All nutrients fall into one of; proteins, fats, carbohydrates, vitamins and minerals

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1 Essential nutrients; - must be supplied to an animal because the animal cannot synthesise them - needed to satisfy the requirements of its cells * if the amount of essential nutrients supplied is insufficient for the requirements of the animal, the animal will become ill Conditionally essential nutrients; - nutrient that must be supplied at certain times because the animal cannot synthesise a sufficient amount for satisfaction of its cells nutrient requirements, eg. during pregnancy, lactation, growth * unlike essential nutrients, conditionally essential nutrients can be synthesised by the animal Other nutrients; - not dietary essentials but are metabolically essential - can be synthesised in sufficient amounts to satisfy the cells requirements Most information on nutrition is about domestic livestock because of its importance to people as well as the lack of opportunity to study others All nutrients fall into one of; proteins, fats, carbohydrates, vitamins and minerals Main functions of nutrients; form structural elements (eg. cell membranes (lipids), bones, etc.,) produce compounds that regulate metabolic processes (eg. enzymes, hormones (proteins, lipids) modify gene expression (minerals) supply energy **energy is not a nutrient, but is derived from nutrients How nutrients are obtained; most obtained by eating food and drinking water sometimes microorganisms within the digestive tract can synthesise essential nutrients *nutrients listed above are absorbed into the animal from the digestive tract occasionally some nutrients are absorbed through the skin or membranes lining the lungs (eg. iodine) Nutritional quality of feed how good is the food at supplying nutrients required by the animal? Based on; - nutrient composition - ease with which it can be digested so the nutrients can be absorbed - how well is satisfies (matches) the requirements of the animal ****different for different animals food might contain lots of nutrients but is of no use if animal cannot digest and absorb them eg. carnivores unable to get sufficient nutrients from fibrous material (which herbivores are able to get sufficient nutrition from)

2 Composition of feed; water Feed dry matter organic proteins, carbohydrates, lipids, vitamins inorganic macro minerals, trace (micro) minerals Other components of feed (not usually considered nutrients); - nucleic acids, organic acids, lignin, toxins, antioxidants Water; - not usually listed as a nutrient, but is essential - most variable component and most easily altered **** For comparison of nutrient composition of different feeds standardise on dry matter basis**** Conversion = concentration of nutrient in fresh food 100 concentration of water 100 *100 concentration of water = dry matter concentration* Quality of feed is affected by; - presence or concentration of; - other nutrients - other compounds, eg. anti-nutritional factors * may interact and affect absorption and metabolism Evaluation of feed quality; chemical analysis animal experiments to determine;

3 - digestibility of feed - how well nutrient matches the requirements the animal Digestibility is affected by; chemical structure of feed and/or the nutrient structure and function of the digestive tract and associated digestive organs digestive physiology, mainly enzymatic processes Importance of digestibility; objective of nutrition get nutrients into cells animal needs to breakdown structure of feed so that nutrients can be released or converted to a form which can then be absorbed across the lining of digestive tract into blood circulation and transported to cells *need to match animal feed to the anatomy and physiology of the digestive tract differences contribute to dietary niches Chemical structure affecting digestibility fibre has the greatest effect on digestibility; Fibre; - composed of carbohydrates (eg. cellulose) and other compounds (eg. lignin) *pasture grasses and legumes contain high concentrations of cellulose problem vertebrate animals don t have enzymes able to digest components of fibre solution herbivores eating fibrous feeds have digestive tracts with an enlarged compartment containing large numbers of microorganisms different bonds between glucose molecules affects digestibility; cellulose; amylose; - no cellulose enzyme not digested - amylase enzyme present by animals enzymes - digested by animals enzymes *Symbiotic relationship between microbes and host*

4 Classify animal species by structure and function of digestive tracts; fermenters cattle, sheep, kangaroos, horses non-fermenters (aka monogastric) dogs, cats, lorikeets *however, the role of microbes in gut of non-fermenters is being recognised as important (eg. immune function) **some non-fermenters have enlarged large intestine and house microorganisms (eg. pigs, chickens), but the bulk of feed is digested without microorganisms fermenters can be further classified based on where enlargement (and microbes) is fermenters foregut fermenters enlargement is before the small intestine (stomach enlarged) sheep, cattle, kangaroos hindgut fermenters enlargement is after the small intestine (colon & caecum enlarged) horses Impact of location of microbes (before or after); microbes synthesise essential nutrients not much opportunity for absorption after the hindgut foregut fermenters more efficient *most efficient foregut fermenters are ruminants cattle, sheep, antelopes process; swallow microbial fermentation eructation (regurgitation) chewing cud (cycle repeats) rumination causes plant material to be broken down to smaller particles which are more easily and efficiently degraded by microbes * foregut of ruminants is more complex than non-ruminant foregut fermenters eg. kangaroos have sacculated foregut (rather than separate chambers) Fermentation reactions; - degrade fibrous feeds and produce energy that can be used by the animal - degrade and re-synthesise proteins - degrade and re-synthesise lipids ****not always a good thing - no control over amino acids synthesised - may have to protect protein from degradation *for all animals the structure and function of the digestive tract influences type of feed eaten (and vice/versa)* amino acids are essential nutrients nectarivores (eg. lorikeets); - eat nectar, which is low in protein - don t digest protein well need food with free amino acids = nectar adapted to dietary niche where efficient protein digestion is not needed ** proteins not absorbed undigested must be broken down to amino acids for absorption ** Digestibility of nutrients in a feed; - is the proportion of a feed or nutrient absorbed from the digestive tract (aka assimilation) - varies with species and structure of feed

5 digestibility = nutrient intake nutrient in faeces nutrient intake Nutrient intake = total amount of nutrient in the feed eaten nutrient in faeces = total amount of nutrient present in faeces after digesting feed and absorbing nutrients Must define what nutrients are for; - maintenance - growth - reproduction - lactation - egg production - work * also affected by other factors such as temperature (eg. using energy to keep warm) Maintenance requirement amount of nutrient required to replace inevitable losses (aka obligatory or endogenous losses) associated with staying alive Inevitable losses result from; - normal metabolic turnover of nutrients in the body - replacement of worn out cells - keeping cells alive Nutrient loss from the body through faeces, urine, skin/hair/nails, sweat Animals are at maintenance when; - body composition is constant - no work is done (except that for survival, eg. obtaining food, water, shelter) - no production is occurring (eg. growth, milk/egg production, feather replacement) List of nutrient requirements should state the purpose for which it should be used, eg. growth of young animal, milk production, work/athletic performance, climatic conditions Nutrient intake v. Nutrient output; if nutrient intake = nutrient output no gain & no loss zero balance okay if adult if nutrient intake > nutrient output increase of nutrient in body positive nutrient balance okay if growing, pregnant if nutrient intake < nutrient output loss of nutrient from body negative balance only okay if overweight The variation in ability of individual animals to digest, transport nutrients affects requirements feeding standards takes into account individual variation in requirements between individuals (*nutrient composition of feed may also vary) Feeding standards; - requirements follow a normal distribution - set at mean + 2SD 97.5% get sufficient nutrients - may be better to have 2.5% getting insufficient adding more (eg. +3SD) may cause toxicity in those animals with lower nutrient requirement ****not usually used for setting energy requirements (mean is used instead) so individuals do not become overweight****