Wet Corn Gluten Feed Fed Fresh or Stored and Supplemented with Rumen Undegradable Protein in the Diets of Lactating Dairy Cows

The main objective was to evaluate replacing fresh with long-term stored wet corn gluten feed (WCGF) in lactating cow diets and to evaluate added levels of rumen undegradable protein (RUP) to diets with WCGF. Twenty-four multiparous Holstein cows averaging 558 ± 45 kg of BW and 57 ± 35 d in lactation were stratified by age, days in milk, and milk yield and assigned to one of four treatments: 1) fresh WCGF, 5.4% RUP DM; 2) stored WCGF, 5.4% RUP DM; 3) stored WCGF, 6.3% RUP DM, and 4) stored WCGF, 7.2% RUP DM. Total mixed rations containing 19% dietary DM as WCGF were formulated to be isonitrogenous (17.2% CP) and isoenergetic (7.20 MJ NEl/kg of DM). The substitution of fresh WCGF as stored WCGF did not affect (P>0.10) milk yield or composition. Supplementing stored WCGF with RUP did not alter (P>0.10) actual or adjusted milk yield, but milk casein (P=0.03), fat (P=0.04), and total solids (P=0.03) increased in a linear fashion with increasing RUP supplementation. Ruminal ammonia concentration increased linearly (P<0.05), and total ruminal volatile fatty acid concentrations were similar among treatments; acetate increased (P<0.05), and butyrate decreased (P<0.05) with increasing levels of supplemental RUP. The WCGF may be stored for extended periods in an oxygen-limiting environment without reducing palatability or nutrient availability. Adding RUP may increase milk components when used in diets balanced for the nutrient demands of high producing dairy cows.