Genetic evaluation for persistency of lactation in Holstein cows using a random regression model

Abstract

A model for analyzing test day records including both fixed and random coefficients was applied to the genetic evaluation of first lactation data for Holstein cows. Data comprising 87045 test-day milk yield records from calving between 1997 and 2001 from Holstein herds in 10 regions of the Brazilian state of Minas Gerais. Six persistency of lactation measures were evaluated using breeding values obtained by random regression analyses. The Wilmink function was used to model the additive genetic and permanent environmental effects. Residual variance was constant throughout lactation. Ranking for animals did not change among criteria for persistency measurements, but ranking changes were observed when the estimated breeding value (EBV) for persistency of lactation was contrasted with those estimated for 305-day milk yield (305MY). The rank correlation estimates for persistency of lactation and 305MY were practically the same for sire and cows, and ranged from -0.45 to 0.69. The EBVs for milk yield during lactation for sires producing daughters with superior 305MY indicate genetic differences between sires regarding their ability to transmit desirable persistency of lactation traits. This suggests that selection for total lactation milk yield does not identify sires or cows that are genetically superior in regard to persistency of lactation. Genetic evaluation for persistency of lactation is important for improving the efficiency of the milk production capacity of Holstein cows.

Genetic relationship of lactation persistency with milk yield, somatic cell score, reproductive traits, and longevity in Slovak Holstein cattle

“…The formulation of persistency better describes the start of lactation. Estimated correlations were similar in sign but different in magnitude compared to the results of Cobuci et al (2007), who reported lower genetic correlations for persistency with a 305-day milk yield (−0.45), similar to Kheirabadi and Alijani (2014) On the contrary, Yamazaki et al (2014a) found positive genetic correlations over the first three lactations (0.48, 0.41, and 0.41). The relationship between 305-day milk yield and persistency was confirmed also by Cobuci et al (2007) and Boujenane and Hilal (2012), with values of r g = 0.49 and r g = 0.89, respectively.…”

Estimativas de parâmetros genéticos para produção de leite e persistência da lactação em vacas Gir, aplicando modelos de regressão aleatória

“…É necessário, portanto, considerar uma estrutura de variâncias heterogêneas para o resíduo, uma vez que as variâncias mostraram comportamento diferenciado no decorrer da lactação. Do mesmo modo, Cobuci et al (2007) Das duas funções de regressão paramétricas usadas neste estudo (Tabela 2), de acordo com os valores do Log L e pelos testes AIC e BIC, a AS foi superior à de WIL, o que pode ser explicado pelo maior número de parâmetros desta função em comparação à de WIL. Assim, de acordo com os critérios avaliados, o melhor modelo para explicar as trajetórias genética e de ambiente permanente, seria o AS, associado a uma estrutura de variâncias residuais, com quatro classes heterogêneas.…”

Genetic Parameters for Milk Yield and Persistency in Carora Dairy Cattle Breed Using Random Regression Model

“…In this way it was possible to estimate the day of maximum production for each lactation. Five measures of PS of lactation were calculated using the results of the RRM, adapting the equations of Jamrozik et al (1997), Jakobsen et al (2002) and Cobuci et al (2004) to the Carora dataset, setting the peak to 50 days of lactation instead of 60. The equations for PS are reported below:…”