Genetic parameter and genetic trend estimates for reproductive traits in Wistar rats / [Estimativas de parâmetros genéticos e tendências genéticas de características reprodutivas em ratos Wistar]

The aim of this study was to estimate genetic parameters and genetic trends for reproductive traits in Wistar rats. A total of 1,167 data records from 283 females over six generations of monogamous mating pairs was used. Heritability and genetic correlation were estimated through Bayesian inference and genetic trends were calculated by linear regression of breeding values over generations. Heritability estimates for litter size at birth (LS), calving interval (CI), pup mortality (PM) and maternal cannibalism (CAN) presented low magnitude, ranging from 0.01 to 0.13. CAN presented high and positive genetic correlation with LS and PM (0.77 and 0.78, respectively). On the other hand, all the other estimated genetic correlations were not significant. Genetic trend was positive for LS (+0.0900 pups per generation), and negative for PM and CAN (-1.0085 and -0.5217 pups per generation, respectively). For CI the genetic trend was not significant. It is recommended to increase selection intensity on dams in this Wistar rat population in order to accelerate the genetic progress.(AU)

O objetivo deste estudo foi estimar os parâmetros genéticos e as tendências genéticas de características reprodutivas em ratos Wistar. Foram analisados 1.167 registros coletados em 283 fêmeas ao longo de seis gerações de pares de acasalamentos monogâmicos. Herdabilidade e correlação genética foram estimadas por meio de inferência bayesiana, e as tendências genéticas foram calculadas pela regressão linear dos valores genéticos em função das gerações. As estimativas de herdabilidades para as características número de filhotes nascidos (LS), intervalo de parto (CI), mortalidade de filhotes (PM) e canibalismo materno (CAN) foram de baixa magnitude (0,01 a 0,13). CAN apresentou correlação genética alta e positiva com LS e PM, 0,77 e 0,78, respectivamente. As demais correlações genéticas estimadas foram não significativas. A tendência genética foi positiva para LS (+0,0900 filhote por geração) e negativa para PM e CAN (-1,0085 e -0,5217 filhote por geração, respectivamente). A tendência genética não foi significativa para CI. Recomenda-se aumentar a intensidade de seleção nas fêmeas nessa população de ratos Wistar, a,fim de acelerar o progresso genético.(AU)

Utilização de modelos unicaracterística e multicaracterística na estimação de parâmetros genéticos na raça Nelore / Utilization of single-trait and multi-trait models applied to genetic parameter estimation in Nellore Cattle

Estimativas dos parâmetros genéticos e dos componentes de covariância para peso ao nascimento (PN), peso à desmama (PD), circunferência escrotal (CE), ganho de peso pós-desmama (GP) e musculosidade (MUSC) foram obtidas com modelos unicaracterística, bicaracterística e multicaracterística, utilizando-se um banco de dados de 69.525 animais da raça Nelore. Os parâmetros foram estimados pelo método da máxima verossimilhança restrita, com modelos que incluíram o efeito genético aditivo direto e materno, além do grupo de manejo a desmama e de ambiente permanente da vaca, todos como aleatórios, e do efeito fixo de grupo de contemporâneo. Os coeficientes de herdabilidade estimados para as características pós-desmama com o modelo multicaracterística (0,45; 0,31 e 0,25, respectivamente, para CE, GP e MUSC) foram maiores que as estimativas obtidas com os modelos unicaracterística (0,42; 0,21 e 0,22) e bicaracterística (0,39; 0,25 e 0,24). Da mesma forma, as correlações genéticas estimadas foram, em grande parte, maiores para o modelo multicaracterística. Estes resultados indicam que a redução do viés, proporcionada pelo modelo multicaracterística, aumenta as estimativas dos parâmetros genéticos e demonstra que os resultados com análises unicaracterística e bicaracterística são subestimados. Os resultados da resposta à seleção demonstraram que a musculosidade apresentou grande potencial seletivo, e o cálculo das respostas correlacionadas de musculosidade e demais características estudadas demonstrou que sua utilização em programas de seleção pode ser vantajosa aos criadores...

