Estimation of genetic parameters for electrical conductivity of milk for Holstein breed using random regression / Estimativa de parâmetros genéticos para condutividade elétrica do leite para a raça holandesa utilizando regressão aleatória

The electrical conductivity of milk is an indirect method of mastitis diagnosis and can be used as selection criterion in breeding programs to obtain resistant animals to infection. For the present study data from 9,302 milk electrical conductivity measurements in the morning (ECM), from 1,129 Holstein cows in first lactation, calving between 2001 and 2011, belonging to eight herds in the Southeast of Brazil, obtained from automated milking equipment WESTFALIA® with system management "Dairyplan" was utilized. Classes of ECM were formed at weekly intervals, representing a total of 42 classes. The model included direct additive genetic, permanent environmental and residual effects as random and the fixed effects of contemporary group (herd - year and season of the control), age at calving as a covariate (linear and quadratic). Mean trends were modeled by an orthogonal Legendre polynomial with three coefficients of days in milk. The residual variance was considered homogeneous throughout lactation. Variance components were estimated by restricted maximum likelihood method (REML), using the statistical package Wombat (Meyer, 2006). The mean and standard deviation of the electrical conductivity of milk were 4.799 ± 0.543 ms/cm. The heritability for ECM were increased from the beginning to the middle of lactation (154 days), when it reached the maximum value (0.44), decreasing therea

O artigo não apresenta resumo em português.

Genetic parameters for longevity in Holteins cows / Parâmetros genéticos para longevidade em vacas da raça Holandesa

The milk yield has been the most selected trait in dairy cattle breeding programs. However various studies have shown a decline in adaptive and longevity traits in herds that are under selection for improving production, especially in taurine breeds, as the Holstein, who was highly selected for milk production. The aim of this study was to estimate genetic parameters for first lactation 305-day milk yield (Y305) and for longevity traits and to verify the association among them, in high production Holstein cows. The data sets used were from Agrindus Farm, with calving occurring between 1989 and 2005. The traits analyzed were Y305, productive life (PL), calculated as the length of lactation days from the first day of lactation until the culling, and age at culling (AC). Variance components were estimated by Restricted Maximum Likelihood, applying multi-trait animal model. Heritability estimates for Y305, PL and AC were, respectively, 0.35, 0.07 and 0.10. Heritability estimates for PL and AC suggest small genetic variability to get genetic gains by direct selection for these traits, because they are influenced by decisions of voluntary and involuntary culling, being largely affected by factors related to the environment. It is difficult to measure these traits because it is necessary to evaluate culling of animals and causes of culling. The magnitude of the heritability estimate f

O artigo não apresenta resumo em português.

Modelos de dimensão finita para a estimação de parâmetros genéticos para a produção de leite de primeiras lactações de vacas da raça Holandesa

Genetic parameters for 50,171 first lactation test-day milk yields and 305 day milk yield (Y305) of 9,281 Holstein cows were estimated, applying uni and bi-trait animal models. The model for Y305 included the additive genetic effect as random and the fixed effects of contemporary group and age of cow at calving as covariable. For TDMY the same animal model described for Y305 was used, including days in milk as covariable. Variance components were estimated by Restricted Maximum Likelihood. Heritability estimates obtained for TDMY ranged from 0.07 to 0.19 and from 0.12 to 0.22 by uni-trait and bi-trait analysis, respectively. Heritability for Y305 was 0.26 by uni-trait and 0.27 by bi-trait analysis. The genetic correlations between TDMY and Y305 were all positive and high, ranging from 0.63 to 1.00. The genetic correlations between TDMY ranged from 0.30 to 1.00. Selection for Y305 seems to be the best selection criterion to be adopted, since it provides larger genetic gain for milk productions in, practically, all test days.

