Thaymisson Santos de Lira

Interação genótipo-ambiente para características sob efeito maternal na raça Nelore nos estados do Maranhão, Mato Grosso e Pará

This study was carried out to analyze genotype-environment interaction for maternal effect traits weights of Nellore cattle from Maranhao (MA), Mato Grosso (MT) and Para (PA) States. It was used records of 37,032 animals provided by Genetic Improvement Program of Nellore (PMGRN-ANCP) collected between the years 1993 to 2010. The means and standard deviations for W120 to MA, MT and PA were 123.43 ± 17.06, 133.91 ± 19.62 and 130.07 ± 16.03kg and to W210 for the same States were 181.83 ± 34.15, 28.52 ± 194.73 and 189.76 ± 23.45kg, respectively. Genetic correlations estimative between the expected progeny difference for same sire were 0.42 (MA-MT), 0.38 (MA-PA) and 0.70 (MT-PA) for P120; 0.49 (MA-MT), 0.13 (MA-PA) and 0.40 (MT-PA) for P210. Lower genetic correlations in both traits were observed between Maranhao and Para states, which presented greats environmental distinctions. These results showed genotype-environment interaction and reaffirm the current preoccupation with these interaction which can be effect the genetic evaluation of animals raised in this states.

Estimação de parâmetros genéticos entre pesos pré e pós-desmama na raça Nelore

As correlacoes entre duas ou mais caracteristicas estimam o nivel de uniao entre elas, sendo a origem e a grandeza da relacao existente de grande importância, pois visam aprimorar o material genetico de um conjunto de caracteres que agem simultaneamente. Os objetivos foram: estimar os componentes de variância e herdabilidade para os pesos padronizados aos 120, 240, 365, 450 e 550 dias de idade (P120, P240, P365, P450 e P550, respectivamente) e estimar a correlacao genetica entre o P120 e os outros pesos citados. Foram utilizadas 29769 observacoes de bovinos da Raca Nelore, em analises uni e bi-carater. Estas ultimas, com o P120 como caracteristica principal e a covariância aditiva fixada, estrategicamente, com o intuito de se obter estimativas de correlacoes geneticas. Os valores estimados de herdabilidades foram: 0,21 (P240); 0,37 (P365); 0,36 (P450) e 0,42 (P550). Para o P120, as estimativas variaram de 0,23 a 0,31. Os valores das correlacoes geneticas entre o P120 e os outros pesos foram altos e positivos: 0,96 (P240); 0,87 (P365); 0,79 (P450) e 0,76 (P550), sugerindo que a selecao para pesos em idade mais jovens promovera o aumento dos pesos posteriores.

Impacto da heterogeneidade de variância residual na avaliação genética de rebanho Nelore no Bioma Amazônia

This study was carried out to evaluate the effects of heterogeneity of residual variance on genetic evaluation of cattle raised on pasture from Amazonia Bioma, Brazil. Adjusted weights at weaning weight (205 days of age) were sorted in three phenotypic classes: low (less than average weight), medium (between the average and the average plus one standard deviation) and high (greater than average plus one standard deviation). There was increased of genetic additive direct and residual variances to the extent that increased phenotypic classes. The heritabilities for low, medium and high phenotypic classes were 0.27, 0.33 and 0.26, respectively. These estimates suggest that mass selection could result in genetic gain on breeding program that use weaning weight as a selection criteria. Genetic correlations between the low and medium, low and high, and medium and high phenotypic classes were 0.82, 0.35 and 0.72, respectively. The estimate of correlation of the breeding values of sire shown effect of the heterogeneity of phenotypic variance on the prediction of animals breeding values. There was a major variability for the breeding values of sires at high phenotype class. Thus, we suggested the identification and selection of sires with the highest breeding values for weaning weight, according with environment in which these animals are being raised.