Genetic parameters and components of (co)variance for birth weight (BW), weaning weight (WW), scrotal circumference (SC), weight gain at post-weaning (WG), and muscle score (MUSC) were obtained with univariate, bivariate and multivariate models, using a dataset of 69,525 Nellore cattle. The parameters were estimated by restricted maximum likelihood method. Direct and maternal additive genetic effects, group of management, and maternal permanent environmental effect were adjusted as random effects, while contemporary group was adjusted as fixed effect. Multivariate approach allowed higher estimate heritability for postweaning traits (0.45; 0.31 and 0.25, respectively for SC, WG and MUSC) than univariate (0,42; 0,21 and 0,22) and bivariate models (0,39; 0,25 and 0,24). Similarly, the genetic correlations were higher in the multivariate approach. These results indicate that reducing the bias provided by the mutivariate model improves the estimates of genetic parameters and shows that the results of bivariate and univarite models are underestimated. Selection for muscle score presented great potential for correlated response in other traits and its use in selection programs can be a useful tool for breeders...

Inclusão da epistasia em modelo de avaliação genética de bovinos de corte compostos / The effect of the inclusion of epistasis on the genetic evaluation model of beef cattle composite

Dados de bovinos compostos foram analisados para avaliar o efeito da epistasia nos modelos de avaliação genética. As características analisadas foram os pesos aos 205 (P205) e 390 dias (P390) e perímetro escrotal aos 390 dias (PE390). As análises foram realizadas pela metodologia de máxima verossimilhança considerando-se dois modelos: o modelo 1 incluiu como covariáveis os efeitos aditivos diretos e maternos, e os não aditivos das heterozigoses para os efeitos diretos e para o materno total, e o modelo 2 considerou também o efeito direto de epistasia. Para comparação dos modelos, foram utilizados o critério de informação de Akaike (AIC) e o critério de informação Bayesiano de Schwartz (BIC), e o teste de razão de verossimilhança. A inclusão da epistasia no modelo de avaliação genética pouco alterou as estimativas de componentes de (co)variâncias genéticas aditivas e, consequentemente, as herdabilidades. O teste de verossimilhança e o critério de Akaike sugeriram que o modelo 2, que inclui a epistasia, apresentou maior aderência aos dados para todas as características analisadas. O critério BIC indicou este modelo como o melhor apenas para P205. Para análise genética dessa população, o modelo que considerou o efeito de epistasia foi o mais adequado.

Composite bovine data was analyzed with the objective of evaluating the effect of the epistasis parameter in the models of genetic evaluation. The analyzed characteristics were weight at 205 (W205) and 390 days (P390), and scrotal circumference at 390 days (SC390). The analysis were done by the maximum likelihood method, considering two models: model 1, which included as covariates the direct and maternal additive effects, and non-additive of the heterozygosis for the direct and total maternal, and model 2, which also considered the direct epistasis direct. The Akaike Information Criteria (AIC) and the Bayesiano of Schwartz Information Criteria (BIC) were used for the comparison of the models and the test of ratio of likelihood. The inclusion of the epistasis effects on the model of the genetic evaluation did not alter much the estimation of the genetic additive (co)variances components and, consequently the heritability. However, it was significantly superior by the likelihood ratio test for the studied characteristics. Through the BIC, model 2 was more adequate only for W205. For the genetic analysis of that population the model that considers the epitasis is the more adequate.

Influência da interação genótipo x ambiente sobre o peso à desmama em bovinos da raça Nelore / Influence of genotype x environment interaction on weaning weight in Nellore cattle

