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Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học thế giới đề tài: Estimates of direct and maternal covariance functions for growth of Australian beef calves from birth to weaning | 487 Genet Sei. Evol. 33 2001 487-514 INRA EDP Sciences 2001 Original article Estimates of direct and maternal covariance functions for growth of Australian beef calves from birth to weaning Karin Meyer Animal Genetics and Breeding Unit UniversitY of New EnGland Armidale NSW 2351 Australia Received 30 August 2000 accepted 23 April 2001 Abstract - Records for birth and subsequent monthly weights until weaning on beef calves of two breeds in a selection experiment were analysed fitting random regression models. Independent variables were orthogonal Legendre polynomials of age at weighing in days. Orders of polynomial fit up to 6 were considered. Analyses were carried out fitting sets of random regression coefficients due to animals direct and maternal additive genetic and permanent environmental effects with changes in variances due to temporary environmental effects modelled through a variance function estimating up to 67 parameters. Results identified similar patterns of variation for both breeds with maternal effects considerably more important in purebred Polled Herefords than a four-breed synthetic the so-called Wokalups. Conversely repeatabilities were higher for the latter. For both breeds heritabilities decreased after birth being lowest when maternal effects were most important around 100 days of age. Estimates at birth and weaning were consistent with previous univariate results. covariance functions early growth modelling beef cattle maternal effects 1. introduction Random regression RR models and the associated covariance functions CF have been advocated for the analysis of traits measured repeatedly per individual. They facilitate modelling changes in the trait under consideration over time and in its co variance structure. Applications so far have concentrated on the analysis of test day records of dairy cows 4 8 12-14 30 31 34 35 37 39 40 . Other work considered growth and feed intake in pigs 3 36 feed intake and live weights in dairy cattle 41 and .
