The effects of feeding Leucaena leucocephala on semen quality and fertility were examined using four dihydroxy pyridone (DHP)-adapted (21.0, 26.5, 27.0 and 31.0 kg) and four DHP-unadapted (28.0, 31.0, 40.0 and 44.0 kg) South African indigenous Nguni bucks (mature male goats). The DHP-adapted bucks were assigned to air-dried Leucaena leucocephala forage (LL; Leucaena group) while the unadapted ones were maintained on a cereal-based concentrate diet (C; concentrate group) containing 122 g crude protein (CP)/kg over an 84-day period. Buck semen samples were collected on days 0 and 77 of the study. On the last day of the study (day 84), bucks in the Leucaena group were divided into two equal subgroups; a subgroup was assigned to Leucaena leucocephala-grass pasture (LGP) with ten does (mature female goats) while the second subgroup was assigned to natural pasture (NP) with nine does. Similarly, the two concentrate subgroups were separately assigned to mate nine and ten does on LGP and NP plots, respectively. The proportions of normal semen on both groups were not significantly different. However, semen quality on LL treatment increased significantly (P = 0.004) between days 0 and 77 and probably explains the significant (P<0.01) difference between the fertility rates of bucks on both treatments. There was no evidence that feeding LL was detrimental to semen quality and fertility of bucks and to conception among females mated by the bucks fed the forage; perhaps due to the fact that the bucks had adapted to DHP as a result of the DHP-degrading rumen bacteria (Synergistes jonesii) that were transferred to them by the does. Synergistes jonesii is known to be capable of detoxifying mimosine and its toxic metabolites to innocuous compounds.