Nitrogen utilization, nutrient digestibility, and excretion of purine derivatives in dairy cattle consuming rations containing corn milling co-products.

The objectives of this experiment were to determine the effects of feeding a combination of modified wet distillers grains with solubles (WDGS) and wet corn gluten feed (WCGF) on nutrient digestion, purine derivative excretion, and N utilization. Multiparous (n=20) and primiparous (n=20) cows were arranged in a replicated 5 x 5 Latin square with 21-d periods. Animals were fed one of 5 treatment diets during each period: 1) 0% co-products (control); 2) 15% WDGS (15WDGS); 3) 15% WCGF (15WCGF); 4) 7.5% WDGS and 7.5% WCGF (15MIX); and 5) 15% WDGS and 15% WCGF (30MIX; dry matter basis). A portion of forages, corn, and soy-based protein was replaced with WDGS, or WCGF, or both. Dry matter intake was greater for 15WDGS (25.1 kg/d) and 30MIX (25.5 kg/d) than for control (22.4 kg/d), 15WCGF (23.2 kg/d), or 15MIX (23.5 kg/d). Dry matter digestibility was greatest for 15WCGF and 30MIX (63.6 and 64.1%, respectively) and least for 15WDGS (59.8%), and neutral detergent fiber and N digestibility were greatest for 30MIX (50.7 and 68.6%, respectively) and lowest for 15WDGS (41.3 and 61.5%, respectively). Excretion of purine derivatives in urine was greater for co-product treatment diets than for control. Fecal N was greatest for 15WDGS compared with other treatment diets (311.0 vs. 263.3 g/d), whereas urinary N was greatest for 30MIX (330.0 g/d), intermediate for 15WCGF and 15MIX (319.3 and 320.5 g/d, respectively), and lowest for control and 15WDGS (308.5 and 312.2 g/d, respectively). Manure N (fecal+urinary N) was greatest for 15WDGS, intermediate for 15MIX and 30MIX, and lowest for control and 15WCGF. Treatment diets did not differ in 4% fat-corrected milk production. Compared with the ration containing WDGS, the ration with a 30% mixture of WDGS and WCGF improved nutrient digestibility and N utilization with reduced manure N excretion and increased N retention. Thus, it appears feeding WDGS and WCGF in combination reduces some of the negative effects of feeding WDGS alone. Copyright (c) 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.