Avaliaram-se os efeitos da interação genótipo x ambiente sobre a característica peso à desmama em bovinos da raça Nelore. Foram analisados 45.697 registros de peso à desmama ajustados para 205 dias, originários de três fazendas. Estas foram organizadas em duplas e analisadas por meio de análises de características únicas, considerando cada dupla como um só rebanho. Em seguida, as mesmas duplas foram submetidas a análises de características múltiplas, em que o peso à desmama de cada fazenda foi considerado como característica distinta dentro de sua respectiva dupla. Os componentes de variância foram estimados por máxima verossimilhança restrita, utilizando-se o programa MTDFREML. Os coeficientes de correlação genética encontrados variaram de 0,79 a 1,00. Foram também estimadas as diferenças esperadas de progênies (DEPs), utilizando-se o mesmo programa computacional. Posteriormente, os touros foram ordenados conforme os valores de suas respectivas DEPs, selecionando-se os 30 por cento mais bem classificados. Com base nas DEPs, estimou-se a correlação momento-produto de Pearson para os animais selecionados em dois diferentes ambientes, de modo a verificar as diferenças de ordenação. As correlações de Pearson estenderam-se de 0,96 a 0,99, sugerindo pequeno ou nenhum efeito da interação genótipo x ambiente nos rebanhos incluídos neste estudo.

The effects of genotype x environment interaction on weaning weight in Nellore cattle were evaluated. A total of 45,697 records of weaning weight adjusted for 205 days obtained from three farms were analyzed. The farms were organized in pairs and analyzed by single-trait analysis, as if they were only one herd. Afterwards, the pairs were submitted to multiple-trait analyses, once the same trait was considered as a distinct trait in each farm. The variance components were estimated by Restricted Maximum Likelihood, using the program MTDFREML. The genetic correlation coefficients varied from 0.79 to 1.00. The Expected Progeny Differences (EPD) were estimated using de same computational program. Later, the sires were organized in accordance with their EPD, selecting the 30 percent best classified sires. Pearson's correlations were estimated among the EPD of animals selected in two different environments, in order to verify changes in their classification. The Pearson's correlations extended from 0.96 to 0.99, suggesting small or inexistent effect of genotype x environment interaction in the herds included in this study.

Genetic analysis of average annual productivity of Nellore breeding cows (COWPROD)

With the aim of estimating the coefficient of heritability of average annual productivity of Nellore cows (COWPROD), a data set from 24,855 animals with known pedigree was analyzed. COWPROD is defined as the amount (in kilograms) of weaned calves produced yearly by one cow during her remaining time in herd ignoring a fixed period of 365 days. COWPROD was calculated regarding three standards: a) based on the post-weaning weight from the calves ignoring any kind of adjustment (COWPROD_NAJ), b) adjusted weight for the fixed effects (COWPROD_AJFIX) and c) adjusted weight for the fixed effects and for the genetic merit of the sire (COWPROD_AJFIN). The obtained heritabilities were 0.15, 0.15 and 0.16 for COWPROD_NAJ, COWPROD_AJFIX and COWPROD_AJFIN, respectively. A complete set composed of 105,158 COWPROD records on 130,740 animals in pedigree was also analyzed for predicting the genetic merit of all animals in the data set and for the calculation of the genetic, phenotypic and residual trends. Ranking correlation was high for the adjusted and non-adjusted data, yet, for some of the animals, the difference among the genetic values was large. This would be an indication that it would be better to work always with the adjusted weaning weights. The genetic trend was positive, but was of small magnitude (0.26% of the trait average) and the residual trend was negative as a consequence of the large intensification of the production system, which has been occurring in the last years in the farms studied. The phenotypic trend was also negative and intermediate between the genetic and the residual ones.

Effects of polymorphisms of LHR and FSHR genes on sexual precocity in a Bos taurus x Bos indicus beef composite population

The purpose of the present research was to investigate the effects of polymorphisms of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) genes, evaluated by polymerase chain reaction-restriction fragment length polymorphism in European-Zebu composite beef heifers from six different breed compositions. The polymorphism site analysis from digestion with HhaI and AluI restriction endonucleases allowed the genotype identification for LHR (TT, CT and CC) and FSHR (GG, CG and CC) genes. A high frequency of heterozygous animals was recorded in all breed compositions for both genes, except in two compositions for LHR. The probability of pregnancy (PP) at first breeding was used to evaluate the polymorphism effect on sexual precocity. The PP was analyzed as a binary trait, with a value of 1 (success) assigned to heifers that were diagnosed pregnant by rectal palpation and a value of 0 (failure) assigned to those that were not pregnant at that time. Heterozygous heifers showed a higher pregnancy rate (67 and 66% for LHR and FSHR genes, respectively), but no significant effects were observed for the genes studied (P = 0.9188 and 0.8831 for LHR and FSHR, respectively) on the PP. These results do not justify the inclusion of LHR and FSHR restriction fragment length polymorphism markers in selection programs for sexual precocity in beef heifers. Nevertheless, these markers make possible the genotype characterization and may be used in additional studies to evaluate the genetic structure in other bovine populations.

