Joshua Evans was a Quaker minister and abolitionist from New Jersey. Evans and his thoughts are representative of a radical, "primitive" Quaker tradition and reflect the diversity of late eighteenth century Quakerism. His papers have been digitized and are available freely. Evans's 1762 journal particularly addresses his inspiration for being a vegetarian and against animal cruelty.
Sarah Norcliffe Cleghorn was a Quaker author, reformer, and pacifist from Vermont, and Philadelphia. She was active in the anti-vivisection movement, as well as other reform efforts for peace, women’s suffrage, anti-lynching, prison reform, and opposition to child labor. Cleghorn's correspondence and writings are available in the Library.
John Woolman wrote about poultry and livestock, particularly on transatlantic voyages. For example, on his 1772 journey to England, Woolman noted that some chickens were ill, while others were carried overboard. He wrote that the “love of God is verily perfected…a care is felt in us that we do not lessen that sweetness of life in the animal creation'. Woolman recommends that lading fewer fowl, and thereby eating less meat, would accord with “pure wisdom.”
Benjamin Lay is most associated with abolition but he was also a vegetarian. You can read more about his vegetarianism and advocacy for animal rights in Marcus Rediker's The Fearless Benjamin Lay: the Quaker Dwarf Who Became the First Revolutionary Abolitionist (2017) and see an image of Benjamin Lay that remarks on his diet.