A simple laboratory method for estimating the standardised precaecal digestible crude protein in pig feeds

Summary

Adequate protein supply for pigs to sustain performance and animal health can be determined in vivo from standardised precaecal digestible (pcd) crude protein (pcdCP). Until now, only time-consuming methods are available to estimate pcdCP from laboratory measurements without in vivo experiments. Therefore, the objective was to develop and establish a rapid laboratory method for estimating pcdCP based on the determination of neutral-detergent-insoluble or acid-detergent-insoluble crude protein (NDICP, ADICP). The CP was determined for cereal grains on the neutral detergent residue and for all protein feeds on the acid detergent residue, because N compounds such as Maillard products or N bound to tannin or in phytate complexes are retained in the acid detergent-insoluble fraction. A unique, large sample pool of 82 feed ingredients (cereal grains, differently heat-treated legume grains) was available on which in vivo pcdCP were determined in cannulated pigs. Crude protein (N ∙ 6.25) was determined in feed ingredients and in their ND or AD residues. The concentrations of ND- and AD-soluble CP (NDSCP, ADSCP) were calculated by difference. For the estimation of the concentrations of in vivo pcdCP for the entire dataset, a linear relationship was established between the concentrations of NDSCP or ADSCP and the in vivo pcdCP: y = 0.8640 (standard error [SE] 0.019) x - 13.37 (SE 7.479), where y represents the in vivo pcdCP (g/kg dry matter) and x represents the NDSCP (cereal grains) or ADSCP (protein feeds) value (g/kg dry matter). The coefficient of determination (R2) of this equation was 0.962. A validation with literature values showed a good fit of the equation to an independent data set (n = 20; R2 = 0.955). This study shows that based on chemical analysis alone, namely determination of NDICP and ADICP, from which NDSCP and ADSCP are calculated, in vivo pcdCP values can be estimated with a standardised and rapid laboratory method.