Phenotypic and genetic correlations for body structure scores (frame) with productive traits and index for CEIP classification in Nellore beef cattle

The present study was carried out to estimate both (co)variance components and genetic parameters for frame scores obtained using two methods (FRAME_GMA and FRAME_BIF) as well as phenotypic and genetic correlations with traits such as weaning weight, weight gain from weaning to yearling, scrotal circumference, muscle score, and an empiric index for animal classification for the Special Certificate of Identification and Production (CEIP). Data on 12,728 animals, raised in Southeastern Brazil, with ages from 490 to 610 days were analyzed. Estimates of heritability for FRAME_GMA and FRAME_BIF in multi-trait analysis were 0.28 and 0.24, respectively. Genetic correlation coefficients between frame scores and the growth trait were of medium magnitude, which indicates that genetic selection for weight resulted in undesirable responses, increasing the animals’ frames. Small changes should be expected in the frame of animals that have been submitted to a genetic selection regarding muscle score and scrotal circumference. The low magnitude of phenotypic and genetic correlation between frame scores and the empirical selection index that classifies animals for CEIP, a Brazilian official certificate that recognizes the value of seedstock that is not registered at breeders associations, but is genetically evaluated, does not indicate important responses in giving a CEIP to animals that have been directly or indirectly selected for frame. Other studies must be performed to determine estimates of the genetic parameters for frame scores in other beef cattle populations

Genetic parameters for growth traits of a Brazilian Bos taurus x Bos indicus beef composite

The genetic analysis of composite data is very complicated, mainly because it is necessary to adjust data to the effects of heterosis and breed complementarity, and because there is usually considerable confounding of these data with several other effects, such as contemporary group effects, breed composition of the animal and maternal breed composition, among others. Data on birth weight (n = 151,083), weaning weight adjusted to 205 days (n = 137,257), yearling weight adjusted to 390 days (n = 61,410), weight gain from weaning to yearling (n = 56,653), and scrotum circumference (n = 23,323) and muscle score (n = 54,770), both adjusted to 390 days, from Bos taurus x Bos indicus composite beef calves born from 1994 to 2003 were analyzed to estimate (co)variance components and genetic parameters of growth traits. The animals belonged to the Montana Tropical® program. Estimation was made by three models that approach adjustment to heterozygosis in order to suggest the best model. The RM model included contemporary groups, class of age of dam, outcrossing percentages for direct and maternal effects, and direct and maternal additive genetic breed effects as covariates; the R model was the same as RM, but without additive maternal breed effects, and H was the same as RM, but not considering any additive breed effect. Both R2 values and consistency of genetic parameters indicate that the more complex model (RM), which considers maternal and individual additive genetic breed effect, produces the best estimates when compared to other models. The R model seems to overestimate (co)variance components. The magnitudes of direct and maternal heritability estimates, obtained in this study, would permit genetic improvement for weight and growth traits, as much by selection of direct genetic effects for weight and growth as for the improvement of maternal performance, but in different lineages. Therefore, the correlations between these effects were unfavorable.

Genetic trends of absolute and relative heart weight in a male broiler line

Data of chickens from a broiler-breeding program have been collected and used for determination of genetic trends of absolute and relative heart weight. The genetic trends have been estimated by regression of the genetic values of the traits over hatch-year. Genetic values of 42,912 individuals, obtained by restricted maximum likelihood, were used for regression analysis. The estimates of the genetic trends for absolute and relative heart weight were found to be -0.08 g and -0.004% per hatch-year, respectively. These trends show that heart weight in the line analyzed, in absolute and relative terms, has tended to decrease, which can make the metabolic disorders due to the reduction in heart weight in broilers even worse.

