Aim of this study was to assess the effects of graded levels of dietary protein on scrotal circumference,liveweight changes, semen characteristics, gonadal and extragonadal sperm reserves and serum testosterone profile in Yankasa rams. Fifteen rams were used in this study aged 19.06 ± 2.4 months and weighing 19.4 ±1.6 kg with body condition scores of 3.5. They were divided into three treatment groups (A, B and C) based on dietary protein level. Groups A, B and C received 10%, 15% and 20% crude protein respectively. The rams were managed under intensive system, kept in separate pens, fed individually and allowed two weeks adjustment period. All rams were fed a basal diet of hay (Digitariaspp) ad-libitum and given a supplement ration of concentrate mixture at 2% body weight/day. Body weights and scrotal circumference were recorded weekly. Semen samples were collected weekly for analyses using battery controlled electro ejaculator. Three rams from each group were sacrificed for determination of gonadal and extragonadal sperm reserves. The overall mean scrotal circumferences obtained through the study period for the groups revealed significant (P < 0.05) difference in the increase between group A and B with values of 22.9 ± 0.6 cm and 26.2 ± 0.7 cm. There was also a significant (P < 0.05) increase between group A and C (22.9 ± 0.60 cm and 26.8 ± 0.8 cm) respectively. Rams fed 10% crude protein had significantly (P < 0.05) lower mean live weights (18.8 ± 0.4kg) than those fed 15% (22.1 ± 0.6kg) and 20% (24.1 ± 0.1kg) crude protein. Mean Packed cell volumes obtained in this study revealed rams fed 15% crude protein had significantly (P < 0.05) higher values (31.3 ± 0.9%) than those fed 10% (25.9± 0.7%) and 20% (25.9 ± 0.7%) crude protein. There were no significant (P > 0.05) difference in mean white blood cells counts between all groups. Rams fed 10% had the lowest value of 8.4 ± 0.3 x106/µl as compared to other groups (8.4 ± 0.2 x106/µl and 8.4 ± 0.2 x106/µl). Rams fed 15% crude protein
had significantly (P< 0.05) higher RBC values (5.2 ± 0.11 X106 µl) than other groups (4.2 ± 0.1 X106 µl and 5.1 ± 0.01 X106 µl). Semen concentration was significantly (P < 0.05) higher in rams fed 15% crude protein (163.1 ± 20.6 x106/ml) than group A (96.4 ± 16.3 x106/ml) and group C (98.8 ± 8.5 x106/ml). Motility patterns recorded revealed rams fed 15% crude protein had significantly (P < 0.05) higher values (75.1 ± 3.0%) than group A (54.7 ± 3.8%), and group C (53.9 ± 3.9%). There was no significant difference in reaction time, but rams fed 15% crude protein had the lowest reaction time. Regardless of crude protein levels, left testes weighed more than the right testes. Testicular weights and gonadal reserves were highest in rams fed 20%, but the difference with other groups were not statistically (P > 0.05) different. Regardless of crude protein intake, the corpus epididymis had the lowest reserves, while the cauda had the highest reserves. Rams fed 20% crude protein had the highest abnormalities when compared with those fed 10% and 15% crude protein. This difference was however not statistically (P > 0.05) different. Feeding rams 15 % C.P gave significantly higher values in terms of body weight, scrotal circumference, semen concentration, sperm motility and percentage live sperm, than in rams fed 10 % C.P. From this study,Yankasa rams should be fed crude protein levels of 15% for better reproductive performance. However, studies should also be conducted to investigate if antioxidants could ameliorate some of the effects of low and high levels of protein diets that were observed in this study.