Creatinine and pseudouridine in plasma and urine from Brahman-cross steers fed a low, medium or high plane of nutrition

Metabolic state as influenced by growth rate may influence meat toughness and can be estimated from metabolites excreted in urine. Urine collection over 24 h requires animals to be constrained in metabolism crates for many days. Single blood sampling to estimate metabolites in plasma would be less stressful on animals than collecting 24 h urine excretion. This study investigated the hypothesis that the plasma concentrations of pseudouridine and creatinine were representative of those found in 24 h urine excretions in steers fed different quality diets. Eleven Brahman-cross steers were fed a high (n = 3), medium (n = 4) or low (n = 4) quality hay diet for three weeks. Steers were catheterized and housed in metabolism crates for 6 days. Urine was collected every 24 h and total volume sub-sampled for analyses of creatinine and pseudouridine. Jugular blood was collected from each steer every 3 h from 07:30 to 16:30 h. Plasma was separated from red blood cells by centrifugation and frozen for creatinine and pseudouridine analyses. No time of day effect was apparent for pseudouridine or creatinine so daily means were used to test for effect of diet and to relate to urinary concentrations. Nutritional restriction halted live weight gain but had no effect on urinary or plasma pseudouridine, suggesting that diet did not affect tRNA turnover. Increased plasma creatinine concentrations and reduced urinary creatinine concentration in steers experiencing nutritional restriction indicated that their renal clearance rate decreased. As a result, the ratio of plasma pseudouridine to creatinine concentration was not directly proportional to that of 24 h urinary excretion.