Estimativas de adaptabilidade e estabilidade fenotípicas em características produtivas em bovinos de corte mestiços criados em diferentes ambientes / Phenotypic adaptability and stability in productive traits for crossbred beef cattle raised in different environments

Foram analisados 39.212 registros para peso à desmama e 16.546 registros para peso aos 12 meses e ganho de peso até 160 dias pós-desmama, com a finalidade de avaliar a utilização de metodologia para discriminar estimativas de parâmetros de adaptabilidade e estabilidade fenotípicas. Nove composições genotípicas foram distribuídas em seis ambientes para peso à desmama. Para peso aos 12 meses e ganho de peso até 160 dias pós-desmama, utilizaram-se cinco ambientes. As estimativas de médias, desvios-padrão e coeficientes de variação para peso à desmama, peso aos 12 meses e ganho de peso até 160 dias pós-desmama foram: 204,3± 22,6kg e 11,1 por cento; 280,4± 25,9kg e 9,2 por cento e l64,8± 18,1kg e 28,0 por cento, respectivamente. Verificou-se dependência entre principais combinações genotípicas e ambientes avaliados, o que impediu a recomendação geral das melhores combinações genotípicas para todos os ambientes. As análises de adaptabilidade mostraram ser eficientes em discriminar o comportamento das combinações genotípicas dentro de cada ambiente avaliado.

Data from 39,212 weaning weights and 16,546 yearling weights and weight gain from weaning to 160 days after weaning, were used to evaluate a methodology to discriminate estimates of phenotypic adaptability and stability. Nine genotypic compositions distributed in six environments for weaning weight, and in five environments for yearling weight and weight gain from weaning to 160 days post weaning, were analyzed. The averages, standard deviations and coefficients of variation for weaning weight, yearling weight and weight gain from weaning to 160 days post weaning were: 204.3± 22.6kg and 11.1 percent; 280.4± 25.9kg and 9.2 percent; and l64.8± 18.1kg and 28 percent, respectively. The genotype by environment interaction suggests that the best genotype combinations can not be recommended for all the environments. The adaptability analysis was efficient to discriminate genotype combination within environment.

Estimation of genetic parameters for a new model for defining body structure scores (frame scores) in Nellore cattle

Models for estimation of frame scores in Nellore beef cattle (FRAME_GMA) were developed, comparing them with frame scores estimated using equations proposed by the Beef Improvement Federation (FRAME_BIF, USA). Correlation among frame scores obtained by these two methodologies, along with the independent variables considered in the estimation models, were also studied. A data set with 12,728 animals, with ages between 490 and 610 days, was used. The models that best adjusted to FRAME_GMA included hip height, weight and interaction between height and weight. Estimates of heritability for FRAME_GMA and FRAME_BIF were 0.26 +/- 0.03 and 0.23 +/- 0.03, respectively, in single trait analysis, and 0.28 and 0.24, respectively, in multi-trait analysis. Phenotypic Pearson and Spearman correlation coefficients between FRAME_GMA and FRAME_BIF for males were 0.87 and 0.83, respectively, being lower than those found for females (0.92 for both coefficients). Genetic correlation between the frame scores did not differ between genders, with values of 0.92 for the Pearson coefficient and 0.91 for the Spearman coefficient. We concluded that FRAME_GMA was better adapted to this data set than FRAME_BIF. Other studies need to be made to evaluate the applicability of this proposed model to other populations of Nellore beef cattle and for other age groups.

