Avaliação genética da produção de leite e de características reprodutivas de bovinos da raça Girolando

• Ano de defesa: 2013
• Autor(a) principal: Cayo, Ali William Canaza
• Orientador(a): Lopes, Paulo Sávio
• Banca de defesa: Silva, Fabyano Fonseca e , Carneiro, Antônio Policarpo Souza , Cobuci, Jaime Araujo
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Genética e Melhoramento
• Departamento: Genética animal; Genética molecular e de microrganismos; Genética quantitativa; Genética vegetal; Me
• País: BR
• Palavras-chave em Português: Bovino; Endogamia; Lactação curta; Parâmetros genéticos; Tendência genética; Persistência da lactação
• Palavras-chave em Inglês: Cattle; Inbreeding; Lactation short; Genetic parameters; Genetic trend; Lactation persistency
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::GENETICA E MELHORAMENTO DOS ANIMAIS DOMESTICOS
• Link de acesso: http://locus.ufv.br/handle/123456789/1378

The objectives of the present study were: i) to evaluate the genetic structure and diversity of the population; ii) to evaluate the effect of inclusion or non-inclusion of short-lactations and the effect of the cow (CBG) and/or dam (DBG) breed groups in models for genetic evaluation of 305-day milk yield (305MY) and reproductive traits; iii) to estimate heritability and genetic, phenotypic and environmental correlations between 305MY and the reproductive traits; iv) to estimate the genetic trends for 305MY and reproductive traits; and v) to estimate the (co)variance components and genetic parameters for test-day milk yield (TDMY) via random regression model (RRM) and evaluate different measures of lactation persistency in Girolando cattle. The reproductive traits studied were age at first calving (AFC), first calving interval (FCI) and length of the dry period (LDP). The coefficients of population structure and genetic diversity were obtained with software Endog, whereas the estimates of the (co)variance components and genetic parameters were obtained with the program Wombat. Inbreeding and average relatedness coefficients of the Girolando population were 0.11 and 0.13%, respectively. The estimate of effective population size considering the complete generations traced was 188, which is above the critical level. The heritability estimates for 305MY, AFC and FCI varied from 0.23 to 0.29, from 0.40 to 0.44 and from 0.13 to 0.14, respectively, without the inclusion of short lactations; and from 0.23 to 0.28, from 0.39 to 0.43 and from 0.13 to 0.14, respectively, whey they were included. The models which included the fixed effects of CBG or DBG had higher heritability estimates for all traits studied than the models that considered both effects simultaneously (CBG and DBG). The heritability estimates were similar between the single- and bi-trait analyses, and varied from 0.20 to 0.28, 0.00 to 0.08 and 0.07 to 0.14, for 305MY, FCI and LDP, respectively, whereas for AFC it was 0.20. The genetic correlations between 305MY with AFC (- 0.49) or LDP (-0.40 to -0.79) showed favorable association. However, antagonistic genetic association was verified between 305MY and FCI (0.59) at the first calving, although with low accuracy. The phenotype and environment correlations between 305MY and AFC or LDP showed favorable association (-0.25 to -0.42 and -0.14 to - 0.44, respectively). The annual genetic change in 305MY and AFC when the four selection paths were combined were 7.40 kg milk/year and -0.13 days/year in the period from 1979 to 2007. The fit quality criteria adopted indicated the RRM with Legendre polynomials of orders 3 and 5 to model the additive genetic and permanent environment effects, respectively, as the best model to describe the variation of the random effects. The heritability and genetic correlation estimates for TDMY throughout the lactation, obtained with the chosen model, varied from 0.18 to 0.23 and -0.03 to 1.00, respectively. Among nine measures of lactation persistency, PS7 showed highest heritability estimate and lowest genetic correlation with 305MY. In conclusion, the inbreeding in the Girolando breed was of small magnitude, indicating that the mating practices were appropriate during the period assessed; the inclusion of short-lactation records causes little variation in the variance components and in the heritabilities of the studied traits, and it is recommended to use the model with fixed effect of CBG and inclusion of records from short-lactations in the genetic evaluation for 305MY, AFC and FCI of Girolando cattle; antagonistic genetic association between 305MY and AFC was observed, indicating that the emphasis of selection for milk yield would have increased calving interval as a correlated response, and a wide genetic variation for milk production and reproductive traits can allow for moderate genetic gains, thereby contributing, in the long term, to improvement in productive and reproductive efficiency in the Girolando herds; the results of genetic trends showed that the genetic improvement program of the breed promoted improvement in milk yield and reduction in the age of the cow at first calving, not having an impact on the first calving interval of Girolando cows; the use of the measure of persistency (PS7) proposed by Kistemaker (2003) with RRM employing Legendre polynomial functions of the third and fifth orders for the additive genetic and permanent environmental effects, respectively, would be the most suitable option for the evaluation of lactation persistency in Girolando animals.