Days to Calving of Nelore Cows from a Selection Experiment for Growth: II - Random Regression Model

[摘要] - Genetic parameters for days to calving were estimated using a random regression model, with orthogonal polynomials of age at breeding season (in years) as covariable. The records of days to calving (4,118) came from 929 cows from three experimental Nelore herds, been the selection and traditional herds selected for higher yearling weight and the control herd selected for the mean of yearling weight. Genetic and permanent environmental variances were described by a fourth order polynomial function, with 9 measures of error. The phenotypic and additive genetic variances were high in late records, especially after the 6th breeding season. Heritabilities estimates increased from 0.08 to 0.28, from first up to 6th breeding season. Genetic correlations were moderate between the first and the later records (0.32 to 0.66), high between adjacent records (0.98 to 0.99), and a little smaller between non adjacent records (0.63 to 0.98). The selection for weight did not alter the average breeding value of cows of selection herds, however the average genetic breeding values of control cows declined through the years.

[学科分类] 兽医学

[关键词] reproductive performance;beef cattle;repeated records;covariance functions    Introdução A Estação Experimental de Zootecnia de Sertãozinho (São Paulo;Brasil) iniciou em 1976 um experimento de seleção com animais Nelore a fim de examinar a resposta à seleção para peso corporal em genótipos de interesse nos trópicos;já que os poucos experimentos de seleção no mundo eram com raças européias