Short communication: Nutrient utilization of fresh sugarcane-based diets with slow-release nonprotein nitrogen addition for control-fed dairy heifers.

An experiment was conducted to determine the effect of replacing soybean protein (SBM) with a slow-release urea (SR-U) in control-fed dairy heifers in the tropics. Eight Holstein heifers (237.6±5.45 kg of body weight) were allocated to 2 treatments in a crossover design. Treatments were control (SBM) and SR-U (Optigen II; Alltech Inc., Nicholasville, KY). The forage-to-concentrate ratio was 50:50 [dry matter (DM) basis], and fresh chopped sugarcane was the sole source of forage. Data were analyzed using a mixed-effects model. Compared with the SR-U diet, SBM tended to have greater total tract apparent digestibility of DM and ash. Total tract apparent digestibilities in SBM-fed heifers were greater than in SR-U-fed heifers for organic matter (73.9 vs. 71.3±0.6), crude protein (76.9 vs. 75.2±0.7), hemicellulose (50.5 vs. 43.3±0.9), and starch (98.6 vs. 97.1±0.5). However, total tract apparent digestibility of neutral detergent fiber was similar, and digestibility of acid detergent fiber was higher in SR-U heifers than in SBM (33.3 vs. 27.7±2.6). Water intake and excretion of urine and feces (wet and dry) were similar between treatments. Retained N was similar for all groups, and no differences were observed in the distribution of excreted N. We conclude that when SR-U replaced SBM, it tended to marginally decrease DM and decreased organic matter, crude protein, hemicellulose, and starch total tract apparent digestibility, but did not affect neutral detergent fiber and increased acid detergent fiber digestibility.