Welcome to the next lecture in Leaning Unit 3 where you will learn about the importance of nutrients in animal life I am Dr Peter Ferket and this lecture is about Feeding Behavior and Regulation of Feed Intake In the previous lectures of unit 1 and 2 you learned about what is normal about digestive physiology how nutrients are absorbed and metabolized and ending with energy metabolism In this lecture you will learn about how digestive physiology and nutrients affect feeding behavior and food intake 1 Feeding Behavior and Digestive Tract Physiology in Animals are Closely Interrelated There are three major types of animal feeding behavior Foods normally consumed by animals are those they are capable of digesting 1 2 3 carnivorous omnivorous herbivorous The figure to the right illustrates these three feeding behavior categories along with examples of animals in each 2 Carnivores such as cats are adapted to a meat based diet and require a high quality highly digestible source of nutrients Carnivores mammalian avian reptilian have simple digestive tracts with little microbial activity They may require certain nutrients such as preformed vitamin A some fatty acids and taurine that in the wild can be obtained only from consumption of meat and viscera At the other end of the spectrum herbivores are animals that normally consume only plant material and have a more complex digestive tract with symbiotic microbial activity that permits the digestion of plant fiber Herbivores include Intermediate feeders and non ruminant herbivores such as horses and the ruminants categorized as bulk and roughage eaters concentrate selectors rabbits Omnivores are less fastidious in their feeding behavior than carnivores and herbivores They consume a wide variety of animal and plant foods Pigs poultry racoons apes and people are good examples of omnivores The regulation of feed intake and appetite is a complex subject as it is affected by many different nutritional and physiological factors But one thing is sure water consumption is a primary factor for most animals Maximal feed intake can be achieved only with free choice water available When water is restricted feed intake is reduced If a group of animals goes off feed the first thing to check is the water supply Large amounts of water are required to moisten food in the gut especially in herbivores Ingredients with high water absorbing properties such as bran increase the water requirements As discussed in the lecture about water as a nutrient the amount of water that an animal needs to consume depends on the moisture content of their food and the nutrient composition and osmotic property of the diet The graph to the lower right depicts the daily water to feed ratios in broiler chickens as they grow older Notice the that the amount of water to weight of feed is about 2 1 when they are young and small but then decreases linearly as they grow older Water Feed consumption ratio is not constant because it depends on the nature of the feed provided environmental temperature and the physiological state of the animal In general small animals drink more water relative to the amount of feed they eat because they have a greater body surface area relative to body size that subject to evaporative losses than larger animals 6 Here is another study by Burgos and others that illustrate feed Intake of Lactating Dairy Cows During Baseline 25 and 50 Drinking Water Restriction relative to baseline and rehydration Notice the significant drop in feed intake when water intake was restricted by 25 of ad libitum baseline and more so by 50 of ad libitum water intake Upon rehydration feed intake quickly rebounds to baseline levels and a bit faster in the treatment that received the least amount of water restriction 7 Palatability and Feed Preference Dietary Energy Level Protein and Amino Acid Concentration Other than water intake here is a top 10 list of factors that can affect feed or food intake that I will discuss in more detail later in this lecture These factors are 1 2 3 4 Minerals 5 6 7 8 9 Metabolic Body Size 10 Other Factors Forage Composition Environmental Temperature Pregnancy and Lactation Learning and Conditioning All animals use sensory cutes to seek food ingest food and know when they have enough to eat There are 3 major sensory factors that influence feed intake Food recognition food prehension and ingestion and gastrointestinal activity post ingestinal senses 9 Food recognition is essential for an animal to distinguished food from what is not food Color preferences and shape characteristics are important visual cues Birds have a bimodal color preference orange and blue Hess 1956 Green color is preferred over red by chicks and turkeys Most mammals can see blue green and yellow light but not red Most animals are visual kinesthetic learners They associate positive visual tactile gustatory stimuli Many herd flock or pack animals are social eaters Animals eat when they see others do the same Monkey see monkey do Solitary animals don t follow 10 this norm and tend to be ambush hunters or live in very close proximity to their food I would say humans are definitely social eaters 10 Once food is prehended by the mouth and ingested there are three types of sensory mechanisms that helps the animal distinguishes food Mechanoreceptors thermoreceptors and chemoreceptors Mechanoreceptors senses shape and texture Thermoreceptors detect the food temperature Birds respond to cooling of surface of beak and oral epithelium they have no warm receptors Gentle 1985 Two types of thermoreceptors are known in mammals those activated with warm or hot temperatures range 27 52 C and can perceive harmful and non harmful heat and those whose activation threshold depends on cold stimuli range 17 25 C Chemoreceptors detect taste and they are clustered into taste buds located in areas of contact with food Chickens have about 350 tastebuds cats about 500 dogs about 1700 pigs about 14 000 and cows about 25 000 Just imagine what a thrill a dairy cow would taste chewing her cud As a reference the average person has about 10 000 taste buds and 11 they get replaced every 2 weeks But as a person ages some of those taste cells don t get replaced An older person may only have 5 000 working taste buds That s why certain foods may taste stronger to you than they do to adults These chemoreceptors can detect deficient nutrients Mammals respond to flavored foods but birds only weakly 11 Palatability is a