Selection Indices for The Friesian Heifers' Weights in Libya

Abstract

This study constructed restricted, multi source, and desired gain selection indices for two growth traits – birth weight (BW) and weight at service (WS) – using data from 548 female Friesian heifers that had complete records for both traits at alnasir project in period(1983-1994) . Economic values were derived by the Beta regression method with the goal of improving WS while restricting BW (a_WS = 1, a_BW = 0). Eight indices were constructed: general (I1), partial restriction on BW at 25 % (I2), 50 % (I3), 75 % (I4), complete restriction (I5), multi source (I6), and two desired gain indices (I7), (I8). The general index gave an accuracy (RIh) of 0.464. Partial restriction at 75 % (I4) maintained good accuracy (RIh = 0.417, RE = 89.9 %) and limited BW increase to 0.59 kg/generation. Complete restriction (I5) reduced accuracy to 0.320 (RE = 69.0 %). The multi source index achieved the highest accuracy (RIh = 0.501, RE = 108.0 %). Desired gain indices achieved specified targets in about one generation at i = 1. It is recommended to use partially restricted indices when BW is near its optimum, and multi source or desired gain indices when higher accuracy or specific targets are needed.