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ANUT 300-500: Animal Nutrition

Revision Notes

ANUT-300-500 was originally issued in 2008. It was created with funding provided by the Sheep CRC supported by MLA and AWI.

The module was revised in 2012. The revision increased the number of topics from 27 to 32, three of these being topics related to the nutrition of companion animals.

The topics are now organised into 5 modules.


Module 1: Theory and Practice of Animal Nutrition

On completion of this topic you should be able to:

  • Describe the major components of diets for livestock: energy and nutrients
  • Explain the importance of ‘anti-nutrients’

All living animals, and indeed the cells they are made of, have the same basic requirements for energy, protein (as amino acids), minerals, vitamins and water.  There is considerable confusion when the terms ‘energy’ and ‘protein’ are used in discussing feeds and their nutritive value. For all animals, and especially ruminants, feeds cannot provide purely ‘energy’ or ‘protein’. All sources of protein can contribute in some way to the energy metabolism of the animal. In ruminants, even sources of purified carbohydrate, containing no protein as such, provide a source of energy for rumen microbes to grow and the microbes then supply additional protein and amino acids to the host animal. We have lectures that focus on ‘energy’ and ‘protein’ and, from what has just been said, this may seem inappropriate. However, there are some feeds that do provide more energy relative to protein than other feeds. Conversely, there are feeds that provide more protein relative to energy. Such sources are referred to as ‘energy’ and ‘protein’ concentrates. It is important not to think in terms of absolutes when it comes to defining feeds as sources of energy or protein. Most protein and energy concentrates will also provide vitamins, minerals and small amounts of water.

Topic 1: What are the Major Nutrients

All living organisms, and indeed the cells they are made of, have the same basic nutritional requirements: they are energy, protein (as amino acids), minerals, vitamins (and water). Even microbial cells in the rumen have these basic requirements. Animals (and people) also have a requirement for certain long chain fatty acids that their body cells cannot synthesise. The amount of each nutrient needed is called the nutritional requirement. Requirements vary between individuals and at different stages of life for each individual.

Topic 2: Energy Requirements

Animal feeding management is about matching feeds with needs. The feed energy that an animal has available for tissue metabolism determines, firstly, whether it can survive, and secondly, how much of the various animal products it can produce. The feed energy available to tissues is expressed as metabolisable energy (ME). Sources of ME include lipids, glucose and VFA. In practice, the first call on the ME is to supply maintenance energy (MEm). This is the energy required just to keep the animal alive and functioning but not growing, lactating or reproducing. The longer an animal lives, the more non-productive energy it uses.

Topic 3: Digestible and Metabolisable Energy

The commonly used unit of energy is the megajoule (MJ) although the ‘calorie’ is also used. One calorie is the amount of energy required to raise the temperature of 1 ml of water 1 degree Celsius and 1 MJ equals 4128 calories or 4.182 kcal. All living cells require energy to maintain their integrity and to grow and produce secretions and so on. Only chemical energy can fulfil cellular needs and this is provided by the organic materials an animal ingests. (The energy in organic matter comes from solar energy trapped by photosynthesis in plants.) Energy cannot be created or destroyed – so the energy ingested can be accounted for by adding that excreted to that retained in tissues and that converted to heat. The energy stored chemically in organic materials (the Gross Energy, GE) is released as heat if the material is completely oxidised in cells or combusted in an oxygenated atmosphere.

Topic 4: The Interactions between Energy and Protein

All animals require protein as well as energy for their survival (maintenance). They need additional amounts of protein to deposit tissue to grow or produce milk and wool. Growth of cells and tissues involves the synthesis of protein (from amino acids), as well as carbohydrates (from simple sugars) and fats (from other fats, and sugars, and proteins). Thus animals need the building monomers to grow and reproduce; and they cannot grow and reproduce unless all the necessary building monomers are available in their cells and tissues. But they also need chemical energy (ATP) to create the chemical bonds between the monomers that hold the polymers together. By analogy, the synthesis is like building a brick wall (polymers) using bricks as the building material (monomers) and mortar (chemical bond energy) to hold the bricks together.

