Measuring food intake in farm and laboratory animals.

Abstract

Measurement of food intake in farm and laboratory animals is often relatively easy compared with that of animals and human subjects that are free living, as will be evident from the subsequent papers in the present symposium. There are, however, some circumstances in which intake measurements of farm or laboratory animals still present methodological problems. The first aim of the present paper is to review briefly these problem areas and give recent references that provide a more in-depth discussion of the methodologies concerned. When measuring food intake of farm and laboratory animals we generally have control over the animals as well as the feeds and the environmental conditions. This facilitates the measurement of daily nutrient intake of individual animals with great accuracy. In addition, more and more detailed information on feeding behaviour for much shorter time scales becomes available through the use of automated measuring equipment (for example, see for pigs: Young & Lawrence, 1994; for rats: Madrid et al. 1995; for cows: Tolkamp & Kyriazakis, 1997). A great challenge is the interpretation of the variation in food intake and of feeding behaviour. The present contribution also aims to highlight one of the problems regarding this issue; the relevant time scale for measurement of food intake and its interpretation. In view of our research backgrounds, we hope to achieve this aim by using data from scientific fields that sometimes seem to have developed quite separately. The first field relates to food intake measurements with laboratory animals. The aim of experiments with laboratory animals is generally a better understanding of food intake regulation in mature mammals, with particular emphasis on possible applications to man. The second field relates to food intake and feeding behaviour measurements of mainly growing or reproducing farm animals. A major proportion of this type of data exists because of the economic importance of food intake in animal farming systems. Some of these data result from research aimed at finding solutions to practical problems. However, other data also refer to experiments specifically carried out to test hypotheses with regard to food intake regulation. Thus, these results may also be very useful, not least because of the detail in which nutrient intake and utilization is frequently recorded in farm animals. We will first highlight the apparent flexibility with which farm and laboratory animals adjust their short-term feeding behaviour without compromising their desired food intake level. This raises the question of what it is that animals try to achieve, and on what time scale they attempt to do this, i.e. the search for a functional explanation of feeding behaviour. This approach seems especially relevant in reaching a better understanding of the animal's responses to changes in its food and in its environment, and in arriving at improved predictions of food intake.