This report by the FAO examines the important issue of the relationship between biofuel production and livestock: there can be synergies (ie. the use of biofuel co-products as animal feed) and trade offs (such as biofuel production effects on the price of grains).
Trade-offs and synergies need to be considered in the context of land use change, the GHG balance of biofuels and land pressures – ie. the balance between land for fuel, for feed and for food for human consumption.
Each of the chapters has abstracts and they variously cover environmental, economic and nutritional/digestibility (ie. for the livestock) issues for a range of feedstocks, biofuel types, and livestock (including aquaculture). The first chapter provides a useful introdutory overview of the issues while the last one synthesises the discussions in the individual chapters.
Harinder P.S. Makkar H P S (ed) (2012). Biofuel co-products as livestock feed - Opportunities and challenges, FAO, Rome.
The pdf file is available here.