Objective: To evaluate the dietary inclusion of neem leaves on the productive and biochemical performance of fattening lambs. Design/methodology: Forty male lambs were assigned according to a completely randomized design. Treatments consisted of dietary inclusion of neem at 0.0, 2.5, 5.0, and 7.5 g kg1 DM for 35 days. Results: The inclusion of neem leaf in the diet did not affect the productive performance (P0.05), while protein and energy metabolites were modified (P0.05). Limitations on study/implications: The bioactive compounds present in neem modified the metabolites related to protein and energy metabolism, although these changes did not reflect improvements in the productive performance. Conclusions: The inclusion of dietary neem (2.5-7.5 g kg1) has no effect on the productive performance, although it does modify some energy and protein metabolites.