There are many books that directly or indirectly address the subject of veganism and animal welfare. Here are just a few (more to come):

Eat Like You Care – An Examination of the Morality of Eating Animals
Gary L Francione & Anna Charlton (it’s from this book that I have the figure of 57 billion)

Mind if I Order the Cheeseburger? – And Other Questions People Ask Vegans
Sherry F Colb

Both the above books are written by lawyers, and make a very clear and well-reasoned argument. It’s difficult to read them and still be persuaded that eating meat is OK.

The World Peace Diet
Dr Will Tuttle

Animals as Persons: Essays on the Abolition of Animal Exploitation
Gary L Francione

Animals and the Moral Community: Mental Life, Moral Status, and Kinship
Gary Steiner

THE ETHICS OF WHAT WE EAT: Why Our Food Choices Matter
Peter Singer and Jim Mason

Eating Animals
Jonathan Safran Foer

Farmageddon: The True Cost of Cheap Meat
Philip Lymbery

Why We Love Dogs, Eat Pigs, and Wear Cows: An Introduction to Carnism
Melanie Joy

The PETA Practical Guide to Animal Rights
Ingrid Newkirk

Beasts – what animals can teach us about the origins of good and evil
Jeffrey Moussaieff Mason

The Pig Who Sang To The Moon
Jeffrey Mason

The Vegan Cook & Gardener: Growing, Storing and Cooking Delicious Healthy Food all Year Round
Piers Warren and Ella Bee Glendining

Ecological Ethics
Patrick Curry
In-depth exploration of the many aspects of, loosely, the green movement

Toward a Transpersonal Ecology – developing new foundations for environmentalism
Warwick Fox
Written in 1990, this book is still relevant; it examines our human-centred approach to the world and offers a different perspective