Replacement of forage or concentrate with combinations of soyhulls, sodium bicarbonate, or fat for lactating dairy cows.

A lactation study was performed from wk 4 to 19 of lactation to evaluate the ability of soyhulls with or without 1% sodium bicarbonate to replace corn silage and the ability of soyhulls, roasted soybeans, and rumen-inert fat to replace concentrate. All diets contained similar concentrations of NE(L) (tabular value), CP, and degradable protein. When forage NDF was reduced to 62.5% of total dietary NDF (32 to 36% NDF, depending on analytical method) with soyhulls, milk production and total tract nutrient digestibility were unaffected. Addition of sodium bicarbonate to the soyhull diet reduced milk production, but other production aspects were similar. As evaluated using body condition scoring, cows fed soyhulls with buffer appeared to lose less condition before the trial and to recondition earlier and more during the trial than did those fed soyhulls without buffer, which explains differences in milk production. Buffer did not increase digestibility of OM and NDF, perhaps because the high rate of passage of soyhulls limited digestibility more than did ruminal pH. Replacement of concentrate with soyhulls and fat tended to increase milk and FCM production, resulting in improved efficiency of milk production. However, fat fed to cows reduced the percentage of milk protein. As evaluated during the last 4 wk of a 6-wk posttreatment period, fat fed to cows had no residual effects on any production aspect measured.