Topic 5: Supplying Protein for Ruminants

In order to provide effective protein nutrition for the animal, it is essential that we understand:

  • The requirements of the animal tissues for amino acids;
  • The amino acid losses during digestion, absorption and metabolism
  • The amount and quality of protein provided in the feed; and
  • For ruminants, the amount and quality of protein provided by rumen microbes

Topic 6: From Feed Components to Milk, Meat and Wool

Because this Unit deals with the practical application of nutrition, its focus is on feeding management as a means of optimising feed inputs and production outputs. This means we want to manage the feeding of our animals to optimise saleable outputs such as egg, meat, milk, wool, and skins. We also want to feed our breeding stock efficiently to obtain optimum reproductive performance and replacement animals for our flocks and herds. Draught animal power is also an important output from production systems in some countries. Management of animals to achieve optimum input/output is helped by an understanding of the biochemistry in cells that is responsible for the breakdown of polymers to simple monomers, and their re–synthesis into similar, but subtly different polymers.


MODULE 2: Animal feeds – Matching feeds with needs

On completion of this topic you should be able to:

  • Develop an understanding of the computer-based and manual approaches to formulating diets.
  • Students are encouraged to try a range of software packages, therefore an ability ‘navigate’ the software environment of nutrition and diet formulation packages is an important learning objective. The ability to adapt to and use new diet formulation software is an essential skill for any nutritionist today.

With the ingredients selected and evaluated, the next step is to put the information into a formula that will calculate the required diet. This can be done using manual calculation, spreadsheet programs or least–cost formulation computer software packages. Diet formulation is not a simple matter and is best be left to qualified nutritionists. Essentially, it is a process that matches the nutrient requirements of the animal with the nutrients present in available ingredients. It must consider not only the many individual nutritional components, such as energy, amino acids, minerals and vitamins, but also ensure that important ratios, such as energy:amino acids and calcium:phosphorus are maintained within an acceptable range. The process should provide safety margins that avoid unwanted surprises, while at the same time avoiding costly over–formulation. Finally, since the marketplace is a competitive arena, it must also consider economics at all times. Because diet formulation is quite complex when carried out properly, computers are used to reduce demands on time and avoid calculation errors, and to provide flexibility. Manual methods can still be used, but they are very limiting in scope and capability.

Topic 7: Formulating diets – introduction

With the ingredients selected and evaluated, the next step is to put the information into a formula that will calculate the required diet. This can be done using manual calculation, spreadsheet programs or least–cost formulation computer software packages. Diet formulation is not a simple matter and is best left to qualified nutritionists. Essentially, it is a process that matches the nutrient requirements of the animal with the nutrients present in available ingredients. It must consider not only the many individual nutritional components, such as energy, amino acids, minerals and vitamins, but also ensure that important ratios, such as energy:amino acids and calcium:phosphorus are maintained within an acceptable range. The process should provide safety margins that avoid unwanted surprises, while at the same time avoiding costly over–formulation. Finally, since the marketplace is a competitive arena, it must also consider economics at all times. Because diet formulation is quite complex when carried out properly, computers are used to reduce demands on time and avoid calculation errors, and to provide flexibility. Manual methods can still be used, but they are very limiting in scope and capability.

Topic 8: Assessing the Nutritive Value of Feeds – Physical Characteristics

Strictly speaking, the term nutritive value probably should not be used unless the value is obtained by offering the feeds to the relevant type and class of animal for which the feed is intended. Inefficiency in the capture and absorption of nutrients varies with the animals and the conditions in which a feed is being used. The first major loss is undigested nutrients excreted in the faeces (and also smaller losses of energy as methane produced in the gut). When a nutrient is determined quantitatively in the feed and the faeces, the apparent digestibility of that ingredient can be calculated.

