Models for evaluation of growth of performance tested bulls
J. Přibyl, H. Krejčová, J. Přibylova, I. Misztal, S. Tsuruta, N. Mielenzhttps://doi.org/10.17221/331-CJASCitation:Přibyl J., Krejčová H., Přibylova J., Misztal I., Tsuruta S., Mielenz N. (2008): Models for evaluation of growth of performance tested bulls. Czech J. Anim. Sci., 53: 45-54.
Before being used for insemination, young bulls of Czech Fleckvieh (CF) are tested for growth at performance-test stations. While at stations, the bulls are weighed monthly. Evaluation included 7 448 bulls with 82 676 records of weight measured from 6 to 520 days of life. In the station-year-period (HYS), which can be prolonged up to 3 months, different groups were tested according to the beginning of growth curve and according to test-days of weighing. Weight analyses were used to handle heterogeneous variability based on age. Legendre Polynomials (LP) with 5 parameters described the average growth curve for HYS classes. Deviations from average curves were decomposed into genetic (G), animal’s permanent environment (PE) and residual (RES) components. Functions of (G) and (PE) were tested using LP random regression (RR) methodology with 5 or 3 parameters and Linear Spline (SP) function with 5 knots. Variance increases with the age of the animals. From 100 to 400 days, heritability was nearly the same with a mild depression in the middle of the period. The average was h2 = 0.31 and ended with h2 = 0.36. Results were similar for variance components, heritability, genetic, environmental and phenotype correlations from different models with different LP and SP functions. Higher RES variability occurred only for LP with 3 parameters. For traits like live weight, the RR should have at least 3 parameters and SP function should be used.Keywords:cattle; random regression; heritability; statistical model; growth curve; bulls