Food intake in monogastric animals

The short-term control of intake in the fowl does not seem to be influenced to the same extent by blood glucose or other nutrients, and it appears that signals are received directly from the crop, as is explained later. 

The senses of sight, smell, touch and taste play an important role in stimulating appetite in man and in influencing the quantity of food ingested at any one meal. It is a common assumption that animals share the same attitudes to food as man, but it is now generally accepted that the senses play a less important role in food intake in farm animals than they do in man. 

Leptin also has direct effects on a number of other factors influencing animal production. For example, leptin reduces fat deposition in adipose tissue, where it suppresses the expression of acetyl-CoA carboxylase, the rate-limiting enzyme involved in fat synthesis. Leptin also has direct effects on the reproductive system, where it induces the release of follicle-stimulating hormone and lutenising hormone from the anterior pituitary. Its effects on reproduction and embryonic development are broad and include factors such as inducing puberty, especially in thinner animals, and shortening the interval from parturition to oestrus. 

The term palatability is used to describe the degree of readiness with which a particular food is selected and eaten, but palatability and food intake are not synonymous. Palatability involves only the senses of smell, touch and taste. Most domestic animals exhibit sniffing behaviour, but the extent to which the sense of smell is necessary in order to locate and select foods is difficult to measure. A variety of aromatic substances, such as dill, aniseed, coriander and fenugreek, are frequently added to animal foods. The inference is that the odour from these spices makes the food more attractive and hence increases intake. Although transitory increases in food intake may occur, the effects of these additives have yet to be convincingly demonstrated to be long-lasting in terms of overall increased food intake. 

Similarly, with the sense of taste, most animals show preferences for certain foods when presented with a choice. Typical is the preference of yoimg pigs for sucrose solutions rather than water. The fowl is indifferent to solutions of the common sugars but finds xylose objectionable, and it will not ingest salt solutions in concentrations beyond the capacity of its excretory system. Every species studied has shown considerable individual variability for example, in a litter of pigs tested with saccharin solutions of different concentrations, some animals preferred high levels of the sweetener whereas others rejected them. 

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