Topic 9: Assessing the Nutritive Value of Feeds – Bioassay

On completion of this topic you should have:

  • An appreciation of the background to the current focus on sustainability in Australia and elsewhere;
  • An understanding of the determinants of world wool market trends and how they impact on the economics of wool growing;
  • An understanding of the key economic principles associated with sustainability; and
  • An introduction to how government can promote sustainability

Topic 10: Predicting Nutrient Digestibilities

The concept that the nutritive value of feeds is predicted from their chemical composition is highly attractive because bioassays are tedious and expensive. Numerous prediction equations have been and are continuously being published, but none has been accepted universally. This is, however, not to say that all the equations are invalid. For example, the equation for estimation of dry matter digestibility is well accepted for predicting digestibility in roughage–fed ruminants. In pigs and poultry, dietary non–starch polysaccharide (bulk of the fibre component) levels are negatively correlated with nutrient digestibilities and an in vitro method based on this relationship is of great interest to the feed and livestock industries throughout the world.

Topic 11: Nutritive Values of Individual Ingredients

Feedstuffs are divided into three major types: energy sources, protein sources and mineral sources. They can all come from both plants and animals. Energy is obtained from grains and oils and tallow. Protein concentrates include soybean meal and meatmeal and amino acid imbalance can be ameliorated by the inclusion of synthetic amino acids. Minerals such as calcium can be obtained directly from mineral sources such as limestone and oyster shell.

Topic 12: Understanding Nutrient Requirements and Diet Formulation

The objective in formulating diets is to provide animals with a consumable quantity of feed stuffs that will supply all required nutrients in adequate or greater amounts and to do so in a cost effective way. Today, almost all diets are formulated with the aid of computer software. Use of computers has resulted in more complete evaluations of nutrient profiles in diets and allowed for economics to be included in diet formulation decisions.

Topic 13: Practical Considerations when Manufacturing and Selecting Feeds

The operation of a feed mill or a farm is dictated by the types of ingredients available and their current prices. These ingredients are not necessarily the most nutritious ones or the most appropriate ones for the type of production system the farmer has. So the knowledge of the ingredients in terms of factors causing variation in chemical composition and nutritive value, and strategies minimising their effects is of paramount importance in diet formulation.


MODULE 3: Grain Feeding

On completion of this topic you should be able to:

  • Discuss the animal factors influencing starch digestion in ruminants.
  • Discuss the dietary factors influencing starch digestion in ruminants.
  • Describe the biochemical processes of starch digestion and the importance of volatile fatty acid production to this process.

Ruminant animals have evolved with the unique capacity to digest cellulose. The digestive tract of ruminants has developed in a way that allows them to survive and produce on roughage-based diets. In recent years, there has been an increasing incentive to feed concentrate diets based on cereal grains. The feeding of grain-based diets can improve animal production and produce a meat product that is more desirable to the consumer.

As ruminants have evolved to consume roughage-based diets, the provision of grain-based diets can cause digestive problems that may lead to morbidity and mortality. Therefore, careful management of grain-based feeding to ruminants is required. With careful management, significant improvements in the quality and quantity of production (milk, wool, meat and reproduction) can be achieved.

This module will provide you with an understanding of the metabolic implications associated with introducing grain-based diets to ruminant production systems and therefore an understanding of the management strategies available for commercial production.

Topic 14: Digestion of Grain

Ruminant animals have evolved with the unique capacity to digest cellulose. The digestive tract of ruminants has developed in a way that allows them to survive and produce on roughage-based diets. In recent years, there has been an increasing incentive to feed concentrate diets based on cereal grains. The feeding of grain-based diets can improve animal production and produce a meat product that is more desirable to the consumer.

Topic 15: Characteristics of Grain that Influence Starch Digestion

The selection of a grain and method of processing should aim to provide a feed that suits the digestive capacity of the animal. Differences between grains are based not only on the macro nutrients such as starch, lipid and protein, but also on components such as non–starch polysaccharides (NSP), which can have a negative effect on intestinal digestion, and lignin which reduces fermentative digestion. The characteristics of starch granules and the endosperm matrix also have important effects on digestibility and response to processing, and must be considered when designing processing techniques.

Topic 16: Methods of Processing Grain

This topic coverd three major subjects. Firstly there is a description of each type of grain processing. Secondly there is a discussion of the way grain processing can change site of digestion and thirdly, there is discussion of the objectives of grain processing.

