Equine & Bovine Oral Cavity and Tongue

• Learning objectives include dental terminology and formula for horses and cows, luminal organs of the gastrointestinal tract and order of food passage ("peristalsis"), and major differences in gastrointestinal organs between Equine and Bovine.

Oral Cavity in Large Animals

• It has 2 segments similar to smaller animals: oral vestibule and oral cavity proper.
• The soft palate in horses is very long, and hangs down before the epiglottis.
• Its free margin is closely applied to the tongue.
• Ruminants do not have upper incisor teeth.
• At the level of the inner face of the lips and cheeks are buccal papillae (3).

The Tongue

• In horses it is long and spatulate at its apex.
• The upper surface is covered with delicate filiform papillae that confer a velvet-like texture
• It also features vallate papillae (10), foliate papillae (9) and fungiform papillae (11).
• The caudal part of the tongue in ruminants is raised, forming the lingual torus (3).
• The rostral part features the lingual fossa.
• The dorsal aspect of the tongue is strongly keratinized, and filiform papillae (b) are keratinized
• Fungiform papillae (c) are located along the edges of the apex and body and are scattered between the filiform papillae.
• Vallate papillae (f, g) number from 8-21 in cattle on each side
• Foliate papillae do not exist in ruminants.
• Lenticular and conical papillae (e) cover the lingual torus in ruminants.

Dentition

• The teeth have short crowns, well-developed roots, and an obvious division between the crown and root (carnivores/humans: Brachydont).
• The teeth are high-crowned with enamel extending deep to the gum line, providing extra material for future eruption and wear (Ruminants/Equine: Hypsodont)
• Dental formula in horses: 3-1-3(4)-3/3-1-3-3
• The wide gap that separates the incisors from the cheek teeth is called the Diastema (2) and it may be interrupted by the canine tooth
• The Triadan numbering System is used for dentition.
• Wolf teeth are a component of the permanent dentition, and is the first premolar P1, though it often fails to develop.
• This is almost invariably confined to the upper jaw, and is without functional significance, so it is easily extracted.
• Dental formula in Cattles: 0-0-3-3/3-1-3-3
• There is an absence of incisor and canine teeth in the upper jaw in cattle
• The assimilation of the canines to the incisors in the lower jaw happens in cattle
• The fourth or corner incisor also features in cattle
• Upper and lower first premolar teeth fail to develop

Dental Pads

• The upper incisors in both large and small ruminants are replaced by dental pads (2).

Equine Stomach

• A simple stomach that is small in size, proportionate to the animal and volume of fodder consumed
• The interior is divided in 2 areas (Non-glandular and Glandular), and the border between them is demarcated by the margo plicatus (4)
• The non-glandular part is covered by squamous epithelium.
• The glandular part is covered by glandular mucosa.
• The cardiac sphincter is well developed, preventing the horse from eructating or vomiting
• Margo plicatus and the pyloric segment can be parasitized by botfly larvae

Bovine Stomach

• Composed of 4 chambers: Rumen (4), Reticulum (1), Omasum (2), and Abomasum (3)
• Rumen, reticulum and omasum are known as forestomach.
• The rumen (4) is a huge fermentation chamber that is placed on the left side of the abdominal cavity
• It extends from the cardia to the pelvic inlet, and continues with the reticulum through the rumino-reticular orifice
• Longitudinal grooves divides it into a dorsal ruminal sac and a ventral ruminal sac.
• The reticulum (1) is the second forestomach, placed on the left side of the abdominal cavity
• It is cranially bordered by the diaphragm muscle and caudally bordered by the rumen.
• It communicates with the rumen and omasum though the rumino-reticular orifice and the reticulo-omasal orifice respectively.
• The reticular mucosa has a honeycomb appearance.
• The omasum (2) is the third forestomach and is placed on the right side of the abdominal cavity
• It is spherical in shape with greater and lesser curvature
• It communicated with the reticulum (reticulo-omasal) and abomasum (omasoabomasal).
• It is under the cover of the 8th – 11th ribs
• The abomasum (3) is the last compartment of the bovine stomach.
• It resembles the monogastric stomach most closely, and is found on the right side of the abdominal cavity.
• It is shaped like an elongated sac that is in direct contact with the abdominal floor.
• It has three segments (fundus, body, and pyloric part) that are lined by glandular mucosa.
• It continues with the duodenum.

Intestine Segments

• The small intestine has various segments.
• The gastrointestinal tracts consists of the stomach, small intestine, cecum, ascending colon, and descending colon

Large Intestine in Horses

• The cecum is the first segment of the large intestine that is placed on the right side of the abdomen
• It occupies the right flank region and is shaped like a comma.
• 3 segments include the base, body and a ventral blind apex, four teniae coli, and two orifices.
• The two orifices are the ileocecal orifice and cecoclic orifice
• The colon has three segments: ascending colon, transverse colon and descending colon
• The ascending and transverse colon combines to form the large colon, while the descending colon is known as the small colon.
• The ascending colon has four parallel limbs and three flexures.
• Right ventral colon (RVC) and Ventral diaphragmatic flexure (VDF).
• Left ventral colon (LVC) and Pelvic flexure (PF).
• Left dorsal colon (LDC) and Dorsal diaphragmatic flexure (DDF).
• Right dorsal colon (RDC).

Large Intestine in Ruminants

• The cecum is placed in the dorsal part of the right flank region having a cylindrical shape.
• The cecum is approximately 50-70 cm in length.
• Parts of the cecum including the body and apex can be identified.
• The cecum is directly connected to the proximal loop of the ascending colon.
• lleocecal fold or ligament can be seen between the cecum and the ileum.
• The colon is divided into the ascending, transverse, and descending colon
• The ascending colon is lengthy and has a flat spiral apperance and has 3 segments including the proximal loop, spiral loop, and distal loop
• The transverse and decending regions are short in ruminants.

Liver in Horses

• It is located in the most cranial part of the abdomen immediately caudal to the diaphragm muscle with an oblique position.
• The liver consists of four hepatic lobes: right hepatic lobe (1), left hepatic lobe (2), quadrate hepatic lobe (3), and caudate lobe (4).
• Horses do not have a gall bladder.

Liver in Ruminants

• The liver is located on the right side of the median plane, and is also caudal to the diaphragm muscle with an oblique position
• The four hepatic lobes include the right, left, quadrate, and caudate lobes.
• The gall bladder is well developed in cattle.

Pancreas in Horses

• The pancreas has three segments (body, a left lobe that is long, a right lobe that is short), and 2 ducts
• The body of pancreas is perforated by the portal vein (f)
• The 2 ducts are the pancreatic duct (d), and the accessory pancreatic duct (e).

Pancreas in Ruminants

• The bovine's pancreas has 3 segments and has the accessory pancratic duct.
• The segments include the body (notched by the portal vein), along with the left and right lobes.
• Sheep and goats only have the pancreatic duct.