Estimação de componentes de (co)variâncias e predição de DEP's para características de crescimento pós-desmama de bovinos da raça Nelore, usando diferentes modelos estatísticos

Abstract

Foram estimados parâmetros genéticos, fenotípicos e valores genéticos de pesos padronizados aos 365 (P365) e 455 (P455) dias de idade de animais pertencentes ao programa de melhoramento genético da raça Nelore, desenvolvido pelo Departamento de Genética da USP. Quatro modelos foram utilizados para obter estimativas de parâmetros genéticos REML: o modelo 1 incluiu apenas os efeitos genético direto e residual; o 2, incluiu o efeito de ambiente permanente e os efeitos incluídos no modelo 1; o modelo 3 incluiu o efeito genético materno e os efeitos incluídos no modelo 1; o modelo 4 é o completo, com a inclusão dos efeitos genéticos direto e materno e de ambiente permanente. Para P365, as herdabilidades obtidas foram: 0,48, 0,32, 0,28 e 0,27 para os modelos 1, 2, 3 e 4, respectivamente. Para P455, os valores observados foram: 0,48, 0,38, 0,35 e 0,34 para os modelos 1, 2, 3 e 4, respectivamente. A comparação entre os modelos indicou que os efeitos maternos não foram importantes na variação do P455, mas podem ter alguma importância no peso aos 365 dias de idade.

Random regression models in the evaluation of the growth curve of Simbrasil beef cattle

“…This result is in accordance with those of Pelicioni et al (2003), who failed to estimate successfully maternal permanent environmental effects when working with a database of Guzerá cattle with an average number of calves per mother of approximately 1.5 calves for weight at birth, 1.3 calves for ages 30 to 210 days, and 1.2 calves from that age onward. Similar results with the same breed have been observed by Bittencourt et al (2002) and Tanaka et al (2009), who also worked with an average number of calves per cow below 2.…”

Genetic evaluation using multi-trait and random regression models in Simmental beef cattle

“…Pelicioni et al (2003) worked with Guzerá beef cattle, with an average number of calves per dam between 1.2 and 1.5 from birth to mature age, and asserted that it was not possible to estimate the maternal permanent environmental effect. Tanaka et al (2009) and Bittencourt et al (2002) also could not estimate the maternal permanent environmental effect in Guzerá beef cattle in their study with the average number of calves per dam less than 2. Maniatis and Pollott (2003), in their work with Suffolk sheep, affirmed that data with limited structure may be the cause of biologically impossible estimates and that they would need several generations of records and the largest possible amount of relationship information among animals and their dams to obtain more accurate estimates.…”

Genetic parameters for postweaning traits in Braunvieh cattle

“…With regard to genetic parameters for weight at 365 and 450 days of age in the Nellore breed, Bittencourt et al (2002) used a model that included direct and maternal genetic effect, without permanent environmental effect. These authors reported estimates for direct heritability of 0.28 and 0.35 for weight at 365 and 450 days, and 0.10 and 0.07 for maternal heritability at the same ages, respectively.…”

“…Some breeding programs are adopting a new selection criterion for the evaluation of cattle, i.e., postweaning growth (Bittencourt et al, 2002), changing the age of measurement of postweaning growth from 550 to 450 days of age, with the aim of decreasing the generation interval and maximizing the genetic gain. The reduction in the age of measurement and the number of measurements according to Siqueira et al (2003) is of great importance, because it allows the breeders to anticipate the sale of their animals and to select heifers for mating at earlier ages.…”