Horse (Equus ferus caballus)
Introduction:
the Horse is a mammal that belongs to the Equidae family. The horse has evolved over the last 45 to 55 million years into the large signal toed creature we know today. Horses were domesticated around 4000 BC and until the the 20th century horses were primarily used as a source of transportation and work. Today the horse's main job is to be an athlete as well as a companion for humans [1].
Domesticated horses are within the subspecies called caballus. As an animal of prey horses have evolved into escape artists. Their anatomy allows them to run speeds around 40 mph. Although, speed largely depends on the breed; while Thoroughbreds can run roughly 45 mph, Quarter horses can reach speeds of 50 mph over short distances [2]. Horses have also developed an astounding sense of balance and a strong fight-or-flight response allowing them to survive. This amazing sense of balance allows horses to sleep standing up or lying down.
A horse's gestation period is 11 months long, they reach adulthood by the age of 5 years old, and their life span is roughly 25 to 30 years [1].
People commonly divide horses into three subgroups: "hot bloods", "cold bloods", and "warmbloods". "Hot blood" are horses with speed and endurance such as: Arabians and Thoroughbreds. Draft horses and ponies are usually classified as "cold bloods" and referred to as the strong and slow breeds. "Warmbloods" are a cross between "cold bloods" and "hot bloods" and are chiefly used for sporting events such as show jumping [1].
The horse is an herbivore
A horse's natural diet consist of only plants. they are known as "grazers" meaning they eat small amount grass throughout the entire day. Although this is true for horses out in the wild, domesticated horses often have diets formulated with grain and hay and are only fed twice a day [3].
the Horse is a mammal that belongs to the Equidae family. The horse has evolved over the last 45 to 55 million years into the large signal toed creature we know today. Horses were domesticated around 4000 BC and until the the 20th century horses were primarily used as a source of transportation and work. Today the horse's main job is to be an athlete as well as a companion for humans [1].
Domesticated horses are within the subspecies called caballus. As an animal of prey horses have evolved into escape artists. Their anatomy allows them to run speeds around 40 mph. Although, speed largely depends on the breed; while Thoroughbreds can run roughly 45 mph, Quarter horses can reach speeds of 50 mph over short distances [2]. Horses have also developed an astounding sense of balance and a strong fight-or-flight response allowing them to survive. This amazing sense of balance allows horses to sleep standing up or lying down.
A horse's gestation period is 11 months long, they reach adulthood by the age of 5 years old, and their life span is roughly 25 to 30 years [1].
People commonly divide horses into three subgroups: "hot bloods", "cold bloods", and "warmbloods". "Hot blood" are horses with speed and endurance such as: Arabians and Thoroughbreds. Draft horses and ponies are usually classified as "cold bloods" and referred to as the strong and slow breeds. "Warmbloods" are a cross between "cold bloods" and "hot bloods" and are chiefly used for sporting events such as show jumping [1].
The horse is an herbivore
A horse's natural diet consist of only plants. they are known as "grazers" meaning they eat small amount grass throughout the entire day. Although this is true for horses out in the wild, domesticated horses often have diets formulated with grain and hay and are only fed twice a day [3].
Horse Digestive System
Evolution of a horse's digestive tract
Horses are monogastrics (only have one stomach) just like humans and tigers but unlike humans and tigers, horse are known as "hindgut fermenters". This means they can digest highly fibrous plants such as grass and hay that consist largely of cellulose. Cellulose is nearly impossible to digest but can be done with the aid of microbes. Unlike ruminants (animals with 4 chambered stomachs) where digestion of cellulose occurs in the stomach, horse microbial fermentation occurs in a part of their large intestine known as the cecum, this type of microbial fermentation is also known as post gastric microbial fermentation [3].
Horses evolved into "hindgut ferementers" because they are incapable of vomiting. This inability to vomit prevented them from regurgitating food and "chewing their cud" like all ruminants do. Being a "hindgut fermenter" allows horses to survive off of grass without wasting hours each day "chewing their cud" [3].
Anatomy and Physiology [4]
Horses' Digestive systems are long, complex, and slow mainly due to microbial fermentation. This microbial fermentation allows highly fibrous feeds such as hay and grass to be digested. To better understand the physiology of a horse's digestive system the anatomy and function of their digestive system must be taken into consideration.
Mouth- The mouth is the first part of a horses digestive system and it includes: Teeth, lips, and a tongue used for grabbing feed as well as breaking down the particle size of feed. Unlike most mammals a horse's saliva does not include any enzymes.
