This paper examines the discourses and practices of pedigree livestock breeding, focusing on beef cattle and sheep in the UK, concentrating on an under-examined aspect of this – the deselection and rejection of some animals from future breeding populations. In the context of exploring how animals are valued and represented in different ways in relation to particular agricultural knowledge-practices, it focuses on deselecting particular animals from breeding populations, drawing attention to shifts in such knowledge-practices related to the emergence of ‘genetic’ techniques in livestock breeding which are arguably displacing ‘traditional’ visual and experiential knowledges of livestock animals. The paper situates this discussion in the analytical framework provided by Foucault’s conception of ‘biopower’, exploring how interventions in livestock populations aimed at the fostering of domestic animal life are necessarily also associated with the imperative that certain animals must die and not contribute to the future reproduction of their breed. The ‘geneticisation’ of livestock breeding produces new articulations of this process associated with different understandings of animal life and the possibilities of different modes of intervention in livestock populations. Genetic techniques increasingly quantify and rationalise processes of selection and deselection, and affect how animals are perceived and valued both as groups and as individuals. The paper concludes by emphasising that the valuation of livestock animals is contested, and that the entanglement of ‘traditional’ and ‘genetic’ modes of valuation means that there are multiple layers of valuation and (de)selection involved in breeding knowledge-practices.