Com o objetivo de se comparar o ajustamento de modelos com diferentes definições de grupos contemporâneos sobre as estimativas de (co)variâncias e parâmetros genéticos para pesos padronizados e reais aos 120 e 210 dias de idade, analisaram-se dados de 72.731 bezerros Nelore, machos e fêmeas, nascidos de 1985 a 2005 em 40 rebanhos integrantes do PMGRN - Nelore Brasil. Foram comparados quatro modelos incluindo diferentes estruturas de grupos contemporâneos (CG), julgados pelos critérios de informação de Akaike, Bayesiano e modificado de Akaike. As estimativas foram obtidas pelo método da máxima verossimilhança restrita livre de derivadas. As estimativas de (co)variâncias e parâmetros genéticos foram similares entre os modelos, porém os critérios de informação (BIC, CAIC) indicaram que o modelo mais adequado é o que considera o grupo contemporâneo como efeito aleatório, sendo este constituído pela concatenação dos efeitos de rebanho, ano de nascimento, grupo de manejo e efeito sazonal de trimestre de nascimento, e com efeito do sexo do bezerro independente do CG.

We used actual and adjusted weights to 120 d and 210 d of age of 72,731 male and female Nellore calves born in 40 PMGRN - Nellore Brazil herds from 1985 to 2005 aiming to compare the effect of different definitions of contemporary groups on estimates of (co)variance and genetic parameters. Four models, each one with a different structure of contemporary group (CG), were compared using the Akaike Information Criterion (AIC), the Bayesian Information Criterion (BIC), and the Consistent Akaike Information Criterion (CAIC). (Co)variance estimates were obtained using a derivative-free restricted maximum likelihood procedure. Estimates of (co)variances and genetic parameters were similar for the four models considered. However, the BIC and CAIC indicated that the most appropriate model for this Nellore population was the one that considered CG to be random, and sex of calf to be fixed and separate from CG, in which CG was defined as the group of calves born in the same herd, year, season of birth (trimester), and undergone the same management.

The objective of this research was to estimate the relative magnitude of effects included in contemporary groups (CG) and their interactions with adjusted and actual 120 d and 210 d weights in 72, 731 male and female Nelore calves born from 1985 to 2005 in 40 herds from PMGRN (Genetic Improvement Program of Nelore). Ten models with different CG structures were compared. The analyses were done using the general linear models (GLM) procedure run in SAS software. All of the effects included in the CG for each model were significant (p < 0.001) for the four traits analyzed. Inclusion of semester or trimester of birth as part of a CG was more appropriate than its use as an independent effect in the model because it accounted for interactions with the other effects in the CG. Calf sex (CS) and dam age at calving (DAC) had similar effects across the models, which suggested independence from other effects in these models. The corresponding age deviation effect had a larger impact on actual weight at 120 d than any other effect in all of the models tested. The use of actual weights in models with no CS effect in CG provides an alternative that would allow better genetic connectedness among CGs and greater accuracy in genetic evaluations.

We sampled 119 Nelore cattle (Bos indicus), 69 harboring B. indicus mtDNA plus 50 carrying Bos taurus mtDNA, to estimate the frequencies of putative mtDNA single nucleotide polymorphisms (SNPs) and investigate their association with Nelore weight and scrotal circumference estimated breeding values (EBVs). The PCR restriction fragment length polymorphism (PCR-RFLP) method was used to detect polymorphisms in the mitochondrial asparagine, cysteine, glycine, leucine and proline transporter RNA (tRNA) genes (tRNAasn, tRNAcys, tRNAgly, tRNAleu and tRNApro). The 50 cattle carrying B. taurus mtDNA were monomorphic for all the tRNA gene SNPs analyzed, suggesting that they are specific to mtDNA from B. indicus cattle. No tRNAcys or tRNAgly polymorphisms were detected in any of the cattle but we did detect polymorphic SNPs in the tRNAasn, tRNAleu and tRNApro genes in the cattle harboring B. indicus mtDNA, with the same allele observed in the B. taurus sequence being present in the following percentage of cattle harboring B. indicus mtDNA: 72.46% for tRNAasn, 95.23% for tRNAleu and 90.62% for tRNApro. Analyses of variance using the tRNAasn SNP as the independent variable and EBVs as the dependent variable showed that the G -> T SNP was significantly associated (p < 0.05) with maternal EBVs for weight at 120 and 210 days (p < 0.05) and animal's EBVs for weight at 210, 365 and 455 days. There was no association of the tRNAasn SNP with the scrotal circumference EBVs. These results confirm that mtDNA can affect weight and that mtDNA polymorphisms can be a source of genetic variation for quantitative traits.

Restriction fragment length polymorphism (RFLP) has been detected at the bovine kappa-casein locus. The polymorphism has been analyzed for its effects in cattle production, mostly for milk traits and even for maternal effect on pre-weaning weights. We used polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) to genotype 408 Nellore animals for the non-silent mutation (Thr/Ile136 and Asp/Ala148) that characterizes the A and B variants of the polymorphism and compared expected progeny difference (EPD) for a maternal effect on 120 and 210 days weights and direct EPD for 120, 210, 450 and 550 day weight between AA and AB animals. The EPD values were obtained from the University of São Paulo (Brazil) Nellore Cattle Breeding Program, which evaluated 266,272 animals in 2001. Analysis of Variance was used to compare weight expected progeny differences (EPDs) between animals genotyped as AA and AB. The A allele frequency was 0.911. Although the AA animals had higher weight EPDs than AB animals the differences were not statistically significant (p > 0.05).