Topic 17: Grain Storage, Exogenous Enzymes and Germination

The storage of grain is a most important component of any grain feeding production system. Inappropriately managed storage systems can reduce grain quality and even render grain unsuitable for feeding to livestock. For opportunistic grain feeding production systems, grain storage can provide significant financial benefits by allowing the producer to purchase grains at times when demand and therefore prices ($/tonne) are lower than during the peak demand periods. It is not unusually for grain prices to fluctuate by more than 100% between the high and low demand periods. This topic will introduce you to some of the common problems encountered with grain storage and management options available for addressing and preventing these problems.

Topic 18: Chemical and physical treatment of roughages to improve digestibility

The feeding of ruminant livestock in many countries of the world is dependent on readily available low quality roughages or crop residues. In poorer countries that are densely populated, opportunities for supplementing these animals with products such as cereal grain, urea or molasses are limited. In addition, production systems in these countries are typically small but intensive, with one family often owning only a few head of livestock. In such situations, cattle may provide milk for the family, or draft to prepare the soil for planting and reproduction to produce replacement animals. Poor quality roughages such as rice straw have low digestibility and only move slowly through the rumen. As a result intake is also low and digestible energy intake (feed intake multiplied by digestibility) is also low, so production is limited. Strategies aimed at improving the quality of low quality roughages are therefore needed. This topic will introduce you to several examples of chemical and physical treatments of roughages that can considerably improve their nutritive value for livestock. Despite the potential value of treatments, adoption has been relatively low.

Topic 19: Hormonal Growth Promotants and Nutritional Requirements

Although hormonal growth promoters (HPGs) are not strictly nutritional inputs their use in animals alters animals’ nutrient requirements: it is important to understand how to manage the diet of animals treated with these compounds. There are a number of agents that can have a profound effect on nutrient utilisation and tissue metabolism. In this lecture, we will consider these agents under three categories: hormones related to the sex steroids that are all used for ruminant production; growth hormone and its use in dairy cattle and pig production; beta agonists and other tissue growth factors.

Topic 20: Growth Promotants for Pigs and Poultry

Animal production in the last 50 years has become much more intensive. Intensification has imposed a need to maintain consistently high production rates and a greater degree of disease control. This quest for increased animal performance and health status has resulted in reliance on application of low doses of antibiotics in feeds. Between 1950 and 1970, most classes of antibiotics were used as growth promotants, primarily in pigs and poultry, at inclusion rates in diets of about 50 ppm. Responses in production were consistently of the order of 10 to 15 %, and improvements in feed conversion averaged 5%, although the level of response has depended on environmental factors and, of course, pathogen loads present. Consistent growth responses to these antibiotics have been maintained over the years, and have provided livestock managers with a reliable tool to maintain good production levels.

Topic 21: Acidosis and its Control in Ruminants

Acidosis is a digestive condition that can result from the feeding of grain sources to ruminant animals. Acidosis can be fatal and if not fatal, can result in long-term reductions in productivity. Acidosis is considered one of the major health and welfare issues facing the intensive feeding sectors of the Australian sheep and cattle industries. Acidosis can be managed. This topic will cover many of the strategies used for managing acidosis and you will be introduced to the metabolic conditions that result in acidotic events. With a greater understanding of the mechanisms by which acidosis can occur you will be better equipped to apply strategies for managing acidosis.


MODULE 4: Nutrition management for grazing animals

On completion of this topic you should be able to:

  • Discuss the importance of efficient microbial activity on the digestion of nutrients.
  • Discuss the importance of the provision of carbohydrate and ammonia to rumen bacteria.
  • Describe how changes in diets of ruminants can alter volatile fatty acid production and the impact of these changes on energy availability to the animal.
  • Describe the ideal rumen conditions for maximising microbial protein production

Feeding ruminant animals is often described in industry as feeding two animals – feeding the livestock (sheep or cattle) and feeding the “rumen bugs”. While this concept has some merit, it is hoped that by the end of this topic you will understand that as animal managers we are in fact feeding millions of animal and plants that make up the “rumen microflora and fauna”. This is important to understand as the balance of the rumen bacteria, protozoa and fungi will change with diet composition and this can influence the effectiveness of the feeding strategy.

