The Equine Digestive Tract

Transcription

1 The Equine Digestive Tract Week 1 Lecture 2 Clair Thunes, PhD Animal Science 126 Equine Nutrition Teeth Horses are born with no visible teeth but have 24 deciduous teeth (temporary or milk teeth) and either 40 (female) or 44 (males)permanent teeth. Horses have 4 types of teeth; Incisors which cut Premolars and molars which grind feed Canine teeth typically only in males which accounts for the 4 extra teeth Teeth 1

2 The incisors are used to nip and tear food and also in defense. The horse is born with no visible incisors but the central incisors appear soon after birth < 2 weeks. The laterals at 4-6 weeks and the corner incisors at 6-9 months. These deciduous teeth are replaced at 2.5yrs for the central incisors, 3.5 yrs for the laterals, and 4.5yrs for the corners. The angle made by the maxillary and mandibular incisors is approx. 180 degrees in young horses decreasing to 90 degrees by 15 years. Saliva Purpose to moisten and soften food for passage 3 pairs of glands, parotid most active Average daily production 12 liters (3 gallons) Only produced when chewing High concentration of calcium and bicarbonate Slaframine in clover (caused by fungus) can lead to excessive salivation. Generally in spring and summer. Digestive Tract Stomach S.I. Cecum Large Colon Small Colon Fore Gut 38.5% Hind Gut 61.5% 2

3 The Stomach equinegastriculcers.co.uk Stomach After food leaves the mouth and travels down esophagus reaches the stomach Stomach essentially two parts an upper 1/3 and lower 2/3rds Each covered in different types of cells Upper portion is covered in Squamous cells Lower portion Glandular cells Stomach in an 1100lb horse stomach holds 2 to 4 gallons 75% ingested liquids pass stomach within 30mins 25% of feed dry matter in 30mins, 98% in 12hrs hydrochloric acid from parietal cells - lowers ph denaturing dietary proteins - activates pepsin pepsin - hydrolyses/breaks peptide bonds in proteins 3

4 Stomach Cont. Gastric acid constantly secreted into glandular portion Cells protected by mucin ulcers occur here when mucin compromised For example due to medications Squamous cells not protected by mucin contact with acid causes ulceration. Many ulcers occur around oesophagus The Stomach equinegastriculcers.co.uk Stomach Cardiac region a thin strip adjacent to the margo plicatus little is known about secretory products, it is the site of ulceration in neonatal foals under stress. Fundic mucosa contains parietal cells which secrete acid, Zymogen cells which secrete pepsin and lipase, and enterochromaffin-like (ECL) cells that secrete histamine in response to gastrin. The pyloric mucosal region is the site of G-cells which synthesize gastrin. D-cells, produce somatostatin that suppresses gastrin release from Gcells, are found in both fundic and pyloric mucosas. 4

5 Ulcers. Animal Science 126 Equine Nutrition Ulcers Equine gastric ulcer syndrome (EGUS) is a condition characterized by ulcers in the terminal esophagus, the proximal (squamous) stomach; distal (glandular) stomach and the proximal duodenum. 80% of ulcers occur in the proximal third of the stomach which is lined by non-glandular squamous cells. The remaining 2/3rds is lined by glandular cells that secrete protective mucus and bicarbonate. 90% race horses and 60% show horses thought to have ulcers Fiber in the diet forms a mat Some horses though produce too much gastric acid especially when stressed by shipping, showing or training regimes. Ulcers Cont. Horses naturally do not spend much time moving any faster than a walk. All ages and breeds are susceptible and current pharmacologic treatments focus on blocking gastric acid secretion and raising ph. Nutrition and management have an important role and can be used to decrease severity and recurrence. History, clinical signs, and response to treatment are all indicators of ulcers, however the only definitive diagnosis is gastroscopy using an endoscope. 5

6 Ulcers Cont. Risk factors for EGUS include; Intense exercise especially on an empty stomach Intermittent versus continuous feeding Stall confinement Clinical signs include; Poor performance Poor coat Picky eating Colic Cribbing Severity of ulcers tends to increase with severity of symptoms and ulcers have been shown to be diagnosed in 88%-92% of horses with a client complaint of conditions associated with ulcers or subtle signs of poor health compared to 37 to 52% identification in horses not showing symptoms. (Reese and Andrews 2009) Reese, R.E., and Andres, F.M. Nutrition and Dietary Management of equine gastric ulcer syndrome. Vet Clinic Equine 25(2009)79-92 Ulcers Management. Pharmacologic (drug) therapy may be necessary to heal both kinds of ulcers but once discontinued the ulcer will likely return if management changes are not implemented. Modification of exercise intensity and duration Pasture turnout Increase forage and fiber in the diet Eliminate feeding few large meals and feed smaller more frequent meals Decrease concentrate feed sizes Calcium carbonate supplements Feeding alfalfa as some of the forage in the diet(high calcium and protein levels are thought to help buffer stomach acid Dietary supplements 6