Equine Medicine, Surgery and Reproduction - E-Book

Tim Mair, Sandy Love, James Schumacher, Roger K. W. Smith, Grant Frazer

• Publisher: Saunders Ltd.
• Year: 2013
• ISBN:
  9780702052026
• Edition: 2
• Topic: Medicine
• Subtopic: Equine Veterinary Science

The new edition of this introductory-level textbook continues to offer a concise and approachable bridge between student lecture notes and more detailed clinical reference works. All aspects of equine medicine, surgery and reproduction are covered in a single, convenient volume. The second edition has been subject to an extensive revision, with each chapter updated and new chapters added to cover wound management, critical care, anaesthesia and sedation, and diagnostic imaging. While offering key information in an easily and quickly digested format for clinical veterinary students and practising veterinary surgeons, this second edition of Equine Medicine, Surgery and Reproduction will also be relevant to students undertaking equine science degrees, and to professional horse owners and trainers.

The wide range of international contributors, highly experienced and all experts in their fields, ensures that the new edition of this popular all-in-one resource remains as indispensable as ever.

• Comprehensive coverage of all areas of equine medicine, surgery and reproduction
• Easy-to-use format
• Completely revised since the first edition with new chapters added
• Now with over 100 new illustrations including colour photographs
• Includes diagnostic and therapeutic information as well as descriptions of commonly employed clinical techniques
• Includes lists of important differential diagnoses for common clinical signs

Chapter 1

Upper alimentary system

J. Geoffrey Lane and Robert Pascoe

Contents

1.1 Normal upper alimentary tract function: deglutition

Oral, pharyngeal and oesophageal phases of deglutition

Prehension

Mastication

Lingual function

Elevation of palate

Pharyngeal constriction

Laryngeal protection

Crico-pharyngeal relaxation

Primary and secondary oesophageal peristalsis

1.2 Diagnostic approach to cases of dysphagia

History – signs of dysphagia

Physical examination, external and oral inspection

Endoscopy per nasum

Radiography and fluoroscopy

Oral examination under general anaesthesia

1.3 Aetiology of dysphagia: oral phase abnormalities

Facial palsy and lip lesions

Temporo-mandibular joint and hyoid disorders

Lingual abnormalities

Dental disorders

Congenital and acquired palatal defects

Other oral conditions: foreign bodies, neoplasia

1.4 Aetiology of dysphagia: pharyngeal phase abnormalities

Pharyngeal paralysis

Pharyngeal compression: strangles abscessation

Pharyngeal cysts, palatal cysts

Epiglottal lesions, including sub-epiglottic cysts

Laryngeal abnormalities

Fourth branchial arch defects (4-BAD)

1.5 Aetiology of dysphagia: oesophageal phase abnormalities

Megaoesophagus

Oesophageal obstruction (‘choke’)

Oesophageal strictures/stenosis

Intra-mural oesophageal cysts

Oesophageal rupture

Neoplasia

‘Wind-sucking’

Grass sickness

1.6 Oral trauma, mandibular fractures etc.

1.7 Oesophageal obstruction

1.8 Anatomy of the oral cavity

Oral cavity

Normal dental anatomy

Triadan system

Eruption of teeth

1.9 Abnormalities of wear – abrasion and attrition

1.10 Periodontal disease

1.11 Dental caries

1.12 Endodontic disease including dental abscessation

1.13 Tumours of the upper alimentary tract

Odontogenic tumours

Other tumours of the jaw

1.14 Diagnostic approach to dental disorders

Ageing of horses by dentition

Clinical signs of dental disease

Oral examination

Radiography of teeth

Other ancillary diagnostic techniques

Indications for dental extraction

Options for the extraction of incisors, canines and wolf teeth

Options for the extraction of cheek teeth

Further reading

1.1 Normal upper alimentary tract function: deglutition

Normal deglutition comprises the prehension and mastication of ingesta followed by its transfer from the oro-pharynx to the stomach.

Oral, pharyngeal and oesophageal phases of deglutition

Deglutition is divided into three stages:

1. The oral phase – which includes the gathering of food, movements within the oral cavity, mastication and the formation of boluses of ingesta at the base of the tongue – is under voluntary control.

2. The presence of a bolus gathered at the tongue base triggers the sequence of reflexes, collectively known as swallowing, which propels the ingesta from the pharynx – the pharyngeal phase – into the oesophagus. The glosso-pharyngeal nerve (IX) and the pharyngeal branches of the vagus (X) innervate the pharynx and larynx, and their afferent and efferent pathways are co-ordinated in the swallowing centre in the brainstem.

