About 350 single- and 250 twin-born female Ayrshire cattle were compared on the same feeding regime in respect of 12 linear body measurements at 3-monthly intervals up to 36 mo of age, and some two-thirds of them up to 48 mo. The twins were purchased from a wide variety of farms, and it is unlikely that their dams were significantly better fed, in pregnancy, than the dams of single calves.

The effects of month and year of birth and age at first calving (including some pregnancy and lactation effects) were estimated by least-squares procedures. The trends of the differences between single and twin-born animals were analysed as percentages of current and of mature size. Earliness of maturing had no apparent effect. For the traits of height and girth, twin-born animals were smaller than single-born by nearly 2 % of mature size (3 % of current size) at 3 mo of age and for the other traits the difference was around 1 %. By 12 mo the differences were generally about half their initial value and remained at this level, except for head width where the difference declined to zero around 2 years of age.

It is concluded that twin-, compared to single-born, cattle are subject to a small degree of permanent stunting in most linear measurements.