The fermentative conversion of poultry, swine and cattle feedlot waste filtrates (PWF, SWF and CWF, respectively) into nitrogen-rich feed supplements for ruminants was investigated. Unsupplemented or cheese-whey supplemented waste filtrates were fermented either individually or in 1:1 combination with each other at 43°C. Indigenous flora served as the inoculum. Ammonium hydroxide was automatically added to the fermentor to maintain pH at 7·0. Ammonium hydroxide addition was a function of organic acid production and was responsible for the increase in total nitrogen content in the fermentation product. The ammonium hydroxide neutralized the fermentation acids produced and formed ammonium salts of organic acids, which have been shown to be valuable as nitrogen supplements for ruminant animals. Fermentation of unsupplemented waste filtrates resulted in little change in total nitrogen content but ammonia nitrogen concentration increased 8·3-fold during PWF fermentation, suggesting transformation of urea and uric acid nitrogen to ammonia nitrogen. Fermentation of cheese-whey supplemented PWF, SWF and CWF resulted in products containing 62%, 47·4% and 72% crude protein (total nitrogen × 6·25), respectively, on a dry basis; ammonia nitrogen, respectively, accounted for 63%, 53% and 66% of the crude protein. Lactate and acetate were the major acids in fermented PWF (73% and 20%, respectively), whereas lactate, acetate, and propionate (30%, 29% and 26%, respectively) were the predominant acids in fermented SWF. Fermentation of cheese-whey supplemented PWF + SWF and PWF + CWF resulted in products containing, respectively, 51·6% and 56·7% crude protein; ammonia nitrogen accounted for 81% and 61% of the crude protein, respectively. Lactate, acetate and propionate were the major acids (54·5%, 24·5% and 15·7%, respectively, of the total acids produced) in PWF + SWF fermentation. In the corresponding PWF + CWF fermentation, the same acids accounted for 69%, 21% and 8% of the total acids produced, respectively. In all fermentations, use of the added lactose was >90% within 8 h and >90% of the carbon from lactose was recovered in the organic acids produced. These results indicate that ammoniated organic acid fermentation of livestock wastes, combined with a readily metabolizable carbohydrate waste, is a rapid and efficient means of recycling livestock wastes into nitrogen-rich products, potentially useful as feed supplements for ruminants.