RESUMO -Foram determinados os componentes de (co)variância para caracteres do período pós-desmama na raça Angus e de covariância com peso ao nascer (PN) e caracteres do período pré-desmama por intermédio de um modelo animal. Utilizaram-se dados de 18.921 animais com registros de peso à desmama e ao sobreano, dos quais 4.452 tinham avaliações completas para escores visuais à desmama e ao sobreano. Registros de PN estavam disponíveis para 11.788 animais. As herdabilidades do ganho de peso pós-desmama (GP205) e dos escores de conformação (CS), precocidade (GS), musculatura (MS) e tamanho (TS) ao sobreano foram de 0,20, 0,19, 0,25, 0,26 e 0,24 respectivamente. As correlações genéticas entre os caracteres estudados foram todas positivas: entre GP205 e escores visuais variaram de 0,50 a 0,71; para os escores ao sobreano entre si, de 0,22 a 0,94; entre GP205 e PN foram de 0,14; entre GP205 e ganho pré-desmama, de 0,23; e para o mesmo escore visual observado à desmama e ao sobreano, de 0,90 a 0,99. Esses resultados indicam que é possível selecionar para GP205, sem aumento importante do PN, e que a seleção para GP205 deverá promover uma mudança genética correlacionada em escores visuais ao sobreano.Palavras-chave: Angus, bovinos de corte, correlação genética, herdabilidade, período pós-desmama (Co)Variance Components and Genetic Parameters of Post-Weaning Traits in Angus CattleABSTRACT -(Co)variance components were determined for post-weaning traits, and covariances with birth weight (BW) and preweaning traits, in Angus cattle using an animal model. Records of weaning and yearling weights of 18,921 animals were used and from these 4,452 had complete evaluations of visual scores at weaning and post-weaning phases. Records of BW were available for 11,788 animals. Heritabilities of post-weaning gain (GP205) and visual scores for conformation (YC), precocity (YP), muscling (YM) and size (YS) were 0.20, 0.19, 0.25, 0.26 and 0.24, respectively. Genetic correlations among all traits considered were positive: between GP205 and visual scores the range was from 0.50 to 0.71; for yearling scores among themselves from 0.22 to 0.94; between GP205 and BW was 0.14; between GP205 and pre-weaning gain was 0.23 and for the same score at weaning and yearling stages they varied from 0.90 to 0.99.These results indicate that it is possible to select for GP205 without a significant increase in BW and that the selection for GP205 should produce a correlated genetic change on yearling visual scores.
RESUMO -Foram estimados componentes de (co)variância e parâmetros genéticos para peso ao nascer (PN), ganho do nascimento à desmama (G205) e escores de conformação (CD), precocidade de terminação (GD), musculatura (MD) e tamanho (TD) à desmama, utilizando-se registros de desmama de 40.915 bezerros Angus, criados no Estado do Rio Grande do Sul, sul do Brasil. Desses, 12.706 tinham pesagem ao nascer e 11.863, avaliação completa para escores visuais (EV). Os dados foram analisados por meio de um modelo animal, em análises uni e multivariadas, e os componentes de variância estimados pela máxima verossimilhança restrita. As herdabilidades aditivas diretas estimadas foram 0,29; 0,25; 0,18; 0,19; 0,19; e 0,21, respectivamente, para PN, G205, CD, GD, MD e TD. A herdabilidade materna para G205 foi 0,16 e a correlação entre efeito genético direto e materno, -0,51. Essa correlação negativa indica antagonismo entre esses efeitos e provocou decréscimo na herdabilidade total para G205, que foi 0,18. A contribuição do ambiente permanente da vaca para a variância fenotípica esteve entre um mínimo de 0,05 para PN e máximo de 0,12 para G205. A correlação genética entre PN e G205 foi -0,06, mostrando que estes caracteres são independentes geneticamente. As correlações genéticas encontradas entre G205 e EV foram entre 0,71 e 0,86 e de EV entre si, 0,58 a 0,91. Essas associações positivas entre os escores visuais e destes com o crescimento na fase pré-desmama favorecem a seleção conjunta destes caracteres, por meio de índices de seleção.Palavras-chave: bovinos de corte, correlações, herdabilidade, modelo animal (Co)Variance Components and Genetic Parameters for Weaning Production Traits of Angus Calves Raised in the State of Rio Grande do SulABSTRACT -(Co) variance components and genetic parameters for birth weight (BW), adjusted weaning gain (AWG) and for conformation (WC), precocity (WP), muscling (WM) and size (WS) scores at weaning were estimated, from records of 40,915 Angus calves, raised in the state of Rio Grande do Sul, southern Brazil. From that data, 12,706 had birth weight records and 11,863 had complete records for visual scores (VS). The data were analyzed using an animal model, in uni and multivariate analyses, and the variance components estimated by restrict maximum likelihood. The direct additive heritabilities estimated were 0.29, 0.25, 0.18, 0.19, 0.19 and 0.21, respectively for BW, AWG, WC, WP, WM and WS. Maternal heritability for AWG was 0.16 and genetic correlation between direct and maternal effects was -0.51. This high negative correlation indicates antagonism between these effects and decreases total heritability for AWG to 0.18. The contribution of dam permanent environment to phenotypic variance was between a minimum of 0.05 for BW and a maximum of 0.12 for AWG. Genetic correlation between BW and AWG was -0.06, showing that these traits are genetically nondependent. The genetic correlations found between AWG and VS were from 0.71 to 0.86, and among VS traits from 0.58 to 0.91. These positive associations ...
