Variabilidade genética do peso ao nascer e seleção para crescimento em bubalinos do Estado do Pará, Brasil / Genetic variability of birth weight and selection for growth of water buffaloes from State of Pará, Brazil

Birth weight is a performance parameter of great zootechnical importance for both meat and dairy production, as well as for breeding animals, mainly due to its relation to survival rate at weaning, and the weight of animals throughout their developmental and growth phases. Therefore, the objective of this work was to establish heritability estimates, as well as phenotypic and genetic trends of birth weight of water buffaloes from State of Pará, Brazil. Descriptive statistics were calculated and the Shapiro-Wilk Normality test was performed with a Statistical Analysis System package. Heritability estimates were established by Bayesian inference. BW was 36.6 kg in average. The statistical model considered sex, year of birth and breed composition of the animals as fixed effects, and animal, maternal and residual as random effects. Direct heritability was platykurtic (flattened) and with higher asymmetry, presenting a bimodal distribution with the first mode close to 0.10, and the second mode close to 0.30; the maternal heritability was trimodal, with peaks very close to 0.15, and another, less evident, close to 0.20. The direct genetic trend of birth weight was negative (-0.03kg year-1) and maternal genetic trend was close to zero (0.001kg ano-1), even though the phenotypic trend had been positive (0.156 kg year-1). There is genetic variability to be addressed in a breeding program, however, very little was done as far as selection for growth of water buffaloes in the State of Pará.

O peso ao nascer constitui característica produtiva de elevada importância zootécnica, devido à sua relação com a taxa de sobrevivência à desmama e com os pesos nas demais fases de desenvolvimento do animal, quer seja para a produção de carne, leite ou em animais que se destinam à reprodução. O objetivo deste trabalho foi obter estimativas de herdabilidade e tendências fenotípicas e genéticas do peso ao nascer, em bubalinos do Estado do Pará, Brasil. Foram calculadas as estatísticas descritivas e realizado o teste de Normalidade de Shapiro-Wilk por meio do pacote estatístico Statistical Analisys System. As estimativas de herdabilidade foram obtidas por inferência Bayesiana. O peso ao nascer apresentou média de 36,6 kg. O modelo de análise considerou como fixos os efeitos de sexo, ano de nascimento e composição racial do animal e como efeitos aleatórios animal, efeito materno e residual. A distribuição da herdabilidade direta apresentou-se platicúrtica (achatada) e com maior assimetria, tendo uma distribuição bimodal com a primeira moda próxima a 0,10 e a segunda próxima a 0,30; a materna apresentou-se trimodal, com picos bem próximos a 0,15 e outro menos evidente próximo a 0,20. A tendência genética direta do peso ao nascer mostrou-se negativa (-0,03kg ano-1) e a tendência genética materna próxima à zero (0,001 kg ano-1), ainda que a tendência fenotípica tenha sido positiva (0,156kg ano-1). Existe variabilidade genética possível de ser trabalhada em um programa de melhoramento, no entanto, pouco foi feito quanto à seleção para crescimento em búfalos no Estado do Pará.

Association between MUC1 gene polymorphism and expected progeny differences in Nelore cattle (Bos primigenius indicus).

MUC1 is a heavily glycosylated mammalian transmembrane protein expressed by mucosal secretory tissues for both protection against microbial infection and lubrication. An important characteristic of MUC1 is its variable number of tandem repeats (VNTR) containing several sites for O-glycosylation. VNTR length has been associated with many human diseases and with certain economically important traits in domestic ruminants. The aim of the present study was to correlate the length of MUC1 gene VNTR with expected progeny differences (EPDs) obtained for growth, fertility and carcass traits. Five alleles were identified, with alleles containing short VNTRs being more frequent than those with long, thereby demonstrating that Brazilian Nelore cattle are characterized by high frequencies in short MUC1 VNTRs. Statistical analyses revealed there to be no significant association between VNTR length and EPDs for weight at 120 days (W(120) ), scrotal circumference at 365 (SC (365) ) and 450 (SC (450) ) days, age at first calving (AFC), and rib eye area (REA).

Association between MUC1 gene polymorphism and expected progeny differences in Nelore cattle (Bos primigenius indicus)

MUC1 is a heavily glycosylated mammalian transmembrane protein expressed by mucosal secretory tissues for both protection against microbial infection and lubrication. An important characteristic of MUC1 is its variable number of tandem repeats (VNTR) containing several sites for O-glycosylation. VNTR length has been associated with many human diseases and with certain economically important traits in domestic ruminants. The aim of the present study was to correlate the length of MUC1 gene VNTR with expected progeny differences (EPDs) obtained for growth, fertility and carcass traits. Five alleles were identified, with alleles containing short VNTRs being more frequent than those with long, thereby demonstrating that Brazilian Nelore cattle are characterized by high frequencies in short MUC1 VNTRs. Statistical analyses revealed there to be no significant association between VNTR length and EPDs for weight at 120 days (W120), scrotal circumference at 365 (SC365) and 450 (SC450) days, age at first calving (AFC), and rib eye area (REA).

