ln vivo prediction of body composition from the dilution space of the deuterium oxide in two lactating Spanish dairy breed ewes

Thirteen Churra (5 forty days and 8 seventy,days after lambing) and twelve Latxa (6 forty days and 6 a hundred and twenty days after lambing) lactating dairy ewes were used to obtain predicting equations of body fat, protein and energy from the live weight and the dilution space of deuterium oxide (SD20). Ewes were injected with 0.6 gD 20/kgo f live weight in the jugular vein and blood samples were collec5te, d7, 29 and 31 hours after infusion. The D20 content of blood water was determined by infrared spectrometry, and SDZO was calculated as the ratio between the weight of the injected D20 and its predicted concentration at zero time. After the last bleeding ewes were sheared and slaughtered and the body water, fat, protein, ash and energy were chemically determined. The Churra ewes presented 2% more water and 1.7% less protein in the fat free empty body 40 days than 70 days after lambing and fat free empty body water content decreased linearly (R=-0.60) with empty body fat content. There was however a close negative relationship (R2=0.97) between the fat and water content of the fleece free body weight. Neither the breed nor the stage of lactation significantly affect this relationship. Body water was predicted from SD20 with a residual standard deviation (RSD) of approximately kg when a pool equation was considered, though for a same SD20, the Latxa ewes presented 1.76 kg more water than the Churra ewes. Body fat and energy were predicted from the live weight and measured body water with a RSD of 0.437 kg and 6.85 Mcal, respectively, when a pool equation was considered. The adjusted means of body energy differed significantly between breeds and when this effect was taken into account the RSD diminished to 3.10 Mcal. When SDZO was substituted for measured body water, the resulting RSD were 0.980 kg and 6.85 Mcal, respectively. The intercept of the prediction equation of body fat differed significantly between breeds and when this effect was taken in account the RSD decreased to 0.703 kg. The accuracy of the body protein prediction from the ewes sheared body weight (RSD=0.56k9g from the pool equation and 0.282 kg for equation taking into account the breed effect) was not improved by the inclusion of SD20 as a second predictive variable. The stage of lactation did not significantly affect any of the equations studied