Creatinine as a metabolic marker to estimate urinary volume in growing goats

The objectives of this study were to: (1) quantify the relationship between fasting body weight (FBW, kg) and urinary creatinine excretion (UCE, mg/d) in Boer goats; (2) evaluate the urinary volume estimates obtained from creatinine concentrations in the spot samples collected at different time points; (3) compare them with the 24-h observed urine volume. Thirty growing Boer goats (18 ± 2.2 kg initial BW) were distributed in a complete randomized design. Each collection period fell on 2 consecutive days and collector funnels were used. Spot samples were collected at 0, 4, and 8 h after morning feedings. These procedures were repeated in three runs 25 days apart to obtain different FBWs. All the samples were analyzed to quantify creatinine concentrations. The relationship between UCE and FBW was established by the following equations: UCE = 17.39 x FBW, r2 = 0.96, P < 0.01, RSD = 40.8; UCE = 23.50 x FBW0.9059, R2 = 0.96, P < 0.01, RSD = 40.9. The null hypothesis was accepted when predicted and observed values were compared (P > 0.05). Thus both linear and allometric relationships can be used to predict UCE. The spot samples obtained at 4 h after feeding could be used to estimate urinary volume (P < 0.05) instead of at 0 or 8 h. We conclude that UCE can be a metabolic marker to the estimate urinary volume of goats when calculated according to FBW with linear or allometric mathematical relationships.