Field experiment was carried out at the Experimental Station Farm in Giza, ARC, Egypt, during 2012 and 2013 seasons to study the effect of varying sources and rates of nitrogen fertilizers on fresh and dry forage yield of sudangrass, chemical constituents, nitrate and nitrite accumulation in plant. It can be recommended that mineral fertilizing sudangrass plants with 100 kg N/fed as ammonium sulphate in order to maximize its forage yields and reduce nitrate and nitrite accumulation in plant under the environmental conditions of Giza Governorate, Egypt. Biological experiment was carried out to investigate the effect of different levels of nitrate in Rex male rabbit diets. In conclusion, rabbits under these investigations can tolerate 0.73% nitrate (1% sodium nitrate) in feed without significant negative effect. Most results of 1.46 % nitrate (2% sodium nitrate) and all results of 2.19 % nitrate (3% sodium nitrate) had toxic effect of growth performance, digestibility of nutrients,blood parameters, histological structure of internal organs of rabbits.