| Co-products are increasingly used as alternative feedstuffs for pigs, but their nutritional quality varies largely. Rapid evaluation of energy digestibility of co-products is important for the feed industry and pork production. In vitro digestion (IVD) models have been used to evaluate nutritional quality of feedstuffs, but not rigorously tested on co-products. In study 1, we examined the performance of an IVD model to predict the apparent total tract digestibility (ATTD) of energy of 30 co-product samples of canola meal, corn dried distillers grain with solubles (DDGS), soybean meal, and wheat millrun, and compared with the predictions based on chemical analyses. The IVD model explained 69% of the variation in ATTD of energy among the co-products, but the prediction error was large. Furthermore, the IVD model underestimated the ATTD of energy of corn DDGS and wheat millrun, and poorly described the variation of the ATTD of energy within co-products of canola meal, corn DDGS, and soybean meal. Currently, chemical analyses had greater accuracy than the IVD model to predict the ATTD of energy of co-products, but its prediction based on multiple chemical analyses is not favorable. To determine issues of IVD model for its further improvement, identification of discrepancies between IVD and in vivo digestion of nutrients is essential. In study 2, a novel approach of using functional group digestibility (FGD) was proposed to estimate crude protein (CP) digestibility. The apparent ileal digestibility (AID) of CP of wheat was accurately estimated (R2 = 0.99) using the FGD determined with the absorbance in the amide I region (1,689-1,631 cm-1) of Fourier transform infrared (FT-IR) spectra scanned with an attenuated total reflection (ATR) attachment and ratio of an inorganic indigestible marker in diet and digesta. In study 3, a spectroscopic method was proposed to evaluate fat digestibility. The AID of total fatty acids (R2 = 0.75) and ATTD of ether extract (R2 = 0.90) of flaxseed and field pea were estimated with the FGD at ca. 2,923 cm-1 and 1,766-1,695 cm-1 of ATR FT-IR spectra, respectively. Our findings can assist the further improvement of IVD model to evaluate energy digestibility of co-products. |
