Veterinary Anatomy: Forestomach and Bloat

Forestomach

• The forestomach consists of the rumen, reticulum, and omasum.
• Lined by stratified squamous epithelium.
• Examination of plant contents within the rumen can provide insights into potential toxicities.

Ruminal Tympany (Bloat)

• Over-distension of the rumen and reticulum with fermentation gases.
• Primary (Frothy Bloat):
  • Gases trapped in bubbles within rumen contents.
  • Common causes include:
    • Legumes (white clover, alfalfa, red clover) with high soluble protein content.
    • High grain diets, which reduce salivation (saliva has anti-foaming properties).
• Secondary (Free Gas Bloat):
  • Blockage in the eructation mechanism, such as:
    • Obstruction in the esophagus.
    • Vagal indigestion, where rumen motility is inhibited due to vagal nerve damage.
  • Characterized by excess gas without foam.

Bloat - Cause of Death

• Pressure from the expanding rumen compresses the thorax, leading to:
  • Compression of the vena cava, resulting in poor venous return.
  • Cardiac arrest.
• Grossly, bloated animals found dead will often be rolled on their backs, with:
  • Abdominal distension.
  • Marked congestion of the head and neck.
  • A "bloat line" on the esophagus at the thoracic inlet, where the caudal (white) and cranial (congested) mucosa of the esophagus meet.

Rumen Contents

• The rumen is greatly enlarged during bloat and contains food mixed with numerous gas bubbles.
• Foreign bodies can accumulate in the rumen, including:
  • Trichobezoars: Hair balls.
  • Phytobezoars: Plant balls.
  • Lead substances: Can cause poisoning.
  • Sharp metals: Dangerous due to their potential for penetration and migration.

Sharp Metals - Fate and Complications

• Sharp metallic objects often deposit in the reticulum, causing various complications:
  • Localized Reticulitis: Inflammation of the reticulum itself.
  • Traumatic Reticulopericarditis: Penetration of the reticulum, diaphragm, and pericardial sac.
  • Vagal Indigestion: Penetration of the reticulum, damaging the vagus nerve, resulting in impaired rumen motility.

Inflammation of the Forestomach

• Causes:
  • Extension from oral and esophageal infections.
  • Grain overload, leading to ruminal lactic acidosis.
• Pathogenesis:
  • Sudden change to high carbohydrate diets leads to:
    • Overgrowth of gram-positive bacteria.
    • Increased production of lactic and dissociated fatty acids, lowering the rumen pH.
    • Ruminal atony (weakness) and mucosal damage.
    • Fluid shifts from blood into the rumen.
• Complications:
  • Sudden death due to dehydration, acidosis, and endotoxemia.

Grain Overload - Ovine (Sheep)

• Marked hyperemia, erosion, and multiple confluent vesicles are observed in the ruminal mucosa.
• Multiple ulcers are commonly found in the ruminal mucosa.

Sequelae of Forestomach Inflammation

• Bacterial Rumenitis:
  • Commonly caused by Fusobacterium necrophorum.
  • Healed ulcers may leave stellate scars (star-shaped).
• Liver Abscesses:
  • May rupture into the vena cava, causing fatal septic embolism.
• Mycotic Rumenitis:
  • Characterized by well-demarcated, circular hemorrhagic infarcts.
  • Can become systemic, potentially causing placentitis (infection of the placenta) and abortion.

Ulcers on the Rumen Pillars

• Commonly observed in cattle and sheep.
• Differential diagnosis is necessary to determine the cause.

Acute Gastric Dilation and Volvulus (GDV)

• Predominantly occurs in large dog breeds.
• Triggers:
  • Large meals (dry or highly fermentable).
  • Failure of eructation and pyloric outflow (the opening between the stomach and small intestines).
• Pathogenesis:
  • Gas accumulation leads to functional obstruction of the cardia (entrance to the stomach) and pylorus.
  • Gastric dilation occurs.
  • The stomach rotates on its mesenteric axis (volvulus).
• Complications:
  • Compression of the diaphragm and vena cava, reducing venous return and cardiac output.

Abomasal Displacement

• Left Abomasal Displacement:
  • Most frequent in dairy cows, particularly older, high-producing animals in the post-calving period.
  • A common gastrointestinal disorder that often requires surgery, but is rarely fatal.
• Right Abomasal Displacement:
  • Less common, occurring in about 15% of cows and calves.

Gastric/Abomasal Impaction

• Causes:
  • Low-quality roughage.
  • Low water intake.
  • Poor mastication.
  • Vagal nerve damage.
  • Pyloric stenosis (narrowing of the pyloric opening).

Gastric Dilation and Rupture

• Predominantly occurs in horses.
• Factors:
  • Fermentable carbohydrates.
  • Secondary to intestinal obstructions.
  • Equine dysautonomia (a disorder affecting the autonomic nervous system).
• Distinction:
  • Ante mortem (before death) rupture from post mortem (after death) rupture.