RESUMO Para avaliar a influência de alguns fatores de ambiente sobre escores de avaliação visual à desmama em animais da raça Charolês e estimar parâmetros genéticos, foram utilizadas informações coletadas pelo PROMEBO durante os anos de 1994 a 2002. As características estudadas foram os escores de conformação (C), precocidade (P), musculatura (M) e tamanho (T) à desmama
Os objetivos deste estudo foram determinar a importância dos efeitos de idade da vaca (IV), sexo (S) e idade do bezerro (ID), mês de nascimento (M) e a interação entre idade da vaca e sexo (IV*S) sobre escores de avaliação visual (EV) para conformação (CD), precocidade (GD), musculatura (MD) e tamanho (TD) à desmama, de bovinos Angus, e estimar fatores de correção para esses efeitos. Foram utilizados 11.863 registros coletados pelo Programa de Melhoramento de Bovinos de Carne - PROMEBO, durante os anos de 1989 a 1997. Os dados foram analisados por meio do PROC MIXED do SAS. O modelo incluiu os efeitos de grupo de contemporâneos, M, IV, S, ID (linear e quadrático), IV*S e o efeito aleatório do touro. A partir das médias ajustadas de CD, GD, MD e TD, foram estimadas equações de regressão para M e IV*S. Os EV apresentaram resposta aos efeitos de IV, S e ID similar à do ganho de peso na fase de desmama. A idade do bezerro foi o fator responsável pelas maiores variações não-genéticas nos EV. Fatores de correção para ajuste de IV, ID e data juliana do nascimento foram propostos.
Pedigree information available for Angus (ANG), Devon (DEV), Hereford (HER), and Shorthorn (SHO) cattle in Brazil was analyzed to appraise the genetic diversity and population structure of these breeds. Pedigree records collected from the beginning of the 20th century until 2010 were used in the analyses. Over time, the number of herdbook registrations declined in HER after a peak in the 1970s, remained low in DEV and SHO, and increased steadily in ANG since the 1990s, such that it the latter is now the leading British cattle breed in Brazil. The average number of offspring registered per sire ranged from about 12 (SHO) to 20 (DEV) and the mean generation interval ranged from about 6.0 (HER and SHO) to 6.4 (ANG) years. In the reference population (calves born in 2009 and 2010, plus those born in 2008 for SHO) the mean equivalent number of generations known ranged from about 7 (SHO) to 9 (HER). In the 4 breeds studied, nearly all animals born over the last few years are inbred, even though the mean level of inbreeding in the reference population is below 4% in all breeds. The rate of inbreeding per generation, computed from the individual increase in inbreeding, ranged from about 0.2 (ANG) to 0.5% (DEV), with a corresponding effective population size of 245 and 92, respectively, which is above the recommended minimum critical threshold. The number of founders/ancestors contributing with 50% of the reference population gene pool was 211/26 for ANG, 41/14 for DEV, 164/25 for HER, and 79/10 for SHO, with effective number of founders/ancestors/founder genomes of 470/68/36, 89/33/16, 289/59/30, and 200/28/18 for ANG, DEV, HER, and SHO, respectively. The genetic contribution of different countries to the gene pool of each breed indicated that, throughout the period studied, DEV genes originated predominantly from the United Kingdom, while for the other breeds there was a changing pattern over time. Until the 1970s Argentina was the major supplier of ANG, while HER and SHO genes were mostly from Uruguay, but since then the United States took the leading role as supplier of ANG, HER, and SHO genes to Brazil. Our results reveal a mild increase in inbreeding in all breeds studied, with effective population size estimates indicating that reasonable levels of genetic diversity have been maintained in all 4 breeds. Continuous monitoring of inbreeding trends and of parameters derived from probability of gene origin should be ensured to warrant the long-term maintenance of genetic diversity.
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