Evaluation of the nutritional value of faba beans with high and low tannin content for use as feed for ruminants

BACKGROUND: Faba bean varieties with low or zero tannin content have been developed in Canada to overcome the negative effects of condensed tannins on the utilization by ruminants of crude protein (CP) and starch. However, their nutritional value has not been evaluated for incorporation in dairy rations. The objectives of this study were to investigate (i) the chemical profile; (ii) the Cornell Net Carbohydrate and Protein System (CNCPS) protein and carbohydrate subfractions; (iii) the energy values; (iv) the ruminal, intestinal, and total digestibility of CP; (v) the metabolizable protein (MP) supply to dairy cows; and (vi) the protein‐inherent molecular spectral characteristics of brown‐seeded (var. Fatima) faba beans with high tannin content and yellow‐seeded (var. Snowbird) faba beans with low tannin content. RESULTS: The results revealed that Fatima beans had higher (P < 0.001) CP content than Snowbird (324 versus 295 g kg⁻¹ dry matter (DM)), and lower (P < 0.01) starch content than Snowbird (411 g kg⁻¹ DM versus 444 g kg⁻¹ DM). Fatima had a lower (P = 0.001) soluble subfraction (201 g kg⁻¹ DM versus 220 g kg⁻¹ DM) and higher (P < 0.05) slowly degradable fiber‐bounded (24.9 g kg⁻¹ DM versus 14.7 g kg⁻¹ DM) and non‐degradable (3.24 g kg⁻¹ DM versus 0 g kg⁻¹ DM) CNCPS CP subfractions than Snowbird. Fatima had higher (P = 0.03) MP content (117 g kg⁻¹ DM versus 111 g kg⁻¹ DM) and metabolizable energy content (ME) 3.12 Mcal kg⁻¹versus 3.10 Mcal kg⁻¹) than Snowbird. Molecular spectral intensities of amide I and II proteins (height and area) of Fatima were higher (P < 0.05) than those of Snowbird, reflecting their higher CP content. The ratio of protein spectral intensities, the amide I : amide II height ratio, and the α‐helix : β‐sheet height ratio differed (P < 0.05) between the two types of bean, highlighting differences in their inherent protein molecular structures. CONCLUSION: The (Fatima) faba beans with high condensed tannin content had higher MP and ME content. On average, both Faba beans had higher ME and MP content than barley grains, highlighting their promising nutritional value for dairy rations. © 2021 Society of Chemical Industry.