(a) Genetic trends for litter size at birth (LSB), litter size at weaning (LSW) and lambing interval (LI). (b) Genetic trends for cumulative litter weight at birth (LWB), mean litter weight at birth/ lamb born (LMWB), cumulative litter weight at weaning (LWW) and mean litter weight at weaning/ lamb weaned (LMWW).