The efficiency of microbial protein production from tropical forages and its measurement using spot samples of urine and CrEDTA clearance from the plasma

Abstract

The efficiency of microbial crude protein production (MCP) expressed as g MCP/kg digestible organic matter (DOM) was much lower (P <0.05) in cattle consuming pangola grass hay (P, a tropical grass) than rye grass hay (R, a temperate grass) (87 vs 191 g MCP/kg DOM respectively). This agreed with a collation of experimental data from the authors' laboratory indicating that tropical forages always had lower values than the values in international feeding standards. The excretion of creatinine was too variable for it to be used as an internal marker in spot samples (0.76-1.45 mmole/W0.75/d). The fractional disappearance rate of CrEDTA from the plasma was similar for cattle consuming either hay (1.26-1.54%/min). The glomerular filtration rate (GFR) estimated from urinary creatinine excretion was significantly different (289 L/d vs 793 L/d, P vs R respectively). The ratio of predicted allantoin clearance determined by reference to plasma volume and FDR of CrEDTA to the actual urinary excretion was 6.7 and 9.6 for R and P respectively. This difference meant that clearance of CrEDTA could not be used as a technique in association with plasma concentration of allantoin to estimate urinary excretion of allantoin.