3.3 A model of the Growth and Feed Intake of Ad Libitum Fed Animals, Particularly Poultry

Whittemore and Fawcett (1976) and Whittemore (1976) showed how ideas and data from different disciplines could be brought together to simulate, using a computer program, the growth of the pig on controlled feeding. Controlled feeding, as shown in Figure 3.3.1, is one of three types of feeding system (Emmans, 1981). Parks (1970) dealt with systems of the second type, in which animals are given free access to single feed. In such a system, the composition of the diet, but not its amount, is known in advance. Parks (1970) suggested that the rate of feed intake in growing animals increased at a diminishing rate with age towards an asymptotic value; Figure 3.3.2. This function has two parameters — the asymptote and a time constant. The values of these were seen as functions of feed composition, genotype and environment. He went on to predict growth as a function of feed intake and a conversion efficiency. While a description of how ad libitum feed intake changes with age is useful, it is not as powerful as an understanding of what governs feed intake would be. While there are many theories about the mechanisms that animals use to control their feed intake at a given level, there is none that can be used to predict what this level will be. One is proposed in this paper.