Influence of polymer-coated slow-release urea on total tract apparent digestibility, ruminal fermentation and performance of Nellore steers

Objective Two experiments were performed to evaluate the effects of coated slow-release urea on nutrient digestion, ruminal fermentation, nitrogen utilization, blood glucose and urea concentration (Exp 1), and average daily gain (ADG; Exp 2) of steers. Methods Exp 1: Eight ruminally fistulated steers [503±28.5 kg body weight (BW)] were distributed into a d 4×4 Latin square design and assigned to treatments: control (CON), feed grade urea (U2), polymer-coated slow-release urea A (SRA2), and polymer-coated slow-release urea B (SRB2). Dietary urea sources were set at 20 g/kg DM. Exp 2: 84 steers (350.5±26.5 kg initial BW) were distributed to treatments: CON, FGU at 10 or 20 g/kg diet DM (U1 and U2, respectively), coated SRA2 at 10 or 20 g/kg diet DM (SRA1 and SRA2, respectively), and coated SRB at 10 or 20 g/kg diet DM (SRB1 and SRB2, respectively). Results Exp 1: Urea treatments (U2+SRA2+SRB2) decreased (7.4%, p = 0.03) the DM intake and increased (11.4%, p<0.01) crude protein digestibility. Coated slow-release urea (SRA2+SRB2) showed similar nutrient digestibility compwared to feed grade urea (FGU). However, steers fed SRB2 had higher (p = 0.02) DM digestibility compared to those fed SRA2. Urea sources did not affect ruminal fermentation when compared to CON. Although, coated slow-release urea showed lower (p = 0.01) concentration of NH3-N (−10.4%) and acetate to propionate ratio than U2. Coated slow-release urea showed lower (p = 0.02) urinary N and blood urea concentration compared to FGU. Exp 2: Urea sources decreased (p = 0.01) the ADG in relation to CON. Animals fed urea sources at 10 g/kg DM showed higher (12.33%, p = 0.01) ADG compared to those fed urea at 20 g/kg DM. Conclusion Feeding urea decreased the nutrient intake without largely affected the nutrient digestibility. In addition, polymer-coated slow-release urea sources decreased ruminal ammonia concentration and increased ruminal propionate production. Urea at 20 g/kg DM, regardless of source, decreased ADG compared both to CON and diets with urea at 10 g/kg DM

Existing and emerging cyanocidal compounds: new perspectives for cyanobacterial bloom mitigation

To help ban the use of general toxic algicides, research efforts are now directed towards the discovery of compounds that are specifically acting as cyanocides. Here, we review the past and look forward into the future, where the less desirable general algicides like copper sulphate, diuron or endothall may become replaced by compounds that show better specificity for cyanobacteria and are biodegradable or transform into non-toxic products after application. For a range of products, we review the activity, the mode of action, effectiveness, durability, toxicity towards non-target species, plus costs involved, and discuss the experience with and prospects for small water volume interventions up to the mitigation of entire lakes; we arrive at recommendations for a series of natural products and extracted organic compounds or derived synthetic homologues with promising cyanocidal properties, and briefly mention emerging nanoparticle applications. Finally, we detail on the recently introduced application of hydrogen peroxide for the selective killing of cyanobacteria in freshwater lakes