Results of two-way selection for multiple births are reported, in a flock of Australian Merinos.Base ewes, selected for having multiple or single births at each of two lambings at 5 and 6 years of age have shown a good repeatability, the T group (multiple-bearers) having averaged 31 more lambs per 100 ewes mated than the O group (single-bearers) for 6 subsequent lambings.Unselected daughters of the base ewes, now ranging in age from 2 to 6 years, have also shown a difference in lamb drop, those in the T group averaging 21 more per 100 ewes mated. The difference in lamb drop has increased with the age of the daughter ewes, reaching 31 lambs per 100 ewes mated at 6 years of age.A small group of Merino ewes from a property where selection for multiple births is practised has produced 1·60 lambs per ewe mated at 2 and 3 years of age.It is suggested that earlier low estimates of heritability for the incidence of multiple births have led to unwarranted pessimism, and that in some circumstances selection for multiple births may be successful.

Merino sheep from two groups selected for single and multiple births were examined by laparotomy. Comparison of observed corpora lutea with previous lambing records suggests that differences in fecundity obtained by selection are due to genetic differences in number of eggs shed.