Genetic correlation between heifer pregnancy and scrotal circumference measured at 15 and 18 months of age in Nellore cattle

Data of pregnancy diagnosis from 24,945 Nellore heifers, raised under tropical conditions in Brazil and exposed to breeding at about 14 months of age, were analyzed simultaneously with 13,742 (analysis 1), 36,091 (analysis 2), 8,405 (analysis 3), and 8,405 (analysis 4) scrotal circumference (SC) records of contemporary young bulls in order to estimate heritability (h(2)) for yearling heifer pregnancy (HP) and for SC measured at around 15 (SC15) and 18 (SC18) months of age and to estimate genetic correlation between HP and SC15 (SC18). Heifer pregnancy was considered as a categorical trait, with the value 1 (success) assigned to heifers that were detected as pregnant by rectal palpation approximately 60 days after the end of a 90-day breeding season and the value 0 (failure) otherwise. In analyses 1 and 3, SC was measured at around 15 months of age and in analysis 2 and 4 it was measured at around 18 months of age. Only 8,848 animals from datasets 1 and 2 were common in both files, which means the same animals measured at different ages. Datasets used in analyses 3 and 4 included the same animals, measured at 15 and at 18 months of age, respectively. Heritability estimates for HP were similar in all analyses, with values ranging from 0.66 +/- 0.08 to 0.67 +/- 0.008. For SC15, the estimates were 0.57 +/- 0.05 in analysis 1 and 0.60 +/- 0.07 in analysis 3. For SC18, the estimates were 0.53 +/- 0.03 in analysis 2 and 0.64 +/- 0.06 in analysis 4. The estimates of genetic correlation between HP and SC15 were 0.15 +/- 0.10 in analysis 1 and 0.11 +/- 0.11 in analysis 3. For the correlation between HP and SC18, the values were 0.27 +/- 0.10 in analysis 2 and 0.16 +/- 0.11 in analysis 4. Based on standard errors and confidence intervals, the best heritability and genetic correlation estimates were obtained from analysis 2, which included more data and a better pedigree structure. Pearson correlation between HP and SC breeding values was similar to the gene...

Valores econômicos para habilidade de permanência e probabilidade de prenhez aos 14 meses em bovinos de corte / Economic value for stayability and heifer pregnancy at 14 months in beef cattle herds

Estimaram-se os valores econômicos para as características reprodutivas de probabilidade de prenhez aos 14 meses (PP14) e habilidade de permanência (HP). Foram simulados dados de uma propriedade pecuária de corte, especializada na fase de cria para aplicação de modelagem bioeconômica. A PP 14 foi avaliada considerando taxas percentuais crescentes de prenhez de novilhas aos 14 meses de idade, e a HP foi avaliada a partir da diminuição da taxa de descarte de vacas. O valor econômico da PP 14 foi estimado em R$695,97 por unidade percentual de prenhez de novilhas aos 14 meses, avaliada para o sistema produtivo, enquanto o valor econômico da HP variou em função do custo de compra da novilha de reposição. Os valores, avaliados por unidade percentual de diminuição na taxa de descarte de vacas, foram de R$-2.l40,00, R$-140,00 e R$2.860,00 para o custo de compra da novilha de R$500,00, R$700,00 e R$1.000,00, respectivamente. Os valores econômicos negativos para HP indicaram que o valor de descarte da vaca superou o custo de compra da novilha. Quanto maior for o valor investido na reposição de novilhas maior será a importância econômica do HP.

Genetic characterization of European-Zebu composite bovine using RFLP markers

A population of 370 European-Zebu composite beef heifers, consisting of six different breed compositions (A-F), were characterized genetically, using RFLP markers of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) genes. Our objectives were to genetically characterize this population and to determine the structure and the genetic variability of this hybrid herd. The genotypes were determined through PCR, followed by digestion with restriction endonucleases. The PCR-RFLP analysis made it possible to identify the LHR and FSHR genotypes, as well as to characterize the degree of heterozygosis, which was high for all of the breed compositions, for both loci, except for two combinations for LHR (B and C). The observed heterozygosity (Ho) was lower than the expected heterozygosity (He) for compositions C (for LHR) and A and D (for FSHR); however, for the population as a whole, Ho was above He (with a mean of 57 versus 46%, respectively), reflecting the elevated genetic variability in this population and also the informative value of the RFLP markers, which could be useful for population genetic characterization studies. The analysis of the degree of genetic structure of this population, estimated by the Nei's statistic, for both loci, indicated an elevated total genetic diversity (HT = 47%), with most of this variability being due to intrapopulational diversity (HS = 46%), with a low degree of genetic differentiation among the six breed compositions (GST = 1.2%). The estimates generated by the Wright's F statistic indicated a non-endogamic population, with excess heterozygotes (FIT = -0.22), which was also observed at the intrapopulational level (FIS = -0.23). The results gave evidence that the genetic selection applied to this European-Zebu composite population did not affect the expected high genetic variability for this type of crossbreeding, which makes it possible to use these animals to obtain economically valuable productiv...

