Field records from Leicester, Texel, Oxforddown, Dorset, Shropshire and Marsh breeds from 1983 to 1989 were used to investigate the influence of environmental factors on weight at birth, 2 and 4 months and 0–60, 0–120 and 60–120 days gain. Significant effects of herd, year, litter size and sex were observed. Generally, lambs born in the middle of the lambing season were heaviest, and postnatal growth decreased with progressing lambing season. Lambs born by yearlings were smaller and had lower growth rates than lambs born by ewes of other age groups. Lambs born by 4–5 year old ewes showed the best performance. Two-way interactions between ewe age, litter size and sex were observed.