Parâmetros genéticos para idade ao primeiro parto estimados por diferentes modelos para rebanhos da raça Nelore / Genetic parameters for age at first calving estimated by different models for Nellore breed herds

Com objetivo de estimar parâmetros genéticos e estudar a utilização de diferentes efeitos em avaliações genéticas para idade ao primeiro parto (IPP) por diferentes modelos, foram utilizados registros de IPP de animais da raça Nelore, nascidos entre os anos de 1990 e 2005. Foram considerados os seguintes modelos (M): M1, incluindo o efeito fixo de GC1 (constituído pelos animais nascidos na mesma fazenda e ano), além da covariável, peso aos 365 dias de idade (efeito linear e quadrático), totalizando 24.263 registros de IPP; M2, considerando os efeitos fixos de GC1, ano e estação de parição, totalizando 59.792 registros de IPP e M3, incluindo os efeitos fixos de GC2 (agrupando os animais nascidos na mesma fazenda, ano e que conceberam no mesmo manejo reprodutivo), ano e estação de parição, totalizando 59.792 registros de IPP. As estimativas dos componentes de variância e herdabilidade e os valores genéticos (VG) foram obtidos pelo método da máxima verossimilhança restrita, com a inclusão da matriz de parentesco disponível. As diferenças esperadas na progênie (DEPs) foram obtidas dividindo os VG por dois. Após a obtenção desses resultados, foram realizadas correlações entre os VG e o ranqueamento das DEPs dos reprodutores para IPP, utilizando-se o procedimento PROC CORR (SAS, 2003). Ao se considerar o ano e a estação de parto nos modelos de análise (M2 e M3), esses produziram um maior R², indicando que tais modelos conseguiram explicar, em maior grau, as diferenças existentes entre os animais para IPP. As herdabilidades estimadas foram de baixa magnitude (0,14 e 0,15). As correlações entre os VG obtidas por diferentes modelos foram 0,73 (M1 x M2); 0,91 (M2 x M3) e 0,66 (M1 x M3).

With the objective of estimate genetic parameters and study the utilization of different effects on the genetic evolution for the age of the first calving (AFC) by different models, they were used AFC records from Nellore breed animals, born from 1990 to 2005. They were considered the following models (M): M1, including the fixed effect of the contemporary group (CG), CG1 (grouping the animals that were born at the same farm and year), besides the co variable, weight at 365 days of age (linear and quadratic effects), totalizing 24,263 records of AFC; M2, considering the effects of CG1, year and season of the calving, totalizing 59,792 records of AFC and M3, including effects CG2 (grouping the animals born at the same farm, year and submitted at the same reproductive management), year and season of calving totalizing 59,792 records of AFC. The components of variance and Genetic Value (GV) were obtained by Restricted Maximun Likelihood Method, with the inclusion for the relationship matrix. The Differences Expected on the Progeny (DEPs) were obtained by dividing the GV by two, after this they were estimated the correlations between GV and ranks of the reproductor's DEPs for AFC, utilizing the procedure CORR (SAS, 2003). While considering year and season of calving in the analysis models (M2 and M3), it was produced a bigger R², indicating that those models could explain, in a larger scale, the existing differences between the animals for AFC. The heritabilities estimated were of low magnitude (0,14 and 0,15). The correlations between the GV obtained by the different models were .73 (M1 x M2); .91 (M2 x M3) and .66 (M1 x M3).

Mitochondrial DNA single nucleotide polymorphism associated with weight estimated breeding values in Nelore cattle (Bos indicus)

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 percent for tRNAasn, 95.23 percent for tRNAleu and 90.62 percent 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.

Structure and genetic variability in Nellore (Bos indicus) cattle by pedigree analysis

Parameters based on the probability of gene origin were used to describe the genetic variability in strains of Nellore and polled Nellore (Bos indicus) cattle that participated in the Program for Genetic Improvement of the Nellore Breed (Programa de Melhoramento Genético da Raça Nelore). The effective number of founders was 87.2 for Nellore and 107.9 for polled Nellore, while the number of ancestors was 59.8 for Nellore and 61.5 for polled Nellore and the remaining genomes were 39.4 for Nellore and 34.5 for polled Nellore cattle. The results indicate an intense use (by artificial insemination) of some sires and the absence of subdivisions in the population. The family structure in the two breeds was mainly caused by the genetic contribution of the same sires and only mating preferences for descendants of some founders are recorded in either breed. The results suggest that genetic variability needs monitoring in order to avoid the compromise of genetic improvement in economically important traits in the breeding program.