Genetic trends of abdominal fat content in a male broiler chicken line

Data of chickens from a broiler-breeding program were collected and used to determine the genetic trends of absolute and relative abdominal fat content. The genetic trends were estimated by the regression of trait genetic value averages on hatch-years. Genetic values from 32,485 individuals were used for regression analysis. The genetic trend estimate for absolute abdominal fat content was +0.39 g per year, indicating that abdominal fat deposition in the analyzed line, in absolute terms, tended to increase, making the existing excess fat deposition in the broilers even worse. However, the genetic trend of relative abdominal fat content was not significant, indicating that there is no increase on abdominal fat content when it is corrected for body weight.

Parâmetros genéticos para escore de umbigo e características de produção em bovinos da raça Nelore / Genetics parameters for umbilicus score and production characteristics in Nellore breed beef cattle

Utilizaram-se 11.310 medidas de escore visual da característica umbigo, medida aos 18 meses em bovinos, para estimar os componentes de variância, a herdabilidade e as correlações genéticas entre escore do umbigo e peso à desmama (PD) e ganho de peso da desmama ao sobreano (GP345), utilizando-se modelo animal bi-característica. Os escores de umbigo (EU) variaram de 1 (mais pendulosos) a 5 (mais curtos). Os valores de herdabilidade foram 0,31 (PD), 0,14 (GP345) e 0,29 (EU), e as correlações genéticas foram -0,05 (EUIPD) e 0,14 (EUIGP345). A correlação entre avaliação do umbigo de machos e fêmeas foi de 0,80. Conclui-se que a característica umbigo é passível de seleção e que ela não compromete a seleção para melhores PD e GP345.

Análise genética de algumas características reprodutivas e suas relaçöes com o desempenho ponderal na raça Nelore / Genetic analysis of some reproductive traits and their relationships with weight traits in Nellore cattle

Com o objetivo de estudar as características idade ao primeiro parto de fêmeas expostas pela primeira vez ao touro em torno de 14 meses de idade (IPP14) ou em torno de 26 meses (IPP26), dias para o parto (DPP), duraçäo da gestaçäo (DG) e perímetro escrotal (PE) e suas relaçöes com as características de desempenho ponderal peso ao nascer (PESNAS), peso à desmama (PESDES), peso ao sobreano (PESSOB) e ganho de peso da desmama ao sobreano (GP345) na raça Nelore, foram analisados conjuntos de dados que variaram de 6.030 a 94.637 observaçöes, de acordo com a característica. As análises foram processadas utilizando-se modelos animais bi-características. Os coeficientes de herdabilidade obtidos para características reprodutivs foram: 0,18 (IPP14); 0,02 (IPP26); 0,06 (DPP); 0,26 (DG); e 0,46 (PE). As correlaçöes entre PE e características de desempenho ponderal indicaram que os pesos näo säo antagônicos ao perímetro escrotal. Embora as correlaçöes genéticas entre PESDES e características reprodutivas das fêmeas tenham sido de baixas a moderadas no sentido desfavorável, näo se recomenda aumento no tamanho adulto dos animais nesses rebanhos para evitar o risco de baixo desempenho reprodutivo. As características PESSOB e GP345 näo säo antagônicas à precocidade sexual e à fertilidade das fêmeas, exceto à duraçäo da gestaçäo

Análise genética da idade ao primeiro parto e do perímetro escrotal em bovinos da raça Nelore / Genetic analysis of age at first calving and scrotal circumference in Nellore cattle breed

