The efficacy and comparative cost analysis of three injectable ivermectin preparations was evaluated in West African Dwarf (WAD) sheep naturally infected with gastrointestinal nematodes. Three anthelmintics: ivomec classic® (IVC), ivomec super® (IVS) and ivomec gold® (IVG) were administered at a dose rate of 200µg/kg to control gastrointestinal nematodes in three treatment groups comprising five animals each. The faecal egg counts (FEC) for each animal pre-treatment, and thereafter for a period of 16 weeks post-treatment was carried out using the modified McMaster technique. The results is a pre-treatment mean FEC for groups A, B and C of 970±550.36, 880± 279.55 and 1640±893.78 eggs per gram (epg), respectively and a mean FEC of zero for all treatment groups one week post treatment. The mean FEC of zero was maintained for 28, 35 and 56 days, respectively. A mean FEC threshold for re-treatment of 500 epg was exceeded at days 42, 49 and 84 for groups A (615±167.26), B (830±287.49) and C (737.5±448.10), respectively. The results were subjected into a deterministic model to estimate the costs of using IVC, IVS or IVG in an annual control program.