Foram estimados parâmetros genéticos para produção de leite acumulada até 305 dias (P305) e produção de leite no dia do controle (PLDC) de 50.171 controles mensais de 9.281 primeiras lactações de vacas da raça Holandesa. A P305 e as PLDC foram analisadas por meio de modelo animal uni e bicaracterísticas. Para a P305 o modelo incluiu como aleatório, o efeito genético e como efeitos fixos o grupo de contemporâneos e a covariável idade da vaca ao parto. Para as PLDC foi usado o mesmo modelo descrito para a P305, incluindo como covariável o número de dias em lactação. Os componentes de variância foram estimados pelo Método da Máxima Verossimilhança Restrita. As estimativas de herdabilidade (h²) para as PLDC oscilaram entre 0,07 e 0,19 em análises unicaracterísticas e, de 0,12 a 0,22 nas bicaracterísticas. Para a P305, as h² resultantes das análises uni-característica e bicaracterística foram 0,26 e 0,27, respectivamente. As correlações genéticas das PLDC com a P305 foram todas positivas e elevadas, variando de 0,63 a 1,00. As correlações genéticas entre as PLDC variaram de 0,30 a 1,00. A seleção para a P305 parece ser o melhor critério de seleção a ser adotado, uma vez que proporciona maiores ganhos genéticos para as produções de leite em, praticamente, todos os controles da lactação.

Modelos de dimensão finita para a estimação de parâmetros genéticos para a produção de leite de primeiras lactações de vacas da raça Holandesa

Genetic parameters for 50,171 first lactation test-day milk yields and 305 day milk yield (Y305) of 9,281 Holstein cows were estimated, applying uni and bi-trait animal models. The model for Y305 included the additive genetic effect as random and the fixed effects of contemporary group and age of cow at calving as covariable. For TDMY the same animal model described for Y305 was used, including days in milk as covariable. Variance components were estimated by Restricted Maximum Likelihood. Heritability estimates obtained for TDMY ranged from 0.07 to 0.19 and from 0.12 to 0.22 by uni-trait and bi-trait analysis, respectively. Heritability for Y305 was 0.26 by uni-trait and 0.27 by bi-trait analysis. The genetic correlations between TDMY and Y305 were all positive and high, ranging from 0.63 to 1.00. The genetic correlations between TDMY ranged from 0.30 to 1.00. Selection for Y305 seems to be the best selection criterion to be adopted, since it provides larger genetic gain for milk productions in, practically, all test days.

Foram estimados parâmetros genéticos para produção de leite acumulada até 305 dias (P305) e produção de leite no dia do controle (PLDC) de 50.171 controles mensais de 9.281 primeiras lactações de vacas da raça Holandesa. A P305 e as PLDC foram analisadas por meio de modelo animal uni e bicaracterísticas. Para a P305 o modelo incluiu como aleatório, o efeito genético e como efeitos fixos o grupo de contemporâneos e a covariável idade da vaca ao parto. Para as PLDC foi usado o mesmo modelo descrito para a P305, incluindo como covariável o número de dias em lactação. Os componentes de variância foram estimados pelo Método da Máxima Verossimilhança Restrita. As estimativas de herdabilidade (h²) para as PLDC oscilaram entre 0,07 e 0,19 em análises unicaracterísticas e, de 0,12 a 0,22 nas bicaracterísticas. Para a P305, as h² resultantes das análises uni-característica e bicaracterística foram 0,26 e 0,27, respectivamente. As correlações genéticas das PLDC com a P305 foram todas positivas e elevadas, variando de 0,63 a 1,00. As correlações genéticas entre as PLDC variaram de 0,30 a 1,00. A seleção para a P305 parece ser o melhor critério de seleção a ser adotado, uma vez que proporciona maiores ganhos genéticos para as produções de leite em, praticamente, todos os controles da lactação.

Alternative analysis for the study of subsequent breeding in Nelore heifers / Análises alternativas no estudo da reconcepção de novilhas Nelore

Data of 1727 Nelore heifers born from 1993 to 1999 were analyzed in order to compare heritability estimate values of subsequent rebreeding (SR) using linear and non-linear models. SR was defined as the observation of two years old heifers conceiving and remaining pregnant to palpation, given a previous pregnancy around 14 months and exposure during the breeding season. Restricted maximum likelihood (REML) and Bayesian inference were used to estimate variance components for linear and non-linear models. These models included contemporary group and service period as fixed effects and animal and residual as random effects. Heritability estimates from linear models were from 0.05 and 0.11, and the higher values were obtained after transformed them to an underlying normal scale. The heritability estimate obtained using non linear model was even higher (0.16). The inclusion of heifer subsequent rebreeding trait in the selection indexes of Nelore cattle can contribute to increase the fertility of the herds.

