The course of pregnancy was followed in three groups of Peppin-strain Merino ewes. Group 1 of seven ewes, maintained on a high plane of nutrition, all lambed; the mean birth weight of lambs was 8 lb. 6 oz. The six ewes in group 2, kept on a low plane of nutrition, all lambed; the mean birth weight of their lambs was 1 lb. 9 oz. lower (P<0·01). The seven ewes in group 3 kept on a low plane of nutrition and subjected daily to temperatures of 112° F. dry bulb, 92° F. wet bulb, produced only four lambs; the mean birth weight was 4 lb. 6 oz. less than those from group 1, and 2 lb. 13 oz. less than those from group 2 (P < 0·001).
Scale photographs of the lambs, and X-rays and measurements of their long bones, after dissection, showed that the lambs of group 3 were miniatures: their skeletons were much reduced in size, whereas low nutrition alone (group 2), caused little skeletal reduction.
The mechanism of dwarfing is not clear. However, fore-cannon bone lengths and liver weights, considered in relation to lamb birth weights indicated that it was not a nutritional effect.
This study was undertaken at the Physiology Department, University of Queensland. It is a pleasure to thank Prof. W. V. Macfarlane for the valuable facilities, and for his help and encouragement.