| Abstract: | A comparison has been made of the three isotopes, deuterium, tritium and 42K for the measurement of body composition of wether sheep by the dilution technique. Eighteen sheep of a small breed were divided into three groups of six and given either a high, maintenance or low plane of nutrition. After an interval of 6-9 weeks the sheep were injected with the three isotopes, slaughtered within 24 h and composition determined directly by chemical analyses. The live weight at the time of slaughter ranged from 21.6 to 34.8 kg and the fat content from 9.9 to 19.7% of live weight. Tritiated water under-estimated total body water by 4.6 ± 3.1 g per 100 g. The overall mean for deuterium oxide agreed closely with that for total body water but the actual results were a little more variable than those for tritiated water. Mean exchangeability of potassium for all wethers was 89.4% and a very close relationship was found between exchangeable potassium and total body potassium. For the prediction of empty body nitrogen, the inclusion of either tritiated water space, deuterium oxide space or exchangeable potasium along with live weight in a multiple regression improved the precision over the use of live weight alone. Similarly multiple regressions including either deuterium or tritium space with live weight predicted body fat content with significantly greater precision than live weight alone and tritiated water was significantly better than deuterium oxide for this purpose. Either tritiated water space or exchangeable potassium with live weight significantly improved the prediction of fat-free empty body weight over the use of live weight alone, and tritiated water was significantly better than 42K for this predictive purpose. |
