Relationships between deuterium dilution space and estimated energy balance in lactating goats

In this study the effects of pregnancy, diet and stage of lactation on energy balance of dairy goats were compared. Energy balance was predicted both with the deuterium oxide technique and with measurement of energy consumption and the requirement for milk production, pregnancy and maintenance. The study was a 2 X 2 Latin square design with two different diets (15.6% and 25.9% ADF in DM) fed in two periods to two groups of three lactating does housed in digestion crates. Each period lasted 4 weeks and was preceded by an adaptation period of 2 weeks. A complete energy balance was calculated for each goat in each period by measuring daily feed intake, milk yield, faeces and urine. Energy retention was calculated as difference between the total milk net energy intake and the milk net energy used for maintenance, pregnancy and milk production. Changes in body composition between the beginning and the end of each period were estimated by means of the deuterium technique, and energy retention was calculated using 39.6 MJ and 23.6 MJ kg(-1) caloric equivalent for fat and protein gains, respectively. Data were analysed according to a split-plot model in which pregnancy, diet and period were fixed effects and animal nested in pregnancy was a random effect. The two approaches provided similar estimates of the average effects of pregnancy, diet and period on energy retention. Higher variability was observed with the isotopic procedure. The precision and accuracy of the isotopic procedure can be improved by increasing the number of experimental animals and the length of the trial.