A total of 40 male guinea pigs (462.0 ± 9.3 g body weight) were divided into four equal groups and fed a basal diet consisting of concentrate mixture (ground maize grain (30.5%), Bengal gram (25%), wheat bran (24%), soya bean meal (18%), mineral mixture (2%; without selenium (Se)), common salt (0.5%) and ascorbic acid (0.05%)) and 10-20 g of available green fodder. While group 1 was fed basal diet alone, without any Se supplementation, groups 2, 3 and 4 were supplemented with 150 ppb of Se, as nano-Se, sodium selenite and organic Se, respectively, for 70 days. Results revealed that the serum Se levels significantly (P