Dados de 1727 fêmeas primíparas da raça Nelore, nascidas entre 1993 e 1999, foram utilizados com o objetivo de comparar os valores das estimativas de herdabilidade da característica reconcepção (REC), utilizando-se os modelos linear e não linear. As fêmeas foram expostas aos touros pela primeira vez em torno de 14 meses de idade, sendo consideradas para a característica REC aquelas que pariram e entraram na segunda estação de monta. Os efeitos considerados nos modelos foram: grupo de contemporâneo (fazenda, ano e mês de nascimento) e período de descanso como efeitos fixos, além do animal e resíduo como efeitos aleatórios. Foram usadas as metodologias de máxima verossimilhança restrita (REML) e inferência bayesiana para estimar os componentes de variância, por modelo linear e não linear, respectivamente. As estimativas de herdabilidade utilizando-se modelo linear ficaram entre 0,05 a 0,11 sendo as superiores obtidas após a transformação da estimativa para a escala normal subjacente. A estimativa de herdabilidade obtida utilizando-se modelo não linear foi superior (0,16). A inclusão da característica reconcepção de novilhas nos índices de seleção de bovinos Nelore pode contribuir para o aumento da fertilidade dos rebanhos.

Alternative analysis for the study of subsequent breeding in Nelore heifers / Análises alternativas no estudo da reconcepção de novilhas Nelore

Data of 1727 Nelore heifers born from 1993 to 1999 were analyzed in order to compare heritability estimate values of subsequent rebreeding (SR) using linear and non-linear models. SR was defined as the observation of two years old heifers conceiving and remaining pregnant to palpation, given a previous pregnancy around 14 months and exposure during the breeding season. Restricted maximum likelihood (REML) and Bayesian inference were used to estimate variance components for linear and non-linear models. These models included contemporary group and service period as fixed effects and animal and residual as random effects. Heritability estimates from linear models were from 0.05 and 0.11, and the higher values were obtained after transformed them to an underlying normal scale. The heritability estimate obtained using non linear model was even higher (0.16). The inclusion of heifer subsequent rebreeding trait in the selection indexes of Nelore cattle can contribute to increase the fertility of the herds.

Dados de 1727 fêmeas primíparas da raça Nelore, nascidas entre 1993 e 1999, foram utilizados com o objetivo de comparar os valores das estimativas de herdabilidade da característica reconcepção (REC), utilizando-se os modelos linear e não linear. As fêmeas foram expostas aos touros pela primeira vez em torno de 14 meses de idade, sendo consideradas para a característica REC aquelas que pariram e entraram na segunda estação de monta. Os efeitos considerados nos modelos foram: grupo de contemporâneo (fazenda, ano e mês de nascimento) e período de descanso como efeitos fixos, além do animal e resíduo como efeitos aleatórios. Foram usadas as metodologias de máxima verossimilhança restrita (REML) e inferência bayesiana para estimar os componentes de variância, por modelo linear e não linear, respectivamente. As estimativas de herdabilidade utilizando-se modelo linear ficaram entre 0,05 a 0,11 sendo as superiores obtidas após a transformação da estimativa para a escala normal subjacente. A estimativa de herdabilidade obtida utilizando-se modelo não linear foi superior (0,16). A inclusão da característica reconcepção de novilhas nos índices de seleção de bovinos Nelore pode contribuir para o aumento da fertilidade dos rebanhos.

Genetic parameters for longevity in Holteins cows / Parâmetros genéticos para longevidade em vacas da raça Holandesa

The milk yield has been the most selected trait in dairy cattle breeding programs. However various studies have shown a decline in adaptive and longevity traits in herds that are under selection for improving production, especially in taurine breeds, as the Holstein, who was highly selected for milk production. The aim of this study was to estimate genetic parameters for first lactation 305-day milk yield (Y305) and for longevity traits and to verify the association among them, in high production Holstein cows. The data sets used were from Agrindus Farm, with calving occurring between 1989 and 2005. The traits analyzed were Y305, productive life (PL), calculated as the length of lactation days from the first day of lactation until the culling, and age at culling (AC). Variance components were estimated by Restricted Maximum Likelihood, applying multi-trait animal model. Heritability estimates for Y305, PL and AC were, respectively, 0.35, 0.07 and 0.10. Heritability estimates for PL and AC suggest small genetic variability to get genetic gains by direct selection for these traits, because they are influenced by decisions of voluntary and involuntary culling, being largely affected by factors related to the environment. It is difficult to measure these traits because it is necessary to evaluate culling of animals and causes of culling. The magnitude of the heritability estimate f

O artigo não apresenta resumo em português.

