The introduction of refrigerated transport brought about many changes in the sheep industry. At this time, the Merino and its crosses were predominant, although most of the English breeds of sheep had been imported into New Zealand. In high rainfall areas, particularly in the North Island, the Merino proved to be unsatisfactory, mainly because of its susceptibility to foot troubles and to fleece rot and discolouration. Crosses with English breeds, notably the Lincoln, English Leicester, and Border Leicester, proved to be more successful and, after a number of generations of breeding, the Merino was almost completely ousted. From 1900 onwards the Lincoln gradually lost popularity in the North Island, largely because of difficulties in rearing the young stock. Its place was taken by the Romney Marsh breed, and today most of the North Island ewe flocks are of Romney breeding.

In the southern part of the South Island, the breed changes followed a pattern similar to that of the North Island. In the drier northern part of the South Island, crossing of the Merino with Lincoln and English Leicester rams seldom went beyond the first generation. The maintenance of these half-bred flocks was carried out in two ways: first, by the use of first-cross rams bred by mating Lincoln or Leicester rams to Merino ewes and, secondly, the breeding together of the half-bred sheep in successive generations. The latter method, combined with careful selection, gave rise to the Corriedale breed.

Although these changes in breed composition had started before 1882, they were hastened by the introduction of the lamb and mutton trade. From the viewpoint of meat production, ewes of the Halfbred, Corriedale, Lincoln, and Romney breeds were more satisfactory for breeding fat lambs than the pure-bred Merino ewe. The practice also arose of using sires of the specialised fat-lamb breeds for crossing with these ewes. In 1900 the popular breeds for this purpose were the Border Leicester, English Leicester, and Shropshire which together represented 28 per cent of the rams in use. The Southdown breed was of minor importance at this time but it increased rapidly in popularity and, in 1957, represented 24 per cent of the rams in use.

The main reason today for the widespread use of the Southdown ram for lamb production is the preference in the United Kingdom for light-weight carcasses with small joints and without excess fat. The Southdown, being a small, early maturing breed with good conformation, produces crossbred lambs which most nearly meet this requirement. Other breeds which are used to a limited extent are the Suffolk, South-Suffolk (a breed developed in New Zealand by interbreeding Southdown-Suffolk cross sheep), Border Leicester, Dorset Horn, Shropshire, and the recently re-introduced Dorset Down and Hampshire Down breeds. These breeds are larger than the Southdown and produce crossbred lambs which have a faster rate of growth, but are later maturing than Southdown cross lambs.