Prediction of in vivo apparent total tract energy digestibility of barley in grower pigs using an in vitro digestibility technique

The DE content within cereal grains can vary 25% mainly due to changes in apparent total tract digestibility (ATTD) of energy. In vitro digestibility techniques have been developed to predict the DE value among feedstuffs. However, these techniques have not been tested properly for their suitability to predict the variation in energy digestibility and DE content within a cereal grain. The objective of the present study was to establish and evaluate an in vitro digestibility technique to predict in vivo ATTD of energy of barley in grower pigs. Barley grain samples (hulled, n = 21) with a large range in quality were collected; the ADF and CP content ranged from 4.5 to 11.4% and 10.0 to 16.4% (DM basis), respectively. The ATTD of energy was determined using barrows (n = 63, 33 ± 2.1 kg of initial BW) in 2 periods with 6 observations per sample and ranged from 51.9 to 78.5%, with relative errors between 0.4 and 5.0%. A preliminary study, comparing a 2- and a 3-step in vitro digestibility technique using 3 barley samples, indicated that R² between in vivo and in vitro energy digestibility was greater using the 3- than the 2-step technique (0.92 vs. 0.76). Therefore, the 3-step in vitro digestibility technique was used solely in subsequent analyses. Briefly, ground barley was subsequently incubated with pepsin for 6 h, pancreatin for 18 h, and cellulase for 24 h. The DM and GE content of samples and residues were measured to calculate digestibility. The in vitro energy digestibility of the 21 barley samples with duplicate measurements ranged from 63.7 to 82.2%, with relative errors between 0.1 and 2.6%. In vitro energy digestibility was strongly related (y = 1.25 x - 25.22; R² = 0.81) to in vivo energy digestibility. Finally, a subset of 7 barley samples was analyzed in quadruplicate using the 3-step in vitro technique. The relationship between in vitro and in vivo energy digestibility was very strong (y = 1.23 x - 25.33; R² = 0.97) with relative errors between 0.5 and 2.7%. In vitro DE and energy digestibility were perfectly related (R² = 1.00). In summary, the 3-step in vitro energy digestibility technique can accurately predict the ATTD of energy in barley in grower pigs. The 3-step in vitro digestibility technique, thus, might be useful as the reference laboratory procedure to calibrate analytical equipment to rapidly predict the ATTD of energy in barley.