Faba bean (Vicia faba) inclusion in dairy cow diets: Effect on nutrient digestion, rumen fermentation, nitrogen...

The objective of this study was to determine the effect of replacing on isonitrogenous and isoenergetic basis soybean meal (SBM) and corn grain with ground or rolled faba bean (FB; Vicia faba major var. Baie-Saint-Paul) in dairy cow diets (17% of diet dry matter) on nutrient digestion, rumen fermentation, N utilization, methane production, and milk performance. For this purpose, 9 lactating cows were used in a replicated 3 × 3 Latin square design (35-d period) and fed (ad libitum) a total mixed ration (forage:concentrate ratio = 59:41 on a dry matter basis). In the concentrate portion, SBM and corn grain (control diet) were completely and partially replaced, respectively, with either ground or rolled FB. Ruminal degradability (in sacco) of crude protein was higher for ground FB (79.4%) compared with SBM (53.3%) and rolled FB (53.2%). Including FB in the diet did not affect dry matter intake, milk production, and milk composition. Experimental treatment had no effect on total volatile fatty acid concentration, acetate-to-propionate ratio, and protozoa numbers. Compared with cows fed the control diet, ruminal NH₃ concentration increased and tended to increase for cows fed ground FB and rolled FB, respectively; however, we found no difference in ruminal NH₃ concentration between the 2 processed FB. Apparent total-tract digestibility of crude protein was similar between cows fed the control diet and cows fed rolled FB and tended to increase for cows fed ground FB compared with cows fed the control diet. Feeding rolled FB decreased CP digestibility compared with feeding ground FB. Urinary and manure (feces + urine) N excretion (g/d or as a proportion of N intake) were not affected by the inclusion of FB in the diet. Enteric CH₄ production was similar among the experimental diets. Results from this study show that including FB (17% of dietary dry matter) at the expense of SBM and corn grain in the diet had no effect on milk production, N excretion, and enteric CH₄ production of dairy cows.