Estudo genético e quantitativo da contagem de células somáticas em bubalinos leiteiros
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Data
2007-11-05
Autores
Mendoza-Sánchez, Geovanny [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Considerando-se que a contagem de células somáticas (CCS) de amostras de leite é um valioso indicador da saúde do úbere de búfalas, foi desenvolvido este trabalho com o objetivo de estimar a relação existente entre a CCS e a produção de leite (PL). Foram analisadas informações de 9404 amostras de controles de CCS e PL, referentes a 2198 lactações de animais da raça Murrah com idades entre 2 e 15 anos, filhas de 187 reprodutores, que ocorreram entre os anos 1997 e 2005. Para quantificar as perdas de PL em relação à CCS, nas análises de variância para a variável PL, foram incluídos no modelo os efeitos fixos de fazenda, ordem e ano de parto e estação do parto o escore da contagem de células somáticas (ECCS) como covariável, o efeito de animal dentro da fazenda foi considerado como aleatório. Para a estimação de parâmetros genéticos para a CCS, utilizaram-se “test day models”, a média da contagem de células somáticas na lactação (CCSt270) e a produção de leite aos 270 dias (PL270); os componentes de (co) variância foram estimados usando método de máxima verossimilhança restrita. A CCS de cada mês da lactação foi considerada como uma característica distinta, em análises uni e bicaracterísticas, o modelo incluiu como efeitos aleatórios, o genético aditivo direto e de ambiente permanente e residual. Além disso, foram considerados como efeitos fixos: grupo de contemporâneos, número de controle e idade da vaca ao parto como covariável (efeito linear e quadrático). Para a CCSt nos diferentes meses, os grupos de contemporâneos foram definidos como...
Considering that the somatic cells count (SCC) of samples of milk is a valuable indicator of the health of the buffaloes’ udder, this work was developed with the objective of estimating the relationship between SCC and milk yield (MY). Information on 9404 SCC and MY controls were analyzed. Data contained 2198 lactations of Murrah animals aging between 2 and 15 years, daughters of 187 sires, from 1997 and 2005. To quantify the decreases of MY in relation to SCC, the analyses of variance for the variable MY, included in the model a random animal effect nested in farm and the fixed effects of farm, order and year of parity and season of parity, somatic cells count score (SCCE) as covariate. For estimating genetic parameters for SCC, “test day models were used. For average of somatic cells count in the lactation (SCCt270) and milk yield to 270 days (MY270); the (co) variance components were estimated using Restricted Maximum Likelihood (MTDFREML). SCCs of every month of lactation were considered as different traits in single and double trait analyses. The model included genetic additive, permanent environmental (for SCCt270 and for MY270) and residual random effects. Other fixed effects were: contemporary group; control number and age of cow at parity as a covariate (linear and quadratic effects). For CCSt, contemporary groups were defined as flock-year-month of the control, and for SCCt270 and MY270 as herd-year- season of the parity. x It was found that all effects influenced the expression of SCCE. For first parity females, no relationship between MY and SCC was found. The results indicated that the largest decreases were observed in females with more than one parity. This category... (Complete abstract click electronic access below)
Considering that the somatic cells count (SCC) of samples of milk is a valuable indicator of the health of the buffaloes’ udder, this work was developed with the objective of estimating the relationship between SCC and milk yield (MY). Information on 9404 SCC and MY controls were analyzed. Data contained 2198 lactations of Murrah animals aging between 2 and 15 years, daughters of 187 sires, from 1997 and 2005. To quantify the decreases of MY in relation to SCC, the analyses of variance for the variable MY, included in the model a random animal effect nested in farm and the fixed effects of farm, order and year of parity and season of parity, somatic cells count score (SCCE) as covariate. For estimating genetic parameters for SCC, “test day models were used. For average of somatic cells count in the lactation (SCCt270) and milk yield to 270 days (MY270); the (co) variance components were estimated using Restricted Maximum Likelihood (MTDFREML). SCCs of every month of lactation were considered as different traits in single and double trait analyses. The model included genetic additive, permanent environmental (for SCCt270 and for MY270) and residual random effects. Other fixed effects were: contemporary group; control number and age of cow at parity as a covariate (linear and quadratic effects). For CCSt, contemporary groups were defined as flock-year-month of the control, and for SCCt270 and MY270 as herd-year- season of the parity. x It was found that all effects influenced the expression of SCCE. For first parity females, no relationship between MY and SCC was found. The results indicated that the largest decreases were observed in females with more than one parity. This category... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Bufalo - Aspectos genéticos, Celulas, Mastite, Células somáticas, Herdabilidade, Componentes de variância, Bubalinos leiteiros, Genetic evaluation, Buffaloes, variance components, Longitudinal data, Heritability, Mastitis
Como citar
MENDOZA-SÁNCHEZ, Geovanny. Estudo genético e quantitativo da contagem de células somáticas em bubalinos leiteiros. 2007. xiii, 72 f. Tese (doutorado) - Universidade Estadual Paulista, Faculdade de Ciências Agrárias e Veterinárias, 2007.