The international thoroughbred racing industry is increasingly vulnerable to public scrutiny due to its horse welfare record. At the same time, the industry is concerned about its sustainability. The interface of welfare and sustainability however offers little for the horses because of a disconnect between dominant conceptions of sustainability and the protection of animals arising from an anthropocentric orientation of most conceptualisations of sustainability. This study investigates the interface of animal protection and sustainability, a realm of great relevance for animal geographies. It develops a theory of interspecies sustainability and applies it to the horseracing industry. The role of one aspect of this theory, naturalness, is explored further as it plays a salient role in the thoroughbred racing and breeding discourse. Nine industry and seven animal advocacy informants in senior roles from Australia, the US and the UK, have been interviewed using semi-structured interviewing and photo-elicitation. Broadly, the two groups’ differences in conceptualising sustainability, welfare and naturalness follow patterns of contrasting worldviews as expressed in reductionism versus holism, techno-bio-medical control of animal bodies versus the protection of animal integrity, and a downplaying and naturalising of violence committed against the horses versus a recognition of the de-naturalisation of the horses’ life-worlds and its impact on them. Eight analytical layers were identified in the intersecting discourse of sustainability and animal protection, of which two have transformational sway to advance interspecies sustainability. This study seeks to raise conceptual awareness to identify at what layers a particular discourse takes place, to unveil industry co-option of the conceptual space of sustainability and animal protection, and to assist animal advocacy and policy development guided by a paradigm of interspecies sustainability for animal protection.