pity it doesn't give a precise reference; if I have time later I'll see if I can track it down.
Was easier than I thought: "Columella's De Re Rustica (1954) is one of several agricultural works that provide instructions for the care of egg-laying chickens, including housing requirements and modifying feed to make hens lay sooner, more often, and with larger eggs (De Re Rustica, book 8, ch.3, s.1–8; book 8, ch.5, s.1–2). He also describes aspects of productivity and preservation, such as transferring eggs for hatching to capable broody hens, and using chaff, bran and salt for egg storage (De Re Rustica, book 8, ch.6, s.1–2). Columella and other ancient authors, such as Varro, even suggest that certain types of chicken, including those with five toes, were the best for egg-laying and brooding (De Re Rustica, book 8, ch.2, s.8)."
https://doi.org/10.1016/j.jasrep.2017.09.013 page 1010.