A Study of Some of the Conditions Affecting the Rate of Excretion and Stability of Creatinine in Sheep Urine

Abstract

Some of the factors affecting the stability and rate of excretion of urinary creatinine of sheep were studied with special reference to those conditions expected to have practical significance in investigations in which creatinine is used in the prediction of body composition in ruminants. Creatinine was found to be unstable and to decay rapidly at the normal pH (8.4 to 8.7) of sheep urine under temperatures ranging from 15 to 39°C. However, no loss of creatinine occurred during a 5-month period when urine was stored at its normal pH but at 4°C. The storage of urine acidified to a pH of 2.5 to 3.5 and held at a temperature of 28 or 39°C resulted in a progressive increase in creatinine concentration with increasing time of storage. The average rates of recovery from urine of creatinine administered orally, via abomasal fistula and by intravenous injection were 3.5, 14.3, and 83.3%, respectively. In contrast to nonruminants for which urinary recovery of orally administered creatinine is as high as 80%, the sheep was not found to absorb exogenous dietary creatinine to any appreciable degree. Microbial utilization or destruction of creatinine in the stomach compartments of the sheep is thus only partly responsible for the poor absorption of creatinine. Since 16.7% of the intravenously administered creatinine was not recovered in the urine, it is indicated that a significant fraction of creatinine may be voided from the body via such routes as the sweat, saliva and the digestive tract. Abrupt, large increases in the protein intake resulted in increased outputs of urinary creatinine. Starvation resulted in a reduction in urinary creatinine. The carry-over of these effects following the return of the animals to the control diet was sufficient to indicate that the changes in creatinine output were at least partly attributable to concomitant changes in body composition.