Fundamentals of Applied Animal Nutrition

Gordon Dryden

• Éditeur: CAB International
• Année: 2021
• ISBN:
  9781786394477
• Sujet: Technologie et ingénierie
• Sous-sujet: Élevage d'animaux

If you have ever wondered why animals prefer some foods and not others, how poor feeding management can cause conditions such as laminitis, rumenitis or diarrhoea, or how to construct a diet to optimise animal performance and health, then this book will introduce you to the fundamentals of animal nutrition and their practical implementation.While giving a comprehensive and practical overview of the principles that underpin the design and management of farm animal feeding systems, this book: - Covers a wide range of topics from digestive function, nutrients and feed composition, to intake, feed related disorders, grazing behaviour and management, as well as how animals influence climate change and the environment.- Contains hints, tips and practical advice on animal feeding.- Includes links to the latest data on feed composition and nutrient requirements.- Is a companion book to the author's book titled Animal Nutrition Science.With its evidence-based approach and emphasis on the practical throughout, this is a valuable textbook for undergraduate and graduate animal science students studying the feeding of farm animals. It is also an essential reference for early practitioners, veterinarians, farm managers and advisers in animal feed companies.

1 Nutrients and important feed constituents and their functions

Introduction

Almost the first thing that we think about when we have animals to care for or manage is ‘How should I feed them?’ And the answer to that question starts with answering two other questions: ‘Why do animals need feed?’ and ‘What actually is feed?’ These topics are discussed in this chapter.

Terms used to describe animal feed:

• ‘Food’ is a term which is often reserved for human foodstuffs, while animal feed is usually called ‘feed’. This usage is arbitrary and either word can be used to refer to animal feed.

• ‘Ingredient’ is a term used to describe individual feeds and is often used to refer to the components of rations. ‘Feedstuff’ has a similar meaning.

• ‘Diet’ and ‘ration’ often have the same meaning in animal nutrition. The term ‘ration’ is usually reserved for a mixture of feed ingredients which has been formulated to provide specific amounts of nutrients. ‘Diet’ usually means the same as ‘ration’, or even ‘feed’, but it can also imply a particular type and/or amount of feed or mixture of ingredients.

• ‘Concentrates’ are feeds which have little fibre and usually a fairly high level of starch and/or protein (Chapter 6). They are plant seeds and fruits, and by-products made from these, and feeds made from animal tissues and products.

• ‘Roughages’ are feeds which contain relatively high levels of fibre (Chapter 6). They are often forages, i.e. the vegetative parts of pasture plants. ‘Roughage’ is used in human nutrition to mean indigestible fibre, but this is an incorrect usage in animal nutrition.

Why do animals need feed?

There are five reasons why animals need feed:

• If an animal is growing or otherwise producing, it needs external sources of the components of body tissue (for growth), and of its products (such as eggs, milk, etc.).

• Body cell components and metabolites are continually synthesized and broken down. Many of these constituents are synthesized from recycled precursors, but there is some inevitable wastage. This has to be made up by materials obtained from feed.

• Animals need energy to fuel the biochemical reactions and physiological processes which keep them alive, healthy and productive.

• Animal cells use a wide variety of chemical substances in their metabolism. Most of these are made by the animal itself but there is a range of compounds which animals cannot make. These include minerals, most vitamins, and some amino acids and fatty acids. These must be supplied from external sources, i.e. the animal’s feed.

• Some feed constituents promote wellbeing, e.g. fibre supports digestive tract function and health, tannins help to control intestinal parasites, some minerals have pharmacological effects, and ruminally degradable protein (RDP) is essential for rumen micro-organisms.

The chemical composition of feeds

Feed analysis begins with measuring the feed’s water and dry matter (DM) contents. Within the DM we have the organic matter (OM) and minerals; and the OM can be further divided into fibre, non-fibrous (non-structural) carbohydrates, protein, fat, vitamins and non-nutrient substances.

The analytical methods used to determine these fractions are briefly described in Table 1.1. The basic method used is the proximate analysis (developed in the latter part of the 19th century) which identifies DM, crude protein, crude fibre, crude fat (ether extract) and crude minerals (ash). The proximate analysis is now supported by newer methods, including detergent extraction for measuring fibre, atomic absorption spectroscopy for the individual minerals and chromatography for measuring fatty acids, amino acids and vitamins. These methods are fully described in Nielsen (2017) and AOAC (2019).

Table 1.1. Methods of measuring the nutritionally important constituents of feeds.

Food constituent	Analytical method
Dry matter (DM)	Measured by heating the feed, usually at 100°C for several hours; fresh forages may be dried at 50–60°C to avoid heat damage to proteins and loss of carbohydrates and other constituents
Organic matter (OM)	Determined as the loss of mass after ashing (see below)
Fibre (acid detergent fibre, ADF; neutral detergent fibre, NDF; and crude fibre, CF)	ADF and NDF are the residues which are resistant to the actions of either acid detergent (cetyltrimethylammonium bromide in sulphuric acid) or neutral detergent (sodium dodecyl sulphate in a pH 7 solution). Early methods of fibre analysis used a sequential extraction with acid and alkali to give a residue called CF. This analysis is now not often used and has been replaced with the more reliable detergent methods
Protein (crude) (CP or Prot.)	Determined by measuring the total N content (using the Kjeldahl or Dumas methods) and multiplying this by 6.25. This method assumes that all the feed N is from protein, and that all proteins contain 16% N. Neither of these assumptions is completely correct, so CP values often overestimate the actual protein content. The individual amino acids which make up proteins are measured by chromatography
Non-structural carbohydrates (NSC) or water-soluble carbohydrate (WSC)	These are carbohydrates which are not part of the plant cell wall. NSC includes starch and WSC. WSC is simple sugars (see text), β-glucans and fructans. These compounds are measured by polarimetry, ethanol extraction, and enzymatic methods
Fat (crude) (EE, for ‘ether extract’)	Diethyl ether, petroleum ether, or hexane are used to extract fats and other substances such as phospholipids, waxes, fat-soluble vitamins, and pigments. This constituent is also called ‘ether extract’. Individual fatty acids are measured by chromatography
Minerals (ash)	Ash is measured by burning a sample at 500°C or more for several hours. The ash contains most of the minerals – although some are lost by volatilization; this analysis is now more used for determining the organic matter content (see text). Data on individu...