Effect of Nitrogen Source On Forage Characteristics and Performance of Cattle Grazing Warm Season Pastures.

Twenty-four crossbred (Bos taurus × Bos indicus) beef steers (bodyweight= 233 kg) were used in the first year of a three-year study to examine the efficacy of nitrogen fertilizer compared with feed supplementation on forage quality, forage quantity, animal production, and nitrogen cycling.  Steers were weighed, and assigned to six 4-ha paddocks (four steers per paddock).  Paddocks were randomly assigned to one of three treatments:  no fertilizer and no supplement; supplement of 1.1 kg of dried distiller’s grains per animal and no fertilizer; or fertilizer and no supplement.  Pastures were warm-season perennials (bermudagrass and bahiagrass).  Cattle were individually weighed every 28 days, and an individual fecal sample was collected.  Pasture clippings were taken weekly and pooled for nutrient analysis for each period.  Data were analyzed using a linear model, with pasture as the experimental unit and treatment as the main effect.  Results indicate that treatment had no significant effect on bodyweight at days 0, 84, or 112.  Supplemental feed increased bodyweight (P = 0.10) at day 56, compared with the other treatments.  Moreover, treatment had no significant effect on average daily gain at any period within the study. Fecal N increased at day 28 (P < 0.05) for supplemented cattle compared with their counterparts, increased at day 56 (P < 0.09) for both supplement and fertilizer groups, and increased at day 84 for the fertilizer group.  Overall fecal N was increased (P <0.08) using either supplement or fertilizer application.  Forage mass did not differ significantly among treatments at any point in the study; however, during the fourth period, ADF was reduced and TDN increased (P < 0.04) by either feed or fertilizer.  While it is too early to make a determination, results suggest that supplementing cattle might improve performance with little effect on N-cycling.