Evaluation of NRC Method of Estimating Body Protein to Lipid Ratio in Growing Pigs

A study was conducted to evaluate the accuracy of the equation estimating body lipid to body protein ratio (BLBP) of growing pigs proposed in the NRC (2012) model. In this model, BLBP is set as initial condition for growing finishing pigs to predict body composition from BW and is described by the equation: BLBP = (0.305 – 0.000875 * PD_Max) * BW^0.45; where PD_Max (g/d) is the maximum protein deposition potential of the animal. The assessment was done using body composition data of 57 growing barrows (28±2 kg BW) of a terminal cross line. The body protein and lipid content was measured using dual energy absorptiometry (DXA). The mean protein deposition of barrows from 25 to 55kg BW (n=19) and 70 to 100 kg BW (n=20) from the same batch was used to extrapolate the representative PD curve of the barrows as described in NRC (2012). The maximum value from the curve was used as PD_Max (190 g) in the BLBP equation. All the animals were fed at or above recommended nutrient requirements. The residual error analysis for BLBP prediction by NRC equation revealed a root mean squared prediction errors (RMSPE; as a percentage of observed mean) of 35%. The average BLBP predicted value was 0.62 while the average observed value was 0.94. Most of the errors (89%) were due to mean bias and some were due to slope bias (9%). These errors indicate that the NRC proposed BLBP equation under estimate BLBP. When the default PD_Max (145 g/d) for growing barrows was used for BLBP prediction, the RMSPE was reduced to 19% with 60% of errors partitioned to mean bias and 33% to slope bias. It was thus concluded that the BLBP equation used in the NRC 2012 model underestimates body lipid to body protein ratio in pigs with high genetic potential for protein deposition.