RESUMEN
Following intravenous infusion with approximately 300 mg deuterium oxide per kg body weight, blood was drawn from lactating Holsteins (Trial 1, n = 4, and Trial 2, n = 5) at suitable intervals for up to 12 days while the cows were maintained on dietary regimens to which they were well adapted. Time results for deuterium oxide concentration in blood were described best by the three-compartment open model system, which showed that the central, shallow peripheral, and deep peripheral body water compartments contained 27.1, 25.0, and 23.2% body weight in trial 1 and 33.7, 27.1, and 19.9% body weight in trial 2. Total body water estimates averaged 75.3 and 80.7% body weight during trials 1 and 2. Estimates for biological half-life of water were 4.6 and 3.2 days and those for water turnover were 68.9 and 109.7 liters/day, respectively. The data fitted the two-compartment open model system when observations made prior to 25 min post-administration were excluded from the analyses, because the central and shallow peripheral compartments were apparently lumped into one. Blood sampling at 0.5, 1, and 1.5 days following infusion and thereafter at 1-day intervals was adequate for the estimates of the one compartment open model system. Estimates of total body water, water biological half-life, and water turnover were similar for the different models. It is concluded that the three-compartment open model provides greater detail and insight into the water dynamics of lactating dairy cows having regular access to food and water, whereas the two- and one-compartment open model systems provide good approximations only.
Asunto(s)
Agua Corporal/metabolismo , Bovinos/metabolismo , Lactancia/metabolismo , Animales , Deuterio , Femenino , Cinética , EmbarazoRESUMEN
Body composition was studied in five animal groups (two 8-week-old calves, two 16-week-old calves, three Holsteins and three Jerseys in late lactation and two groups of cows each having a Holstein and a Jersey in early lactation). Each group was fed a different diet so as to effect wide variations in body composition. Body water volume and kinetics were estimated by deuterium oxide (D2O) dilution in trials lasting 10-12 days for each animal. The experimental animals were slaughtered at the end of the trials for direct chemical analyses of body components. The following prediction equations were derived from D2O measurements and direct chemical analyses (slaughter studies) in kilograms except energy, which is in megacalories: TBW = 1.501D0.898 (Sy.x = 0.285); P = 1.501 (D0.898 - 2.682T0.605); protein = 0.147P1.095 (Sy.x = 0.895); ash = 0.0381P1.057 (Sy.x = 0.298); fat = 0.00122P-2.769 LW4.275 (Sy.x = 0.342); energy = fat X 9.226 + protein X 5.926 where TBW = total body water, D = D2O space in kilograms, T = water turnover (L/day), P = predicted empty body water and LW = liveweight (kilograms). It was concluded that further studies are required, with more animals, to improve and/or verify the utility of the above equations.