Evaluation of urinary creatinine excretion to estimate in vivo body composition of Belgian Blue double-muscled bulls

Urinary creatinine excretion (UCE) and chemical body composition of 18 Belgian Blue double-muscled bulls were determined. Paltry due to the large fasted live weight (fLW) range (308-710 kg), kg water and protein in the empty body were quite accurately predicted (adjR(2) = 0.94 and 0.97) by UCE. The precision of the prediction of kg empty body fat was less good (adjR(2) = 0.77). However, the empty body composition of the bulls varied only slightly and linearly with increasing live weight so that the fLW was the beat parameter to estimate empty body water and protein with an adjR(2) Value of 0.99 for both. The empty body fat was estimated from fLW with an adjR(2) = 0.75. The equations predicting relative body composition from UCE had much smaller adjR2 values, varying from 0.53 for % empty body water to 0.30 for % empty body protein. However, the coefficients of variation were much smaller. The prediction of the relative composition based on UCE was always somewhat better than based on fLW, but the improvement was not enough to justify the work involved in determining UCE. Conclusively, due to the small compositional changes, UCE did not significantly improve the estimation of the body composition from fLW. From the comparison of the results with other studies, it can be concluded that the double-muscled bulls have an extremely high urinary creatinine concentration, which cannot entirely be explained by their increased protein content.