Changes over time in genetic parameters for growth in bulls and assessment of suitability of test methods

Abstract

Objectives of the study were to examine alternative measures of growth potential of bulls in testing stations, determine whether genetic parameter estimates of such traits changed over time, and examine whether existing methods for performance testing were appropriate. Records from 1980 to 2010 of 44 425 Fleckvieh bulls in Czech progeny testing stations were analyzed. The following traits were examined: weight at the beginning of the test (150 th day of age), weight at the end of the test (530 th day of age), gain from birth to the beginning of the test, and gain during the test. Fixed effects in five multi-trait animal models were stationyear-season groups, linear and quadratic regressions on age, and regression on heterozygosity (proportion of an individual's loci with alleles from different ancestor breeds). Random effects included additive genetic, permanent environment, and residual variances. Separate analyses were conducted in four consecutive time periods (1980-1987, 1988-1992, 1993-1997, and 1998-2010). Across these time intervals, estimates of additive genetic variance decreased for all of the traits, while estimates of residual variances increased. In consequence, heritability estimates for all of the traits decreased over time. This decrease was most apparent for gain during the test, for which heritability declined by more than 50% over the course of the study. Results demonstrate that over three decades, the system of testing came into conflict with genetic improvement of the breed, possibly because the measured traits changed genetically over the course of selection. Regular analysis of the recorded data, re-estimation of genetic parameters in relation to time, and appropriate modification of existing methods of rearing/fattening in station tests are required. When such inspections are neglected, data from the testing stations may not accurately reflect genetic merit of individual animals.

Environmental Factors and Genetic Parameters of Beef Traits in Fleckvieh Cattle Using Field and Station Testing

“…The FAT percentage (b = 0.0018 and 0.0004, respectively) increases with growing age and MUS (b = 0.0218) also improves slightly. The age at slaughter is given as a statistically significant factor by a number of authors, e.g., [ 14 , 15 , 20 ]. According to these authors, both the carcass weight and fatness increase with growing age [ 14 ].…”

“…This effect, similarly to the assessment of milk yield, explains a significant part of the variability since it includes the rearing environment, nutrition and seasonality. The conclusive influence of the season and year of birth on meat yield indicators is stated by [ 15 ]. The conclusive influence of the herd, year of birth and season on selected meat yield traits is also stated for various breeds [ 14 , 27 ].…”

“…A heritability for FAT of 0.35 and 0.50 for CW is described for Korean Brindle Cattle [14]. In the case of cattle reared in the Czech Republic, h 2 values range from 0.20 to 0.35 for body weight (BW) [15]. Moderately high h 2 for CW and moderately low for DP are reported by [31].…”

“…A number of authors [ 11 , 12 , 13 , 14 ] pursued the links between meat yield indicators, particularly genetic correlation, in great detail. For example, [ 15 ] discussed the estimates of genetic parameters in Fleckvieh. The influence of various environmental factors and the type of fattening system (organic farming for instance) was discussed by [ 16 ].…”

Genetic Variance Estimation over Time in Broiler Breeding Programmes for Growth and Reproductive Traits

“…Nevertheless, apart from the HHP variance of the first window, all expected variances are lower than the estimated genetic variance and the variance of the base population. Reports of genetic variance reduction have been observed in commercial pigs [11], Czech Fleckvieh dual-purpose cattle [46] for growth traits, and in dairy sheep for milk production [12]. In the case of the sheep program, estimates indicated a 10% loss of genetic variance due to the Bulmer effect and preselection pressure at birth (selection) [12].…”