I wouldn't say there are tsetse resistant cattle, more like tsetse tolerant cattle like the ndama. It still affects their size, milk flow, weight and energy levels its just over the years they've become one of the smallest cow breeds, don't produce much milk and don't have as extensive ranges.
It also likely descends from the Bos spp. That existed during the Neolithic Subpluvial or rather from the Sahel or northern mountains/nile that over millions of years adapted to periodic tsetse expansion. No horse species can really claim that much less actually survive in say Central Africa.