RESPONSE TO SELECTION FOR WEIGHT-PER-DAY-OF-AGE IN RAMBOUILLET AND ROMNELET SHEEP

Abstract

Responses to selection for weight-per-day-of-age (WPDA) to about 170 days in Rambouillet and Romnelet sheep over 5 yr, comprising two generations, were measured by two methods. Correlated responses in weaning weight (WW) at about 100 days, and postweaning gain (PWG) for 70 days were also estimated. The estimates of annual genetic increases in WPDA were quite similar in both breeds and from both methods. The improvements of this trait in Rambouillet and Romnelet were estimated as 9.7 and 6.0 g/yr from method 1, and 9.1 and 7.8 g/yr from method II. Estimates of correlated responses in PWG obtained by both methods and in both breeds were close to expected estimates, but correlated responses in WW appeared to be overestimated. Heritability estimates for WPDA using paternal half-sibs were 0.20 for Rambouillet and 0.18 for Romnelet. All genetic correlations among the three traits were positive. Realized heritabilities for WPDA were 0.28 and 0.20 in Rambouillet and Romnelet by method I, and 0.26 in both breeds by method II.