Factors affecting urinary creatinine in heifers and cows.

A series of total urine collections were conducted to evaluate the effects of age, diet, gestation, and body condition score ( BCS ) on urinary creatinine ( UC ) and purine derivative ( PD ) excretion in heifers and cows. For each collection, urine was collected over a 5-d period and composited by animal within day. Daily samples were analyzed for UC and PD concentration and averaged over the 5-d period. All animals were fed in individual stanchions at 2.0% of body weight ( BW ). To evaluate the relationship between age and UC excretion, 21 animals ranging from 5 to 80 months of age were fed a forage-based diet supplemented with dried distillers grains (DDG). Creatinine excretion (mg/kg BW) was not correlated with age ( P = 0.37). To determine if diet alters UC, 11 heifers were sampled for two urine collection periods. In period 1, heifers were fed a forage-based diet supplemented with DDG. In period 2, heifers were fed a finishing diet (90% concentrate, 10% forage). Creatinine excretion (mg/kg BW) and PD:creatinine ( PD:C ) was greater ( P = 0.01) for heifers when fed the forage-based diet than when fed the concentrate-based diet. Eleven cows fed a forage-based diet supplemented with DDG were sampled to determine the effect of gestation on urinary metabolites. Gestation did not affect UC ( P = 0.42) or PD:C ( P = 0.30). To evaluate the relationship between 12th rib fat thickness and metabolite excretion, 40 heifers were fed a common finishing diet. There was no relationship between UC (mg/kg BW; P = 0.28) or PD:UC ( P = 0.47) and 12th rib fat thickness. To evaluate the relationship between BCS and UC, 11 cows were fed a forage diet supplemented with DDG. There was no relationship between BCS and UC (mg/kg BW; P = 0.99) or PD:C ( P = 0.84). To evaluate daily and diurnal variation in UC, nine heifers were fed a forage diet supplemented with DDG. Seven of the heifers were fed a finishing diet (90% concentrate, 10% forage) in a second period. Urine was collected every 2 h from 0600 to 1800 hours. When expressed as mg/kg BW, UC excretion was not different across animals fed the forage-based ( P = 0.40) or concentrate-based diet ( P = 0.18). Stepwise regression indicated that at least 3 d of collection were required to estimate UC. Time within day and day within period effects were observed ( P < 0.01) for UC from 2-h interval samples. The UC varies with type of diet and diurnal variation is present. Variation among animals is relatively small.
(© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science.)