1. Diethylstilboestrol administered orally to a Shorthorn cow had no marked effect on milk yield or composition.
2. A series of injections of the dipropionate in oily solution led to a slight rise in non-fatty solids in the same cow as in 1. Single larger injections were followed by a rise in milk solids accompanied by a rapid fall in milk yield in two other Shorthorns.
3. Inunction with an ointment containing the dipropionate led to a marked increase in milk solids in a Shorthorn cow, with no change in milk yield. The effect subsided rapidly when treatment was stopped. No significant effects were produced by similar treatment of four pregnant British Friesians; on increasing the dose two of these aborted. A Guernsey cow showed a slight increase in nonfatty solids and a slight but temporary fall in milk yield.
4. Subcutaneous implantation of crystalline diethylstilboestrol led to a striking and prolonged increase in milk solids, with no fall in milk yield, in a Shorthorn cow.
5. Subcutaneous injection of an aqueous suspension of diethylstilboestrol (1 g.) was equally successful when applied to the same cow as 4, but in the next lactation. In three Ayrshires the increase in solids was accompanied by an appreciable decline in milk yield. A Shorthorn receiving 375 mg. showed a temporary rise in solids, while one receiving 225 mg. showed no effect.
6. In all cases where milk yields declined the milk solids percentage rose, but the converse did not hold. Hence the threshold dose for inhibition is apparently higher than for enrichment.
7. The threshold doses may depend on the breed; the most successful results were obtained with Shorthorns.
8. Treated cows may be difficult to get in calf subsequently, especially those treated twice.
9. Administration of large doses of diethylstilboestrol to cows in advanced pregnancy results in abortion.
10. The enrichment of the milk in favourable cases represented a true increase in the yield of solids secreted, and not merely a concentration due to reduced secretion of water.