PSX-B-3 - Effect of Infrequent Nitrogen Supplementation on Forage Utilization

Our objective was to determine the effects of differing levels of supplemental nitrogen offered daily, or every 3 d on nitrogen balance, forage intake, and digestibility in cattle consuming low-quality forage. Five ruminally cannulated Angus × Hereford steers (BW = 350 ± 71 kg) were used in a 5 × 5 Latin square design. Steers consumed low-quality bluestem hay (67.7% NDF, 4.7% CP; DM basis) ad libitum. Treatments were no supplement (CON), or cottonseed meal offered at levels providing 120 mg N/kg BW each day (L/1D) or every 3 d (L/3D), 240 mg N/kg BW every 3 d (M/3D), or 360 mg N/kg BW every 3 d (H/3D). Hay, ort, urine, and fecal samples were collected during the last 6 d of each period and ruminal fluid during the last 3 d. Total digestible OM intake was greater in L/1D (6660 g/d; P < 0.01) compared to CON (4498 g/d) and increased linearly in steers supplemented intermittently (5145, 6170, and 6698 g/d for L/3D, M/3D, and H3/D, respectfully; P < 0.01). Total tract OM digestibility was similar between CON and L/1D, L/3D, and H/3D (58.21, 61.21, 60.82, and 60.91%, respectively; P ≥ 0.10) but was greater in M/3D steers (63.30%; P ≤ 0.02). Reducing frequency of protein supplementation to every 3-d improved forage intake and utilization similar to daily supplementation when provided at medium (240 mg N/kg BW) or high (360 mg N/kg BW) levels. Improved efficiency of nitrogen recycling likely buffered disruptions in protein supply, maintaining intake and digestibility of low-quality forage without daily supplementation. Supplementation of protein every 3 d at 240 g N/kg BW appears to the most biologically effective strategy, increasing intake of LQF and maximizing OM digestibility and N utilization.