Possible correlated or pleiotropic effects on food intake, growth rate and carcass traits (meat quality and carcass composition traits) were investigated for the prolificacy related Booroola gene (FecB
). This gene was introgressed in a Texel sheep population by systematic backcrossing with sires carrying the Booroola gene. In a 3-year experiment 273 spring-born male lambs were offered concentrates ad libitum, after weaning. Lamb carrier effects and dam carrier effects for the FecB
gene were estimated, accounting for year, backcross generation, slaughter weight, weaning age, concentrate type, rearing code, age of the dam and litter size as fixed effects. Carriers of the FecB
had a higher dressing percentage (+1·15%), longissimus muscle depth (+0·26 mm to +0·7 5mm) and cross-sectional area (+0·98 cm2). However the gene also had a positive effect on subcutaneous fatness (+0·12 points), KKCF (+30 g) and a substantial positive lamb carrier effect on carcass fat tissue content (+3·09%), which reflects a relative increase in fatness of 11·9%. The FecB
gene had also very small, significant effects on some meat colour traits. The dam carrier effects of the Booroola gene were negatively associated with food efficiency and with longissimus muscle depth (–1·38 to –2·25 mm). The increased fatness of lambs could imply that for optimal use of FecB
, non-carrier terminal sires should be used on heterozygous dams.