Factors which affect the growth of the lamb are of considerable economic importance in animal production. Most workers in this field have shown that growth rates are influenced to a large extent by milk production, especially in the early stages, hence the study of the yields, composition and persistency of lactation is of the utmost importance. Information was sought in this trial on the lactation performances of the Merino, Corriedale and Romney ewes grazing under high country conditions. This trial was designed to measure the relative milk yields and milk composition between the three breeds run in this environment. In general it is hoped that this trial will increase the knowledge on some of the factors influencing growth rates both quantitatively and qualitatively in this somewhat different environment.