Occurrence of clinical mastitis and environmental factors favoring its incidence / Ocorrência da mastite clínica e fatores ambientais que favorecem sua incidência

The objective of this study was to evaluate the frequency of clinical mastitis (CM), in high production Holstein cows, as well as the environmental factors that favoring its incidence. The average milk production of 305 days, according to the class of mastitis was estimated by the method of least squares. The frequencies of clinical mastitis (CM) events were analyzed according to the calving sequences (1-6), year of calving, season and stage of lactation, and infected quarter (right anterior, left anterior, right posterior, left posterior). The frequency of CM ranged from 11.39% in the first calving to 21.18% in the third. 58.56% of mastitis cases occurred in the wet season, and 41.44% occurred in the dry season. The final lactation stage (200 to 300 days) was the period with the highest occurrence of CM (45.33%). The quarter posterior had a higher frequency CM (54.25%). Animals with higher levels of milk production of 305 days showed highest occurrence of CM. We must find a balance between milk production and mastitis in order to increase profitability. The study of the periods of greatest frequency clinical mastitis events is essential for dairy farming, to direct a program to control this disease.

O objetivo deste estudo foi verificar as frequências de mastite clínica (MC) em vacas Holandesas de alta produção de leite, bem como os fatores ambientais que influenciam sua incidência. A média da produção de leite aos 305 dias de acordo com a classe de mastite foi estimada pelo método de quadrados mínimos. As frequências de MC foram analisadas de acordo com as ordens do parto (1 a 6), ano do parto, estação do ano, fase da lactação, e quarto infectado (anterior direito, anterior esquerdo, posterior direito, posterior esquerdo). A frequência da MC por ordem de parto variou de 11,39% no primeiro parto a 21,18% no terceiro parto. 58,56 % dos casos de mastite ocorreram no período das águas e 41,44% no período da seca. O terço final da lactação foi o período com maior ocorrência de casos de MC (45,33%). Os quartos posteriores apresentaram maior frequência de MC (54,25%). Os animais com maiores níveis de produção de leite aos 305 dias (9.466,42 Kg) foram os que apresentaram maior incidência de mastite clínica. Deve-se encontrar um ponto de equilíbrio entre a produção de leite e a mastite a fim de aumentar a rentabilidade da produção. O estudo dos períodos de maior frequência de ocorrência de mastite clínica é fundamental para a pecuária leiteira, para o direcionamento de um programa de controle dessa doença.

Estimation of genetic parameters for electrical conductivity of milk for Holstein breed using random regression / Estimativa de parâmetros genéticos para condutividade elétrica do leite para a raça holandesa utilizando regressão aleatória

The electrical conductivity of milk is an indirect method of mastitis diagnosis and can be used as selection criterion in breeding programs to obtain resistant animals to infection. For the present study data from 9,302 milk electrical conductivity measurements in the morning (ECM), from 1,129 Holstein cows in first lactation, calving between 2001 and 2011, belonging to eight herds in the Southeast of Brazil, obtained from automated milking equipment WESTFALIA® with system management "Dairyplan" was utilized. Classes of ECM were formed at weekly intervals, representing a total of 42 classes. The model included direct additive genetic, permanent environmental and residual effects as random and the fixed effects of contemporary group (herd - year and season of the control), age at calving as a covariate (linear and quadratic). Mean trends were modeled by an orthogonal Legendre polynomial with three coefficients of days in milk. The residual variance was considered homogeneous throughout lactation. Variance components were estimated by restricted maximum likelihood method (REML), using the statistical package Wombat (Meyer, 2006). The mean and standard deviation of the electrical conductivity of milk were 4.799 ± 0.543 ms/cm. The heritability for ECM were increased from the beginning to the middle of lactation (154 days), when it reached the maximum value (0.44), decreasing therea

O artigo não apresenta resumo em português.