Com o objetivo de estudar as características idade ao primeiro parto (IPP) e perímetro escrotal (PE) e sua relaçäo com características de desempenho ponderal em um rebanho bovino da raça Nelore, linhagem Lemgruber, analisaram-se 2.796 observaçöes para IPP, 2.746 para PE, 3.657 para peso à desmama e 4.686 para peso ao sobreano. As análises foram processadas utilizando-se de modelos animais bi e tricaracterística (com peso à desmama ou peso ao sobreano como terceira característica). Peso ao sobreano foi incluído como covariável para PE em duas análises, visando ajustar o PE para peso corporal. Os coeficientes de herdabilidade para IPP e PE variaram de 0,09 a 0,10 e de 0,33 a 0,34, respectivamente. A correlaçäo genética entre IPP e PE variou de -0,23 a -0,29. A correlaçäo negativa näo permite descartar a utilizaçäo do perímetro escrotal como critério de seleçäo para precocidade sexual. Análises multicaracterísticas que incluem o peso ao sobreano parecem mais adequadas à avaliaçäo da idade ao primeiro parto e do perímetro escrotal medido aos 18 meses

Parâmetros genéticos e nível de endogamia em bovinos da raça Santa Gertrudis no Brasil

The present study was carried out in order to estimate genetic, phenotypic and environmental parameters, and inbreeding levels of Santa Gertrudis cattle in Brazil. The traits analyzed were birth weight (PN), 120-day weight (P120), weaning weight (PD), one-year weight (PANO) and 18-month weight (PSANO). A total of 12,737 weight records and pedigree informations of 17,184 animals from 10 generations prior to animals with records (total of 29,921 animals in pedigree) were used. Mixed model methodology under animal model was used in the genetic analyses. Average inbreeding level was not high (0.0395). Heritability estimates for all traits varied from moderate to low (PN = 0.16; P120 = 0.06; PD = 0.13; PANO = 0.12; PSANO = 0.12).

O presente trabalho teve o objetivo de estimar os parâmetros genético, fenotípico e de ambiente e do nível de endogamia em bovinos da raça Santa Gertrudis. As características estudadas foram peso ao nascer (PN), peso aos 120 dias de idade (P120), peso à desmama (PD), peso a um ano de idade (PANO) e peso ao sobreano (PSANO). Foram utilizados dados de produção de 12.737 animais e dados de pedigree de 17.184 animais de 10 gerações anteriores aos animais com dados de produção, num total de 29.921 animais. As análises genéticas foram feitas por meio de metodologia de modelos mistos sob modelo animal. A média da endogamia observada não foi elevada (0,0395). As estimativas de herdabilidade para essa população podem ser consideradas de média a baixa magnitude, o que sugere que processos seletivos terão eficiência apenas a longo prazo. As estimativas de herdabilidade dos efeitos genéticos direto foram: PN = 0,16; P120 = 0,06; PD = 0,13; PANO = 0,12; PSANO = 0,12.

Parâmetros genéticos para coelhos da raça Califórnia criados no Brasil / Genetic parameters for Californian rabbits raised in Brazil

Registros de pesos de 3.249 coelhos, nascidos de 1980 a 1996 e, dados de pedigree de 4.857 coelhos da raça Califórnia, criados no Campus da USP de Pirassununga, Säo Paulo, submetidos à seleçäo por três geraçöes, com base em valores genéticos de pesos à desmama (PD) e à 10ª semana de idade (P10) e ganho de peso da desmama até 10 semanas de idade (GPD10), foram analisados pelo método de modelos mistos sob modelos animais para obter estimativas de parâmetros genéticos para as características consideradas como parte do critério de seleçäo. As estimativas do coeficiente de herdabilidade encontradas foram de 0,23 para PD, de 0,44 para P10 e 0,39 para GP10, mostrando ser possível haver ganhos genéticos se aplicados processos seletivos. A correlaçäo genética entre PD e P10 foi de 0,66 e entre PD e GPD10 foi baixa, indicando que as variáveis säo praticamente independentes. A proporçäo da variância fenotípica devida aos efeitos permanentes de ninhada foi importante para todas as características. Os resultados sugerem que a seleçäo para características ponderais pode ser eficiente