The search for low cost, nutritive ingredients for animal feeds led to consideration of the possible harmful or beneficial effects of secondary plant products. This book summarises the proceedings of a recent MAFF conference held at the University of Reading, and contains overviews of secondary plant products in general, and tannins, trypsin inhibitors and lectins in particular. Attendees were drawn from academia and industry, and included animal nutritionists and plant breeders. In the concluding discussion, an attempt was made to identify future research needs. What emerged was the need to be precise about the identity of the secondary plant product present, and its effects, for better and relevant analyses, and to be mindful of the different needs in the UK of pigs and poultry, compared with ruminants. "This book highlights ways to improve and optimize the use of vegetable protein in animal diets, especially now that animal protein use in animal feeds has been banned in the UK and is greatly limited in the US" - "Feedstuffs". "The very clear presentation with many experimental results makes it an invaluable work for those who are willing to understand these intricate mechanisms and to contribute to improving their effects on animals" - "Livestock Production Science".