Soyhulls as a replacement for forage fiber in diets for lactating dairy cows

Thirty Holstein cows in early and midlactation were fed one of five TMR for 12 wk in which soyhulls replaced 25 or 42% of the forage (alfalfa:corn silages, 1:1, wt/wt, dry basis). Within each amount of soyhull replacement, 33% of the silage was replaced with coarsely chopped alfalfa hay. All diets were isocaloric compared with the control diet, which contained 60% silage and no soyhulls. The high amounts of soyhulls fed with coarsely chopped hay improved DMI, and NDF intake and milk yield by 14, 33, and 9%, respectively, compared with the control diet. Addition of soyhulls at low or high amounts reduced milk fat yield and increased milk protein yield, but addition of hay to the high soyhull diet maintained milk fat yield similar to the control diet. The high soyhull diets increased DM digestibility by 7% compared with the control diet. Rumination time and acetate to propionate ratios were reduced by 43 and 24%, respectively, when high amounts of soyhulls were fed compared with the control diet. Soyhulls can successfully replace 42% of dietary forage when fed in combination with coarsely chopped hay in place of 33% of the dietary silage.