Understanding the relationships between short-term feeding behaviour and long-term intake

The prediction o f animal performance under a variety o f conditions has long been a goal within animal science. Because animal performance is a function o f food intake this has to be predicted if performance is to be effectively modelled. Analysis of short-term feeding behaviour may give insight into the regulation o f feed intake allowing better models o f intake to be constructed. This thesis examines in detail the short-term feeding behaviour o f dairy cows to better understand food intake regulation. Feeding behaviour consists of feeding events separated by non-feeding intervals. Feeding events are generally clustered into meals. Chapter 2 describes a methodology that utilises a combination of Gaussian and Weibull distributions to describe the length of intervals between feeding events. This method estimates a meal criterion, which allowes the clustering o f feeding events into meals in a biologically acceptable way. In subsequent chapters short-term feeding behaviour is assessed largely in terms o f meals. Changes in the probability o f animals starting a meal with time since the last meal is thought to give insight into the mechanisms underlying intake regulation. Starting probabilities are often calculated with data pooled across individuals or day and night. The extent to which pooling affects conclusions was assessed by analysing experimental data from cows. Results were used to parameterise simulation models, where the consequences of data pooling were systematically investigated. This showed that as variability in pooled data increases so did the likelihood of misinterpreting results. When offered a choice o f foods, animals are able to select a consistent combination o f these foods in the long-term. Analysis o f how a consistent diet is achieved may give insights into the mechanisms regulating intake. The hypothesis that consistent long-term diet choice may be a consequence of diet selection within meals was tested using probability theory. This showed that cows did not have more meals with a composition that was similar to the long-term average diet choice than expected by chance. Therefore, no evidence was found to support such short-term regulation of diet choice. Analysis in previous chapters suggested methods for exploring short-term feeding behaviour, which had yet to be attempted. These included calculation o f changes in the probability of animals ending a meal with time since the start o f the meal, diurnal patterns o f diet choice and prandial correlations. The hypothesis that such analyses could give insights into mechanisms controlling feeding behaviour was tested. No evidence o f food intake or diet choice regulation in the very short-term was found. The final chapter examined previously published theories o f intake regulation. Predictions from these theories were contrasted with the findings presented in this thesis and in the literature. Theories that advocate regulation in the short-term, and other theories, are identified and discussed in light of current findings. The direction o f future work, to enable successful prediction of intake, is discussed.