[Estimation in vivo of the body composition of the ewe by measuring the diffusion space of heavy water].

Relationships for estimating body lipids, energy and proteins from the deuterium-oxide (D2O) diffusion space have been determined using 38 dry, pregnant or lactating ewes. The animals were fed as usual and had free access to water up to slaughter. They were injected with deuterium-oxide in the morning, half an hour to 3 hours after being fed the whole daily ration or half of it. Blood samples were collected between 1 and 24 h after injection. The deuterium-oxide content of blood water was determined by infra-red spectrophotometry. The ewes were slaughtered 24 h after injection and their body water, protein, ash and energy were chemically determined. Different blood samples were used to measure the deuterium-oxide diffusion space (theoretical initial concentration Co method). The closest relationship between measured body water (ECM) and D2O diffusion space (ECD2O) was found when the blood sample collected 8 h after injection was discarded. Ewe body composition was estimated using a linear relationship in which ewe body weight and D2O diffusion space were two independent variable (relationship number 5). The best ewe body weight to use was the weight measured at injection time. The estimation of body lipid was significantly affected by physiological status when slaughter weight and true body water, measured at slaughter, were used. The effect of this physiological status decreased when the water content of the digestive tract was taken into account and it was no longer significant when the water content of the uterus and conceptus was considered. Body composition could always be predicted by estimating the water content; the standard error was nearly 1.4 kg. However, the method was not accurate enough to obtain a significant effect of physiological status on lipid estimation. Thus, at present we have proposed identical equations for dry, pregnant or lactating ewes.