Determination of the energy content and amino acid digestibility of double-low rapeseed cakes fed to growing pigs

• The SID and AID of CP and AA of double-low rapeseed cake (DLRSC) were determined.
• The DE and ME values of DLRSC for growing pigs were measured.
• The DE and ME values of DLRSC varied with their ether extract and fiber content.
• Increasing fiber content will decrease the AA digestibility of DLRSC.
• Increasing lysine content will increase the AA digestibility of DLRSC.

Two experiments were conducted to determine the digestible (DE) and metabolizable energy (ME) content as well as the apparent (AID) and standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in double-low rapeseed cakes (DLRSC) fed to growing pigs. In Exp. 1, 66 growing pigs (initial body weight (BW): 36.6 ± 4.1 kg) were randomly allotted to 1 of 11 diets (n = 6) including a corn-soybean meal basal diet and 10 DLRSC test diets. The basal diet was formulated using corn and soybean meal while the DLRSC test diets contained 192.2 g/kg DLRSC added at the expense of the corn, soybean meal and lysine. In Exp. 2, 9 growing barrows (initial BW: 29.7 ± 3.1 kg) were surgically fitted with a T-cannula in the distal ileum and allotted to a 6 × 9 Youden square design with 6 periods and 9 diets. The diets included a N-free diet containing 689 g/kg cornstarch and 200 g/kg sucrose and 8 test diets which were formulated to include 400 g/kg of one of the DLRSC samples. The chemical composition of the 10 DLRSC samples varied considerably especially for aNDF, ADF, calcium, phosphorus and total glucosinolates. The DLRSC samples had a similar AA composition (CV < 10%) with the exception of lysine (CV = 23.5%). The DE and ME content differed (P < 0.01) among the 10 DLRSC samples. On a dry matter basis, the DE (mean 14.51 MJ/kg) and ME content (mean 13.08 MJ/kg) varied from 12.64 to 15.77 MJ/kg and 11.93 to 14.41 MJ/kg, respectively. The apparent total tract digestibility coefficient of gross energy averaged 0.686 ranging from 0.596 to 0.728. The results of Exp. 2 showed the AID of CP and lysine averaged 0.65 and 0.68, respectively. For the indispensible AA in DLRSC, the SID of arginine (mean 0.883) and methionine (mean 0.897) were relatively high. In contrast, the SID of threonine (mean 0.706) and Lys (0.704) were relatively low. The SID of CP and lysine ranged from 0.652 to 0.806 and 0.554 to 0.862, respectively. In conclusion, there were great differences in the chemical composition, energy content and the SID and AID of CP and AA among DLRSC samples. These differences in chemical composition especially the ether extract, fiber and total glucosinolates content may be responsible for the variability often observed in the nutritional value of DLRSC.