Feeding novel low vicine and covicine, mid- or zero-tannin faba bean cultivars on energy, starch, protein and amino acid digestibility in growing pigs

Vicine and covicine content of faba bean cotyledons can induce favism, a haemolytic anaemia in humans with an erythrocyte deficiency of glucose-6-phosphate dehydrogenase. Tannins in faba bean hull (testa) offer frost tolerance during fall nights but may impair starch and crude protein (CP) digestibility. This study evaluated feeding novel low-vicine and covicine faba bean cultivars bred to reduce human health risk, with varying tannin levels on digestibility of energy, starch, CP, and amino acids (AA) in growing pigs. In a Youden square design, 13 ileal-cannulated barrows (32.6 ± 2.5 kg) were fed 1 of 9 faba bean cultivar diets (950 g/kg) and a nitrogen-free diet to correct for endogenous losses over 9˗11 periods consisting of 4 d of diet adaptation, 2 d of faecal collection, and 2 d of digesta collection. Low vicine and covicine, zero-tannin cultivars were CDC 219–16, DL 19.7202, DL Nevado, and Navi. Low vicine and covicine, tannin-containing cultivars were Allison, Dosis, Fabelle, and Victus. Cultivar starch and CP content averaged 381 and 276 g/kg (as is), respectively. Total and insoluble fibre were both 11 % greater in zero-tannin than mid-tannin cultivars. Amino acid content across cultivars averaged 18 g/kg Lys, 9 g/kg Thr, 5 g/kg Met + Cys, and 2 g/kg Trp. Cultivar vicine and covicine content was low (0.83 g/kg and 0.07 g/kg, respectively) except for CDC 219–16 (5.40 and 1.97 g/kg). Tannin content in mid-tannin cultivars was 83 % greater than in zero-tannin (13.3 vs. 7.3 g/kg). Coefficient of apparent total tract digestibility (CATTD) of dry matter (DM) and gross energy (GE) were 8 % and 10 % greater, respectively, in zero-tannin than mid-tannin diets (P < 0.01). Coefficient of apparent hindgut fermentation (CAHF) of DM and GE were 45 % and 77 % greater in zero-tannin than mid-tannin diets (P < 0.01). Zero-tannin cultivars had 5 % greater coefficient of standardised ileal digestibility (CSID) of CP and most AA than mid-tannin, except for Trp that was 9 % lower (P < 0.01). Zero-tannin vs. mid-tannin cultivars also provided 10 % greater digestible energy (DE) and predicted net energy (NE) values (13.36 vs. 12.13 MJ DE/kg; 8.62 vs. 7.77 MJ NE/kg, respectively; P < 0.01). In conclusion, despite greater fibre content, novel low-vicine and covicine zero-tannin cultivars had greater CATTD and CAHF of DM and GE, greater CSID of CP and AA, and greater DE and NE values than the mid-tannin cultivars.