Infection. The effect being severe in T. b. brucei but moderate in T. evansi infection and mixed infections which may affect spermatogenesis and male secondary sex characteristics. Seminal plasma ascorbic acid may have considerable role in improving male fertility potential in the control group. Ascorbic acid is present at approximately ten fold higher concentration in seminal plasma as compared to blood and is mostly secreted from seminal vesicles. Depletion of ascorbic acid pool of the host during the infection was postulated as a possible cause of the iron sequestration. Oxidative stress is known to be implicated in a variety of pathophysiological events that cause male infertility. The present study aimed to investigate the effect of T. evansi and T. b. brucei on seminal plasma ascorbic acid and semen quality and its relation to serum free testosterone in Yankasa rams. Sixteen (16) Yankasa rams aged between 24 and 30 months and weighed between 22 to 25 kg were. purchased from Tike market Mubi. They were screened for the presence of endo and ectoparasites. The rams were thereafter treated with Oxytetracycline (Tridax®) intramuscularly, at a dose of 20 mg/kg. Body weight and Albendazole orally, at a dose of 7.5 mg/kg body weight. The rams were sprayed against ectoparasites with Diazinon (Diaznol®, Animal Care, Nig. Ltd.). They were allowed to acclimatized for four weeks and ear-tagged for the purpose of identification in a clean fly proof house, adequately fed and given water ad libitum. By the end of the four weeks acclimatization the rams were randomly grouped into four experimental groups of four rams each, based on their weights. The rams in groups 1, 2 and 3 were experimentally infected with T. brucei brucei,(Emodike strain), T. evansi and mixed inoculum of both parasites, respectively while those in group 4 served as the naive control. Each infected ram received 2ml containing 2x106 trypanosomes via the jugular vein. Each infected ram received 2ml containing 2x106 trypanosomes via the jugular vein. The seminal plasma ascorbic acid was measured spectrophotometrically. Ascorbic acid stock solutions were prepared from L ascorbic acid. The HPLC grade methanol and acetic acid glacial were used. 0.45 µm Millipore solvent filter, was used for all reagent and standard solutions. All samples were vortexed for 20 seconds and cold-centrifuged at 10000 rpm for 3 min. Each supernatant was kept at− 24 C until a 20 µl aliquot was injected onto the HPLC system (Buck scientific BLC 10/11, Las Vegas, USA). Blood was obtained through vein puncture into vaccutainer tubes for serum testosterone analysis. It was then centrifuged at 1500rpm for 5 min and serum obtained was stored at-200C until laboratory analysis was carried out. Serum testosterone was determined using testosterone enzyme immunosorbent assay (ELISA) kit (Diagnostic Automation/Cortes Diagnostic Inc. Immuno Diagnostics CA, Woodland Hills, Califonia) according to the manufacturer’s instructions. Each sample was analyzed in dublicate and absorbance was measured at 450 nm with an ELISA reader (ROBONIK ELISA Plate Analyser, model: Readwell Touch). The seminal plasma ascorbic acid in this study was significantly lower in the infected rams than in the normal control rams. In this study there was increase (higher) semen volume in the infected compare to the control group which could be due to