Gastric Ulcers

• While less common than in humans, gastric ulcers are significant in animals.
• Imbalance between acid secretion and mucosal protection (gastric mucosal barrier) is a key contributor.
• Pathogenesis:
  • Epithelial necrosis (cell death) leads to erosion, ulceration, bleeding, and potentially perforation, leading to peritonitis (inflammation of the abdominal lining ).

Gastric Ulcers - Causes

• Local mucosal injury.
• High gastric acidity.
• Local ischemia (reduced blood flow, causing stress ulcers).
• Steroids and NSAIDs (e.g., aspirin).
• Helicobacter (bacterial infection).

Gastric Ulcers - Main Signs

• Hematemesis (vomiting blood).
• Melena (dark, tarry stools due to digested blood).
• Anemia (low red blood cell count).
• Abdominal pain.

Gastritis

• Cattle, Sheep, and Goats:
  • Clostridium septicum (causing Braxy or bradsot).
  • Clostridium perfringens type A (leading to abomasitis with ulceration).
  • Mycotic infections.
• Dogs and Cats:
  • Uremia (elevated blood urea nitrogen).
  • Chronic gastritis and hypertrophy (enlargement) of the stomach.
  • Helicobacter infections.

Parasitic Diseases

• Ruminants:
  • Haemonchus (haemonchosis).
  • Ostertagia (ostertagiosis, causing lymphoid hyperplasia, an overgrowth of lymphoid tissue).
  • Trichostrongylus (trichostrongylosis).
• Equine:
  • Gastric bots (larvae of certain flies).
  • Trichostrongylus (trichostrongylosis).
  • Draschia megastoma (a parasitic worm).
  • Habronema (parasitic nematodes).

Congenital Anomalies

• Atresia:
  • Absence of a normal opening.
  • Example: Atresia ani (absence of an anus).

Intestinal Displacements and Malposition: Hernias

• Hernia: Protrusion of an organ through a natural or artificial opening.
• Types:
  • Internal:
    • Diaphragmatic hernia (through the diaphragm).
  • External:
    • Ventral hernia (on the abdominal wall).
    • Umbilical hernia (at the navel).
    • Scrotal hernia (in the scrotum).

Hernia Sequelae

• Complications:
  • Strangulation: Interference with blood flow due to constriction of the hernia.
  • Adynamic ileus: Paralysis of the intestines.
  • Perforation: A hole in the intestinal wall.

Strangulation - Complications

• Strangulation obstructs venous return, leading to:
  • Congestion.
  • Necrosis (tissue death).
  • Bacterial invasion.
• Ultimately, strangulated hernias can cause shock and septicemia (blood poisoning).

Torsion and Volvulus

• Torsion: Rotation of an organ around its long axis.
• Volvulus: Twisting of an organ around its mesentery, which can strangle the blood supply.
• Mesenteric lipomas (fatty tumors) can wrap around the mesentery or bowel, causing strangulation.

Intussusception

• Telescoping of one segment of bowel into another adjacent section.

Enteritis

• Inflammation of the intestines.
• Terms:
  • Enteritis: Inflammation of the small intestine.
  • Typhlitis: Inflammation of the cecum (first part of the large intestine).
  • Colitis: Inflammation of the large intestine.
  • Enterocolitis: Inflammation of the entire intestines.
  • Gastroenteritis: Inflammation of the stomach and small intestines.
  • Proctitis: Inflammation of the rectum.

Diarrhea and Dysentery

• Diarrhea: Increased stool mass, frequency, and/or fluidity.
• Dysentery: Painful, bloody diarrhea.

Pathogenesis of Diarrhea: Causes

• Malabsorption: Defective digestion or absorption.
• Osmotic diarrhea: Caused by luminal solutes (substances in the intestinal lumen) drawing fluid into the intestines.
• Hypersecretion: Excessive intestinal fluid secretion triggered by enterotoxins.
• Exudation: Increased capillary or epithelial permeability, leading to fluid leakage into the intestines.

Enteritis - Types of Inflammation

• Catarrhal: Characterized by mucus. Often associated with viral diseases.
• Hemorrhagic: Bleeding in the intestinal tract. Often associated with bacterial diseases.
• Fibrinous/fibrinonecrotic: Inflammation with fibrin deposition and tissue death. Often associated with mycotic (fungal) diseases.
• Ulcerative: Inflammation with ulcer formation. Often associated with protozoal diseases or parasites.
• Proliferative/hyperplastic: Increased cell growth. Often associated with parasitic diseases.
• Granulomatous: Formation of granulomas (small, tumor-like nodules) in the intestinal wall. Often associated with noninfectious diseases.

This quiz dives into the anatomy of the forestomach, including the rumen, reticulum, and omasum. It covers conditions such as ruminal tympany (bloat), exploring the primary and secondary causes, as well as their implications for animal health. Test your knowledge on this crucial aspect of veterinary anatomy!