Abstract Two hundred and fifty-six ewe lambs comprising 196 Suffolk × (Blue-faced Leicester × Swaledale) (SBS) and 60 Suffolk × (Cadzow Improver × Scottish Blackface) (SCS) were divided into three groups to be mated by Suffolk rams at either their puberal (O 1), second (O 2) or third (O 3) oestrus. One hundred and eighty-nine ewes were mated at the assigned oestrus. These were slaughtered either at return to oestrus or 25 ± 3 days post coitum. SBS ewes were heavier ( P < 0.05), although with a lower body condition score ( P < 0.01) than SCS ewes at mating. Spermatozoa were recovered from the vaginal mucus of 95% of all ewes mated, there being no differences between treatments. The percentage of ewes with living embryos increased from O 1 to O 2 ( P < 0.01) and O 3 ( P < 0.05), and was greater in SCS than SBS ewes ( P < 0.05); live weight and body condition score at mating, post-mating live-weight change and ovulation rate had no effect. A smaller percentage of O 1 ewes with a single CL had a living embryo than had O 2 or O 3 ewes ( P < 0.05). SBS ewes suffered greater losses than SCS ewes for those animals with 2CL ( P < 0.05). Neither oestrous period nor breed affected ovulation rate.