An experiment is reported in which copper, as cupric oxide, was fed to two breeds of laying hen for 336 d at levels equivalent to 150, 300, 450, 600 and 750 mg added Cu/kg diet. The results obtained were compared with those found using similar diets to which the Cu was added as CuSO4.5H2O. 2. Addition of the CuO had no effect on food intake, food conversion efficiency, body-weight or egg production. The CuSO4 addition caused the quadratic response of food intake and the adverse effects on food intake, egg production and body-weight noted in previous experiments. 3. The CuO had no effect on liver, kidney, ovary, oviduct or gizzard weight per unit body-weight while the CuSO4 decreased these with the exception of gizzard weight which was significantly increased. 4. CuO addition did not affect liver Cu concentration but CuSO4 caused a substantial increase of liver Cu especially at the 750 mg Cu/kg level of addition. 5. CuO addition had no effect on liver lipid concentration but this was depressed at the highest level of CuSO4 addition. Effects on individual fatty acids are presented but no specific conclusions have been reached.
