The use of deuterium oxide space to determine the amount of body fat in pregnant Blackface ewes.

I . The use of deuterium oxide dilution to obtain an indirect estimate of body water in pregnant ewes was examined and the value of such an estimate in predicting body fat was investigated. 2. Deuterium oxide was infused intravenously into fourteen twin-bearing Blackface ewes and blood samples were taken 6-7 h later. The animals were subsequently slaughtered. 3. Deuterium oxide concentration was estimated by infrared spectroscopy and the deuterium oxide space was calculated. Studies on dose rates and equilibration times were made with the Blackface ewes and some non-pregnant Dorset ewes. 4. The amount of body fat in each ewe was estimated from the deuterium oxide space using a prediction equation relating body fat to body water in twenty-five pregnant and non-pregnant ewes which had been slaughtered. 5 . Once satisfactory measurement of deuterium oxide concentration had been achieved, body fat predicted from deuterium oxide space differed from values obtained by analysis of the slaughtered animals by -0.8 to + 1.7 kg in seven ewes containing 52-21.4 kg fat. 6. The standard deviation from regression of percentage of body fat estimated from deuterium oxide space on percentage of body fat measured after slaughter was 1.2 percentage units. Thus deuterium oxide space was used to provide a useful measure of body fat in pregnant ewes.