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FLAVOURS & FEED INTAKE IN ANIMAL NUTRITION By Luis Mesas Mora, NOREL S.A.


Flavours as feed additives are still not well understood, mainly due to their subjective character; they are products that don’t just need to satisfy the animal but also the farmer, distributor and manufacturer. For the manufacturer, the usefulness of any given flavour has been focused mainly as part of marketing and image - to be better accepted by the farmer - leaving almost as an afterthought the fact that the main function of a flavour is to optimize feed intake of the animal by olfactory stimuli and taste, prompting a feeling of well-being that will remain etched in the animal’s memory in future visits to the feed trough. While animals, like man, eat because they are hungry, not all


have the same food intake response. Raw materials (source, quality, palatability, smell etc), the incorporation of drugs, fat and even the manufacturing process itself can affect and alter the intake to such an extent that the animal eats only the minimum needed for maintenance. To develop a suitable flavour, we must study all the factors that influence whether intake could be higher or lower.


HUNGER & APPETITE The physiology of eating behaviour begins with hunger and ends when that hunger is satisfied; this satiation could be either physical or metabolic.


HUNGER This can be defined as a state of alert to the need to meet standard nutrient requirements; the physiological stimulus is twofold: - Quantitative energy demand


- Qualitative need (amino acids, vitamins etc)


APPETITE While hunger is to be understood as a sense of craving or urge to eat, the appetite is the anticipated enjoyment of eating; this is produced by the smell, taste and appearance of the feed. Feed that looks,


TABLE 1: PRINCIPAL STIMULI OF DIGESTIVE JUICES TYPE SALIVA GASTRIC PANCREATIC


PRINCIPAL FACTORS OF SECRECION 1. cephalic reflexes


2. oesophago-salivary reflex 1. gastro cephalic reflexes


Stimulation of gastrin secretion and HCl 2. duodenal GIP secretion: gastric secretion inhibitor


1. nervous transmission via vagus nerves 2. duodenal hormones, secretin pancreozymin


ENZYMES - Salival amylase


- Pepsinogens activated in pepsin - Gastric lipase


- Rennet in suckling animals


- Chymotrypsinogen activated in chymotrypsin. - Trypsinogen activated in trypsin. - Carboxypeptidases A and B.-Elastase. - Aminopeptidase. - Pancreatic Amylase. - Pancreatic lipase (activated in the presence of colipase and bile). - Cholesterol. - Stearase. - Pancreatic nucleases. - Deoxyribonucleic acid (DNase). - Ribonuclease (RNase)


INTESTINAL Mechanical stimulation of the intestinal wall


- Proteases. - Maltase. – Sucrase - Lactase. - Lipase


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smells and tastes better will be consumed more avidly and in greater quantity than one without these qualities even if both feeds have the same nutritional value.


STIMULATION OF HUNGER AND SATIETY Hunger and satiation are governed by the hypothalamic centres through nerve stimulation (precedent from the whole digestive system) and hormonal stimulation. These can be divided into: - Taste and smell stimulation ending in bulbar centres; these are connected with amygdaloidal nuclei where the memory circuits are found. This is how the information coming from the nose and mouth will be evaluated - and contrasted with past experiences - and will leave ‘a sign’ for the future. - Gastrointestinal taste receptors. - Peripheral data transmitted via the nervous system (pneumogastric or vagus nerve). Several gastrointestinal peptides can thus serve as messengers of satiety (cholecystokinin, bombesin).


DIGESTIVE FUNCTION Motility and secretory functions of the digestive tract are closely controlled by the nervous system and gastrointestinal hormones. Nerve regulation is ensured mainly by the vagus nerve in three phases: cephalic, gastric and intestinal. The relevant stimuli (see Table 1) may be unconscious mechanical or chemical action on the intestinal wall, or conscious (cephalic), with the involvement of the sensory organs (taste, smell, sight, touch). Thanks to Pavlov’s experiments we distinguish two types of reflex: conditioned and unconditioned. We can distinguish different stages in the digestive function, four phases: Oral, Gastric, Duodenal, Intestinal


ORAL DIGESTION Digestion begins even before the feed is present in the mouth: sensory factors such as smell and sight stimulate saliva production; then, once


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