in beef cattle herds controlled by PROMEBO®. This criterion was the relationship between weight gain from birth to weaning of calves (WWG) and cow weight (CW), obtained in two ways, appear in the denominator of equation (1) real cow weight at weaning of their product, a percentage expressing this efficiency (EFF), or (2) metabolic weight of cow at weaning from each of their calves, resulting in the efficiency in metabolic weight (EMW). The bulls were evaluated by calves who have greater WWG (output), compared to the cost of production ("input"), measured by the metabolic weight of their mother cows for EMW, or actual bodyweight of cows for EFF. Records from performance data including weight of 10,350 calves and their mothers, referring to the progenies of 330 sires from Angus breed, produced between 1982 to 2002, in three herds from two farms located in the region Frontier West of Rio Grande do Sul. The mixed model solutions were obtained through a computer program PROC MIXED (SAS Institute Inc., 2001). The heritability was estimated by covariance between paternal half-siblings. The heritability estimates, of moderate magnitude, were 0,187±0,023 (18,69%) for EMW and 0,167±0,022 (16,73%) for EFF. Despite of difficulties and constraints statistics, selection criteria for efficiency analysis, in particular, efficiency in metabolic weight (EMW), showed reasonable heritability. This opens prospects for allowing a selection of sires that provide a greater return and economic efficiency, transmitting to their offspring genetic potential for a greater weight gain in relation step to the maintenance requirements of cows, mothers of their products. Ratios as EFF and EMW, due positive association with feed efficiency, indicate that were an important alternative for selection because the moderate heritability and ease of measurement in practice.