The Principles Underlying Choice Feeding Behaviour in Fowls—with Special Reference to Production Experiments

SummaryThe evidence is now strong that domestic fowls, like other animals, can select a diet which provides them with all the nutrients necessary for maintenance, growth and production. Theoretical models suggest that, compared to the feeding of a standard complete diet, there should be a gain in efficiency in a flock on a self-selection regime, because individuals at different levels of production can select diets appropriate to their requirements. Studies in which these relationships have been investigated have, however, yielded variable results. Egg production in layers or growth in broilers was generally similar in birds on self-selection regimes or on complete diets, but, depending on the study, food utilization efficiency was inferior, similar or superior for reasons which were not immediately clear.In broilers receiving a choice btween two diets which varied in protein content there was some evidence that the lower level of protein intake was set by requirement, but that the upper level was set by the palatability of the higher-protein diet. In laying experiments, generally concerned with calcium selection, intake was usually well-matched to requirements, production was good and food intake was similar or, on occasion, lower.In both types of investigation it was clear that metabolic and nutritional requirements were not the only factors governing selection, and there were some experiments in which a self-selection regime yielded poor results. Behavioural responses concerned with the relative palatability of the diets offered, the learning rate and previous experience of the birds, social factors and even trough position may all affect the results of a study.The development of high-yielding hybrids has produced animals with demanding nutritional requirements, and insofar that nutritional regulation and control systems are inherited and there has been no genetic selection pressure to develop them, these control systems may not be adapted to meet requirements at the highest production levels.