In vitro digestibility techniques to predict apparent total tract energy digestibility of wheat in grower pigs1,2

In vitro digestibility techniques have been developed to predict the apparent total tract digestibility (ATTD) of energy and DE content of mixed diets and feedstuffs including barley grain in swine. However, the techniques have not been tested properly for their accuracy in predicting the variation in ATTD of energy and DE content within wheat grain. The objectives were 1) to compare two 3-step in vitro digestibility techniques with either cellulase (IVD-CEL) or Viscozyme (a multienzyme complex to digest fiber; Novozymes, Bagsvaerd, Denmark; IVD-VIS) as the third step, and differing in the amount of enzymes used and the duration of digestion, for their accuracy in predicting ATTD of energy and DM of wheat in grower pigs; and 2) to develop equations to predict ATTD of energy of different batches of wheat. Wheat grain samples (n = 20) with a wide range in quality were collected; the ADF and CP content ranged from 3.3 to 6.2% and from 11.2 to 20.8% (DM basis), respectively. The ATTD of energy was determined using barrows (n = 60, 30.7 ± 4.7 kg of initial BW) in 2 periods with 6 observations per sample, and ranged from 73.3 to 84.5%. In IVD-CEL, 1 g of ground wheat was digested sequentially in digestion solutions containing pepsin (10 mg/36.5 mL) for 6 h, pancreatin (150 mg/54.5 mL) for 18 h, and cellulase (75 mg/55.5 mL) for 24 h. In IVD-VIS, 0.5 g of ground wheat sample was digested sequentially in solutions containing pepsin (25 mg/36.5 mL) for 2 h, 3 mL of pancreatin (100 mg/54.5 mL) for 6 h, and Viscozyme (0.5 mL/65.3 mL) for 18 h. The in vitro energy and DM digestibility ranged from 79.8 to 91.0% and from 82.0 to 91.5% for IVD-CEL, and ranged from 76.2 to 87.0% and from 79.1 to 89.4% for IVD-VIS, respectively. The Rsup2 between ATTD of energy and in vitro DM and energy digestibility for IVD-VIS (0.82 and 0.73, respectively) was greater than for IVD-CEL (0.55 and 0.54, respectively). The equation y = 1.05x - 8.85 using the in vitro DM digestibility value from IVD-VIS can predict the ATTD of the energy of wheat in swine with an SE of prediction of 1.2. The relationship between in vitro DM digestibility and grain characteristics such as ADF was stronger for the IVD-VIS than for the IVD-CEL technique (Rsup2 = 0.89 vs. 0.70). In conclusion, the IVD-VIS, but not the IVD-CEL, technique can accurately (Rsup2 = 0.82) predict the ATTD of energy in wheat in grower pigs. Therefore, the IVD-VIS technique might be useful as the reference analysis to calibrate analytic