This first paper of a series of three critically examines current ideas about the causes of
differences in voluntary feed intake, and particularly roughage intake, in ruminants.
Explanations for such differences have usually been based upon the explicit or implicit
assumption that an animal seeks to obtain a genetically determined maximum growth and
production rate and a therefore required maximum nutrient intake. The frequent failure of
animals to achieve a maximum nutrient intake would be the consequence of constraints …

Part I of this thesis contains a critical appraisal of the commonly accepted theory with regard
to feed intake regulation in ruminants and the presentation of a new theory. This new theory
assumes that feed consumption creates both benefits to the animal (in a non-reproducing
animal the intake of net energy for maintenance and gain) and costs (the total oxygen
consumption of the animal). It is hypothesized that, for the animal, the intake level where the
ratio between benefits and costs becomes maximal, is optimal. Predictions of this optimum …