For introductory presentations see:

Huth, M. (2020). How to Recognize Animals‘ Vulnerability. Questioning the Orthodoxies of Moral Individualism and Relationalism in Animal Ethics. Animals, 10(2), p. 235. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7070496/ 

Zuolo, F. (2020). Views on the Moral Status of Animals. In F. Zuolo (Hrsg.), Animals, Political Liberalism and Public Reason (S. 129–181). Springer Nature. https://link.springer.com/chapter/10.1007/978-3-030-49509-1_4#Sec3

For selected relationalist approaches see, among others:

Adams, C. J., & Donovan, J. (1995). Animals and Women. Feminist Theoretical Explorations. Duke University Press.

Midgley, M. (1983). Animals and Why They Matter. A Journey Around the Species Barrier. University of Georgia Press.

Palmer, C. (2010). Animal Ethics in Context. Columbia University Press.

Palmer, C. (2011). The Moral Relevance of  the Distinction between Domesticated and Wild Animals. In T. L. Beauchamp & R. G. Freys (Eds.), The Oxford Handbook of Animal Ethics (pp. 701–725). Oxford University Press.