3. Waves of peristalsis convey the ingesta along the oesophagus to the stomach – the oesophageal phase of deglutition.

Prehension

Prehension in the horse relies on the incisor teeth to grasp and section herbage and on the lips to pick up smaller pieces of ingesta as well as to contain it within the mouth and to manipulate food towards the cheek teeth.

Mastication

The molar and premolar teeth are responsible for the mechanical crushing of the fibrous diet.

The tongue and buccal musculature assist in manipulating the ingesta between the maxillary and mandibular dental arcades.

Mastication requires free opening and closure of the temporo-mandibular joints (TMJs) through the action of the masticatory muscles – the masseter, pterygoid and temporal muscles close the jaws, and gravity, assisted by the digastric muscles, opens them. The masticatory muscles receive their innervation through the mandibular branch of the trigeminal nerve (V).

The shape of the articular surfaces of the TMJs together with the presence of menisci permit lateral movements by the mandibular teeth across the wearing surfaces of the upper cheek teeth.

Lingual function

The tip of the tongue assists in prehension and moves the ingesta between the cheek teeth.

Contraction of the tongue base helps in the formation of boluses and, once collected, each bolus is driven caudally; this triggers the involuntary phases of deglutition by driving food and fluid caudally from the oro-pharynx.

The tongue is attached to the hyoid apparatus, and free movement at the tympano-hyoid articulation is required for the craniocaudal tongue motion which facilitates bolus formation in the oro-pharynx.

The glossal musculature receives its motor supply via the hypoglossal nerve (XII).

Elevation of palate

The action of the levator palatini muscles draws the soft palate dorsally to close off the naso-pharynx and prevents the nasal reflux of ingesta; this marks the onset of the involuntary stages of deglutition.

The horse has an intra-narial larynx at all times other than during the momentary disengagement for deglutition. (See 5.18 and 5.21.)

The levator palatini muscles lie parallel with the drainage ostia of the auditory tube diverticula (ATDs) so that when they contract the ostia open to allow exchanges of air for pressure equilibration across the ear drum.

Pharyngeal constriction

The constrictor action of the circular muscles of the pharyngeal walls embraces both oro-pharynx and naso-pharynx – the latter can be appreciated during endoscopic examinations of the naso-pharynx. A wave of constriction follows the contraction of the tongue base and passes from rostral to caudal efficiently to empty the oro-pharynx – the pharyngeal ‘stripping’ wave – leaving minimal quantities of ingesta at the base of the tongue.

Laryngeal protection

Aspiration of food and fluid through the rima glottidis is prevented primarily by the tight adduction of the vocal folds and arytenoid cartilages and to a lesser extent by the retroversion of the apex of the epiglottis.

Crico-pharyngeal relaxation

The upper oesophageal sphincter is formed by the thyro- and crico-pharyngeus muscles, and these are maintained in a state of contraction to prevent involuntary aerophagia, especially during forced exercise. Relaxation of the crico-pharynx simultaneous with the pharyngeal stripping wave permits the food and fluid boluses to pass caudally into the proximal oesophagus.

Primary and secondary oesophageal peristalsis

After each bolus has passed through into the proximal oesophagus, primary peristaltic waves are initiated by active closure of the cricopharynx.

Primary oesophageal peristalsis carries individual boluses to the cardia, but the process is not completely efficient and small quantities of ingesta are left at variable levels in both the cervical and thoracic oesophagus, even in normal horses. These ingesta are either picked up in the bolus of a subsequent primary wave or by locally generated secondary peristalsis.

1.2 Diagnostic approach to cases of dysphagia

History – signs of dysphagia

The signs of dysphagia include:

• an unwillingness to eat.

• slow, messy feeding.

• halitosis.

• rejection of semi-masticated food onto the ground (quidding).

• productive coughing.

• nasal reflux of saliva, ingesta and fluids.

Obviously, horses that are unable to eat and swallow food are likely to lose weight rapidly, but this process is accelerated if the horse develops secondary inhalation pneumonia, which is a common sequel to dysphagia. A moist cough is typical of animals aspirating food or saliva into the rima glottidis. In addition to a clear case history, careful observation of the patient's attempts to eat and drink should be made.

If the horse shows return of ingesta from its mouth, the site of the lesion causing the dysfunction must lie in the oral cavity or oropharynx.

Nasal reflux of ingesta points to an abnormality of the pharyngeal or oesophageal phase of deglutition (Figure 1.1).

Figure 1.1 Nasal reflux of saliva and ingesta in a case of acute oesophageal obstruction.

Physical examination, external and oral inspection

Evidence of systemic and/or toxic disease, including Streptococcus equi infection, botulism, grass sickness, rabies, upper motor neur...