This study investigated the effects of replacing processed Daniellia oliveri seed meal (PDS) for groundnut cake (GNC) in the concentrate diets of Yankasa male lambs (6 months old, body weight of 13.70 ± 0.1 kg (body weight)) on feed intake, rumen fermentation parameters and microbial population. Four diets were formulated to contain 0, 50, 100 and 150 g//kg PDS to replace 0, 25, 50 and 75% GNC (dry matter (DM) basis) in a complete randomized design with five animals per diet. Total DM intake (g/kg BW0.75), ruminal volatile fatty acids, valerate and fungal population linearly increased but ruminal NH3-N, acetate, acetate: propionate, methane production and Entodinium (as % of the total protozoa count) linearly decreased with increasing PDS level (P<0.01). Whereas, intake of concentrate, total DM (g/d and g/kg BW), average daily weight gain, ruminal pH, butyrate, iso-valerate, total bacterial count, proteolytic and amylolytic bacterial counts increased linearly and quadratically, basal roughage intake, protozoal count, cellulolytic bacterial count, methanogen count, Diplodinium and Holotrichs (as % of the total protozoa count) decreased linearly and quadratically (P<0.05) with increasing PDS level. Feed conversion was lowest (L and Q:P < 0.01) for PDS15. Ruminal Ophryoscolex (as % of the total protozoa count) was lower (Q:P < 0.0001) for PDS15 than for other diets. Dietary inclusion of 150 g/kg Daniellia oliveri seed meal to replace 75% DM of groundnut cake in the diet of Yankasa lambs improved intake, rumen fermentation and microbial ecology and weight gain.
