some considerations on selection criteria and optimization for terminal sire breeds一些因素选择标准及优化终端陛下品种.pdf

REVIEW SOME CONSIDERATIONS ON SELECTION CRITERIA AND OPTIMIZATION FOR TERMINAL SIRE BREEDS 1)( J. L. FOULLEY Station de Génétique quantitative et appliquee, Centre national de Recherches zootechniques, I. N. R. A.,., 78350 Jouy en Josas SUMMARY The efficiency of selection of beef breeds for terminal crossing has been analysed in terms of selection criteria for growth and methods for selection of sires, notably with reference to the situation and research in France. With respect to selection of specialized beef lines, the advantage of control of the individual feed intake and of carcass performances as compared to control of growth only is shortly discussed. For this purpose, not only the favourable indirect response but also the resulting increment of feed intake and changes in body composition according to the reference system used (weight, duration, age) should be taken into account. Because of the increase in birth weight due to the intensification of selection for muscle growth within the beef breeds and the strong genetic correlation between this weight and the paternal component of calving difficulties, it seems advisable to use restricted indices for selection on birth weight, at least for terminal sire lines used in heifers. In the French situation of terminal crossing practised on suckling cows of dual purpose or hardy breeds with the aim of producing veal calves, a special attention has been paid to the genetic and economic advantage of two stage selection for choosing bull sires : selection on a sta- tion performance test selection on a field test -month-weight).3(