Concentration of metabolizable energy and digestibility of amino acids in Chinese produced dehulled double-low rapeseed expellers and non-dehulled double-low rapeseed co-products fed to growing-finishing pigs

Two experiments were conducted to determine and compare the digestible energy (DE), metabolizable energy (ME) and the coefficients of standardized ileal digestibility (CSID) of crude protein (CP) and amino acids (AA) in two sources of dehulled rapeseed expellers (RSE-DH1 and RSE-DH2), conventional rapeseed expellers (RSE-CV), cold-pressed rapeseed expellers (RSE-CP) and rapeseed meal (RSM) produced by Chinese double-low rapeseed fed to growing-finishing pigs. In experiment 1, 36 growing pigs [initial body weight (BW): 37.7 ± 4.8 kg] were randomly allotted to one of six diets (n = 6) including a corn-soybean meal basal diet and five rapeseed co-product test diets. The test diets contained 194.8 g/kg each of the five double-low rapeseed co-products added at the expense of corn and soybean meal in the basal diet. In experiment 2, six growing barrows (initial BW: 69.4 ± 4.4 kg) fitted with a T-cannula in the distal ileum were allotted to a 6 × 6 Latin square design with 6 periods and 6 diets. Diets included one N-free diet and five test diets which contained 400 g/kg RSE or RSM as the only source of CP and AA. On an as fed basis, dehulled RSE samples (RSE-DH1 and RSE-DH2) contained the lowest neutral detergent fiber and acid detergent fiber among rapeseed co-product samples. Dehulled RSE samples had greater lysine concentration than non-dehulled RSE and RSM. The coefficient of apparent total tract ileal digestibility (CATTD) of gross energy (GE) in RSE-DH1 (0.822) was greater (P < 0.05) than that in RSE-CV (0.700) and RSM (0.655), but the CATTD of GE did not differ among RSE-DH1, RSE-DH2 (0.782) and RSE-CP (0.722). On an as-fed basis, the ME value was greater (P < 0.05) in dehulled RSE (14.5 MJ/kg) than RSE-CV (12.2 MJ/kg) and RSM (10.4 MJ/kg). The RSE-DH1 (9.72 MJ/kg) and RSE-DH2 (9.33 MJ/kg) contained greater (P < 0.05) calculated net energy value than RSE-CP (8.03 MJ/kg), RSE-CV (7.84 MJ/kg) and RSM (5.66 MJ/kg). With the exception of phenylalanine and valine, the CSID of CP and all AA in dehulled RSE was greater (P < 0.05) than that in RSE-CV and RSM. The CSID of CP and most of AA in RSE-DH1 was greater (P < 0.05) than that in RSE-CP. In conclusion, compared with non-dehulled rapeseed co-products, dehulled double-low rapeseed expellers may be a better energy and protein source for pigs considering its greater ME value and CSID of AA.