The rumen bacteria have a particular requirement for ammonia, which allows the production of microbial protein. This is a unique ability of ruminants, allowing the feeding of non-protein nitrogen sources (such as urea) that will enable the production of protein. In this topic you will cover the process of digestion by the rumen bacteria and the important roles that fungi and protozoa play. The mechanisms of microbial protein production and the factors influencing the efficiency of this process will also be introduced.

 Topic 22: Rumen Function and Protein Supply to the Host Animal

Feeding ruminant animals is often described in industry as feeding two animals – feeding the livestock (sheep or cattle) and feeding the “rumen bugs”. While this concept has some merit, it is hoped that by the end of this topic you will understand that as animal managers we are in fact feeding billions of tiny plants and animals that make up the “rumen microflora and fauna”. It’s important to understand this, as the balance of rumen bacteria, protozoa and fungi changes with diet composition and this can influence the effectiveness of the feeding strategy.

Topic 23: Factors Influencing the Voluntary Intake of Food

The productivity of animals is determined mainly by the amount of food they eat and, although there are times when intake is deliberately restricted so as to merely maintain animals or to eke out sparse resources, the usual aim of management is to allow the animal to achieve the maximum intake for the particular feeding situation. This level is known as the animal’s voluntary intake of the feed and is measured in kg of dry matter per day (kg DM/d) because of the wide variation in feed DM%, e.g. from <15% to >60% in herbage. For hand-fed animals in feedlots or dairies, the main reason for wanting to know their voluntary intake is to ensure that a weighed ration of a formulated diet is within the animal’s capacity. Most other ruminants in Australia subsist almost entirely on grazed pasture and here the situation is quite different.

Topic 24: Diet Selection

In natural environments, grazing animals do not simply work their way through the pasture in front of them devouring everything in sight! They eat some plants and leave others, and they even choose certain plant parts (e.g. leaves) and leave others (e.g. stems). The situation with intensively managed animals is more subtle, but examination of what animals ingest from a food bin, and of what they leave uneaten, reveals that they too are selective in what they choose to eat.

Topic 25: Principles of Supplementary Feeding in Grazing Systems

In many grazing systems, there are times of the year when animals will require supplementation because the nutrient supply from grazing does not meet their demands for nutrients. Feed supplements used in the various grazing industries include not only feed purchased off-farm, but also feed grown on-farm (e.g., wheat) or formulated on-farm from a mixture of grown and purchased commodities. In grazing enterprises, the cost of supplementary feeding is one of the major discretionary expenditures faced by farmers and, equally importantly, is also a major contributor to the so-called ‘down-side risk’ in farm income. This is the increased year-to-year variability in farm income generated by the costs of extra supplementary feeding in bad seasons which, because stocking rates are frequently suboptimal, is often not compensated for by the extra income generated in good years. Increases in the efficiency of supplementary feeding are of thus economic importance and will have a major effect on farm income.

Topic 26: Supplementary Feeding for Wool Growth and Reproduction

In many grazing systems, there are times of the year when animals will require supplementation because the nutrient supply from grazing does not meet their demands for nutrients. Feed supplements used in the various grazing industries include not only feed purchased off-farm, but also feed grown on-farm (e.g., wheat) or formulated on-farm from a mixture of grown and purchased commodities. In grazing enterprises, the cost of supplementary feeding is one of the major discretionary expenditures faced by farmers and, equally importantly, is also a major contributor to the so-called ‘down-side risk’ in farm income. This is the increased year-to-year variability in farm income generated by the costs of extra supplementary feeding in bad seasons which, because stocking rates are frequently suboptimal, is often not compensated for by the extra income generated in good years. Increases in the efficiency of supplementary feeding are of thus economic importance and will have a major effect on farm income.

