Equine Science

Zoe Davies

• Éditeur: Wiley-Blackwell
• Année: 2017
• ISBN:
  9781118741160
• Édition: 3
• Sujet: Medicine
• Sous-sujet: Equine Veterinary Science

From genetics to functional anatomy, cell biology to the equine digestive system, Equine Science, Third Edition covers all the essential scientific knowledge you need for your equine programme. Thoroughly updated, this new edition features a clear, systematic presentation, stunning full-colour photographs and illustrations, chapter summary points and self-assessment questions throughout.

• Describes the structure and function of the various body systems of the horse
• Explains the scientific rationale behind modern equine training practices
• Features new chapters on exercise physiology and the evolution of the horse
• Reflects the latest scientific advances and changes in the student curriculum
• Includes new information on circadian rhythms and sleep patterns, the immune system, and hindgut microbiology.

A powerful teaching and learning aid, Equine Science, Third Edition is an essential text for students on higher education equine studies and equine science programmes, as well as those studying for BHS qualifications up to BHSII Stage 4 Horse Knowledge and Care.

Chapter 1
The Biochemical Nature of Cells

Biochemistry is the study of chemicals within biology. A knowledge of biological molecules and their structure and function is essential for a full understanding of the nature, performance and behaviour of horses. There are approximately one hundred elements that exist on Earth; of these, 16 are essential for life and only four make up 95% of all living matter, namely carbon, hydrogen, oxygen and nitrogen.

The combination of carbon with other elements creates a huge variety of organic molecules, and all organic compounds therefore contain a carbon backbone. The four main classes of organic molecules are proteins, carbohydrates, lipids and nucleic acids. In addition, a relatively small number of inorganic ions such as sodium and potassium are essential for life, as components of larger molecules or extracellular fluids. Table 1.1 shows examples of organic and inorganic molecules.

Table 1.1 Examples of organic and inorganic compounds in the horse's body

Organic compounds	Inorganic compounds
Glucose (C6H12O6)	Water (H2O)
Ethane (C2H6)	Ammonia (NH3)
Glycine (amino acid) (C2H5NO2)	Carbon dioxide (CO2)
Cytosine (nucleotide base) (C4H5N3O)	Nitrate ion (NO3–)

Horses therefore contain water plus a huge number of macromolecules which have been built up from smaller simpler ones. These molecules are also involved in the basic structure and function of all cells (Figure 1.1). These simple building blocks are similar in all organisms, suggesting a common origin for all life forms.

Figure 1.1 The biochemical nature of cells.

Metabolism

All chemical reactions that take place within the horse are collectively known as ‘metabolism’. Metabolic reactions can be anabolic (building up large molecules from smaller ones) or catabolic (breaking down larger molecules into smaller ones). Anabolic reactions usually involve removal of water molecules and are known as condensation reactions, such as when glycogen is built up from glucose molecules. Catabolic reactions are the reverse and usually involve larger molecules being split when reacting with water. These are known as hydrolysis reactions, for example digestion of proteins in the digestive system.

Horses must have a supply of energy to fuel energy-requiring processes, such as sustaining life and movement. This is obtained from cellular respiration – the oxidation of organic molecules such as glucose into simpler molecules namely carbon dioxide and water.

Water

All life on Earth began in water and water is the main component of all organisms, including horses, providing an environment in which metabolic reactions can occur. Approximately 65–70% of the bodyweight (bwt) of the horse on a fat-free basis is made up of water and newborn foals may contain as much as 90% water. Male horses contain slightly more water than females.

Fluids are present in the body in two main compartments: inside cells and outside cells. Approximately two-thirds of water is found within cells and this is known as intracellular fluid (ICF). The remainder (one-third) is outside cells and is called extracellular fluid (ECF). From this, roughly 80% of ECF is found in interstitial fluid, that is, bathing and surrounding cells in tissues, and about 20% in blood plasma. Interstitial fluid encompasses lymph, cerebrospinal fluid, synovial fluid, and pleural, pericardial and peritoneal fluids, to name but a few.

The horse's body also naturally generates metabolic water as a result of breaking down protein, carbohydrates and fat, mostly from condensation reactions. This does not provide a large amount of water, but does contribute to the daily water balance and may change the horse's need for water. Diet will also affect water requirements. Horses grazing on pasture which has a low dry matter will sometimes drink little or no additional water compared to those on a mostly dry forage diet such as hay. Voluntary water intake by resting horses in a moderate temperature environment is roughly 25–70 ml/kg bwt/day. For a 500-kg horse ...