As the authors say in the Preface, this book represents a lifetime achievement for them built on their years of research, teaching and extension in theoretical and practical nutrition of farm ruminants.

It is, in effect, a commentary on the development of the feed rationing system ‘The Ruminant Nutrition System (RNS)’, which has evolved from the various elements of the Cornell Net Carbohydrate and Protein System (CNCPS) that the authors and many others at Cornell University have developed since the late 1970s.

As a compendium of research publications in the area of ruminant nutrition, the book is impressive. It contains over 2000 references spanning the nineteenth century to the present. They rather serve to highlight the rising tide of activity in this area of science that peaked in the 1980s and 1990s, but which has reduced in volume of output since then. The integration of this growing fund of knowledge into ‘feeding systems’ that are suitable for practical application has punctuated the development of farm ruminant nutritional research at various times over the last century or so. The authors track some of these activities in giving context to their own work and the evolution of the RNS.

All feeding systems depend on sets of rules that allow the amounts and qualities of feeds that are eaten to be matched to the biological demands of the animals that are eating them. So, after a broad introduction to the origins of the RNS/CNCPS and of the place of ruminant animals in the world, the book has major sections on ‘Modeling the Dietary Supply of Energy and Other Nutrients’, ‘Modeling the Animal Requirements for Energy and Other Nutrients’ and ‘Developing the Feed Library’.

The sections on dietary supply and on animal requirements are laced with commentary on background research that has supported various ‘sub-models’ within the overall modelling structure of the RNS. The scope is wide and often reads like a series of mini-reviews of topics that might be covered in a lecture series on ruminant nutrition. Given the authors’ background this is not surprising. At times, though, the commentary somewhat obscures the clarity of the description of the RNS. This would not matter for someone who is using the book as a text-book source on ruminant nutrition, but for those who are interested in the technical detail of RNS it may be frustrating.

The final section on ‘Developing the Feed Library’, together with much useful text in earlier sections on the development of analytical methodology for various nutritionally important characteristics of feeds (and a helpful Appendix), provides an excellent source of reference on feed analytical methods. It is unfortunate, though, that the background and description of chosen methodologies are scattered throughout the book rather than being consolidated.

The vast majority (more than 360 pages) of the text is devoted to ‘energy’ and ‘protein’ nutrition, with a mere 16 pages to cover vitamins and minerals. The advantage of the brevity in dealing with ‘other nutrients’ are that it is crystal clear as to how the RNS deals with these nutrients. The reader has to work much harder to distil from the text just exactly which relationships or systems are included in the RNS and which are presented for comparison.

I was not sure who the likely audience for this book will be. There is certainly plenty of background material that can be educational for undergraduate and post-graduate students with interests in the development of knowledge about ruminant nutrition. For those with a technical interest in the RNS/CNCPS this is certainly not a technical handbook in a conventional sense – and nor was it intended to be. The reader has to be willing to work through a lot of background text to unearth the structural elements of the model. If you are willing to make the effort to read carefully, though, there is plenty to learn about the history and rationale for this feeding system as it currently stands – and with some speculation on developments that are needed for the future.

All models invite criticism – especially from those who were not involved in their construction, or who have developed ‘competitor’ ones. The honest reasoning that is given here for the RNS provides fertile ground for debate. Why, for example, is this (and most if not all other feeding system models) so poorly linked to genotype at a time when genetic and genomic science for farmed livestock is advancing so quickly? One must admire, though, the scale of effort that has been put into building this system and which is documented here.

There is little to show how well RNS works as a practical tool. A section on application would have been an interesting inclusion.

The book is, to an extent, the summary of a career's effort for one of the authors. Does it reflect the height of achievement for this particular modelling approach? Will ‘next steps’ require a different modelling strategy? I was left wondering how a bright new researcher at the start of her/his career in this area would look back on this book when (s)he comes to retire.