Topic 27: Supplementation of Ruminants – Dry Pasture

Supplementary feeding of livestock is a wide-spread practice in Australia. Supplementary feeding may be undertaken in drought conditions, for the purpose of survival or for production purposes. Most of Australia’s livestock production systems rely on native pasture in regions of low rainfall and low humidity. In many situations, the quality of pasture available to animals is more limiting than the quantity of pasture available. Therefore, supplementation practices are frequently designed to enable greater nutritive value to be extracted from the available feed. This topic covers some of the common supplementation practices used in Australia and describes the nutritional principles underpinning these practices.

Topic 28: Ketosis and Urea Poisoning

Pregnancy toxaemia is a relatively common metabolic disorder in Australian sheep production systems. Unfortunately, this type of metabolic disorder is not limited to sheep production but also beef cattle, dairy cattle, pigs and poultry. This topic describes the metabolic processes that lead to the development of ketosis and pregnancy toxaemia and strategies available for the prevention and management. Due to Australia’s reliance on low quality native pastures for its livestock production, urea is a widely used supplement. While urea can be a relatively cheap and effective supplement for ruminant animals, it can also be fatally toxic. The processes by which urea toxicity can occur in ruminants and recommendations for the use of urea that will minimise the risk of toxicity are described.

Topic 29: Precision Nutrition for Grazing Sheep

Precision nutrition of grazing animals is a very new field of animal nutrition that is made possible by the convergence of a number of new technologies. Automatic walk-over weighing allows monitoring of individual animals, electronic (Radio Frequency) identification allows individual animals to be monitored and managed and wireless data transfer allows sophisticated use of information, even in remote locations. The concept of feeding an animal to meet its requirements and production potential is not new. Individual animal feeding is very common in the dairy industry where the level of milk production and the cows’ stage of lactation determine the amount of concentrate fed to each cow. Until the availability of new management technologies developed by the Sheep CRC, this level of sophistication has not been available for the management of grazing animals.


MODULE 5: Companion Animal Nutrition

On completion of this module you should:

  • Understand the concepts of feeding companion animals based on their nutrient and energy requirements
  • Understand the nutritional needs of dogs and cats in relation to their phylogeny and ancestral origins
  • Be able to apply appropriate feeding strategies for dogs and cats in different life stages and physiological states
  • Have a basic knowledge of the dietary factors that impact on companion animal health and some dietary strategies for disease prevention
  • Understand the nutritional claims of pet foods and how these are substantiated

The first commercial dog food was produced and sold in London in 1860 by James Spratt and by the mid 1930’s there were several brands available on the supermarket shelves. By 1992 commercially prepared dog foods accounted for more than 60 percent of all food fed to dogs in Australia. This century has seen an increased awareness of the nutritional needs of dogs and cats, with an increased focus on animal health. The ready availability of nutritionally complete and balanced commercial pet foods has greatly reduced the incidence of nutritional deficiencies. Dogs and cats of today are more likely to suffer nutritional imbalances related to over-consumption and over-supplementation than deficiencies due to nutritionally inadequate diets.

Topic 30: Nutrient requirements of dogs and cats

The basic nutrient requirements of dogs and cats is similar to those of all animals; energy, protein, vitamins, minerals and water.  However, companion animals, and in particular cats, have a unique suite of requirements outside those previously discussed in this text.  Also, the objective of companion animal nutrition is to maintain a healthy pet for many years, unlike many other domestic animal species.

Water and energy requirements are discussed in this topic with specific reference to the differences between cats and dogs.

Topic 31: Feeding throughout the life cycle

With respect to companion animals this topic covers:

  • Feeding management
  • Pregnancy and lactation
  • Growth
  • Geriatric nutrition

Topic 32: Diet related health disorders in dogs and cats

With respect to companion animals this topic covers:

  • Obesity Diabetes
  • Mellitus Periodontal disease
  • Inherited metabolic disorders
  • Vitamin deficiencies and excesses

Amongst the array of health problems afflicting our canine and feline companions, there are those that can be classified as diet-related, being either directly attributable to the diet; or the condition being ameliorated by dietary intervention even where the diet is not the cause of the disease (e.g. some inherited metabolic disorders). This topic covers some of the more common diet-related health disorders in dogs and cats.