The flock books of fourteen Lowland breeds of sheep were examined to study flock size, flock age, the number and source of rams used, the extent to which flocks differ in genetic importance within their breeds, the effect of geographical location on flock attributes, and changes in breed organization over a period of time.

All breeds taken together showed that 46% of the 2649 flocks involved had less than fifty breeding ewes and 15% had more than 200. 43% of flocks were less than 5 years old and 18% were over twenty. A third of all flocks used only one ram and 9% used five or more. All breeds were found to be arranged in a hierarchy such that only a small number of flocks in each breed supplied the majority of the rams and in particular the rams used by rambreeding flocks. The ‘top’ flocks were among the largest and oldest in each breed. Flocks in the ‘native’ region of each breed we e generally larger and older than those elsewhere, but for other flock attributes the differences between regions were more peculiar to breeds. The general pattern of breed organization appeared to apply at widely differing periods of time.