Esophagus- Is a 50 to 60 inch tube that transfers feed from the mouth to the stomach. The esophagus in a horse only moves towards the stomach, this one directional movement prevents horses from vomiting/regurgitating.
Stomach- Horses have a small stomach (3 to 4 gallons) in comparison to their size. The purpose of the stomach in most mammals is to mix feed and secrete acid to further break down feed particles . A horse's stomach does very little mixing and ingesta will usually arrange in layers.
Small Intestine- The small intestine is a long tube which is most active in digestion and nutrient absorption. It includes the duodenum, jejunum, and ileum. The small intestine is surrounded by the pancreas and liver. One significant difference between horses and other mammals is that horses do NOT have gallbladders.
Large intestine- The horse's large intestine makes up 60% of its digestive system. The large intestine is divided into the cecum, large colon, small colon and the rectum. The primary function of the small colon is water re-absorption and mineral secretion as well as the secretion of waste.
Cecum- Contains large populations of microbial life that can break down cellulose (fibrous part of grass) into nutrients the horse can absorb. The cecum also plays an important role in temperature regulation. A by product of microbial fermentation is heat and it is used to regulate body temperature.
Evolution of a horse's digestive tract
Horses are monogastrics (only have one stomach) just like humans and tigers but unlike humans and tigers, horse are known as "hindgut fermenters". This means they can digest highly fibrous plants such as grass and hay that consist largely of cellulose. Cellulose is nearly impossible to digest but can be done with the aid of microbes. Unlike ruminants (animals with 4 chambered stomachs) where digestion of cellulose occurs in the stomach, horse microbial fermentation occurs in a part of their large intestine known as the cecum, this type of microbial fermentation is also known as post gastric microbial fermentation [3].
Horses evolved into "hindgut ferementers" because they are incapable of vomiting. This inability to vomit prevented them from regurgitating food and "chewing their cud" like all ruminants do. Being a "hindgut fermenter" allows horses to survive off of grass without wasting hours each day "chewing their cud" [3].
Anatomy and Physiology [4]
Horses' Digestive systems are long, complex, and slow mainly due to microbial fermentation. This microbial fermentation allows highly fibrous feeds such as hay and grass to be digested. To better understand the physiology of a horse's digestive system the anatomy and function of their digestive system must be taken into consideration.
Mouth- The mouth is the first part of a horses digestive system and it includes: Teeth, lips, and a tongue used for grabbing feed as well as breaking down the particle size of feed. Unlike most mammals a horse's saliva does not include any enzymes.
Esophagus- Is a 50 to 60 inch tube that transfers feed from the mouth to the stomach. The esophagus in a horse only moves towards the stomach, this one directional movement prevents horses from vomiting/regurgitating.
Stomach- Horses have a small stomach (3 to 4 gallons) in comparison to their size. The purpose of the stomach in most mammals is to mix feed and secrete acid to further break down feed particles . A horse's stomach does very little mixing and ingesta will usually arrange in layers.
Small Intestine- The small intestine is a long tube which is most active in digestion and nutrient absorption. It includes the duodenum, jejunum, and ileum. The small intestine is surrounded by the pancreas and liver. One significant difference between horses and other mammals is that horses do NOT have gallbladders.
Large intestine- The horse's large intestine makes up 60% of its digestive system. The large intestine is divided into the cecum, large colon, small colon and the rectum. The primary function of the small colon is water re-absorption and mineral secretion as well as the secretion of waste.
Cecum- Contains large populations of microbial life that can break down cellulose (fibrous part of grass) into nutrients the horse can absorb. The cecum also plays an important role in temperature regulation. A by product of microbial fermentation is heat and it is used to regulate body temperature.
Physiology Continued[4]
Physiology refers to how the body functions as well as maintaining homeostasis. The physiology of a horse's digestive system includes the glands and secretions need for nutrient digestion and absorption.
Physiology of the mouth: Horses have salivary glands in their mouths that secrete saliva. Saliva contains water to moisten feed, mucus to lubricate feed, and inorganic salts such as bicarbonate to regulate the pH of the stomach. ~homeostasis~
**Most mammals secrete enzymes in their saliva but horses do not.
Physiology of the stomach: the stomach secretes many digestive juices need for the digestion of feed. these include:
Hydrochloric acid (HCl)- HCl is a strong acid required to activate certain enzymes. HCl is also secreted to kill bacteria and microbes that enters the stomach.
Mucus- the stomach lumen secretes mucus to protect the stomach walls from HCl.
Pepsin- pepsin is a enzyme required to break down protein and is activated by HCl.
Physiology of the liver in the digestive system: The purpose of the liver in the GI tract is to produce and secrete bile. horses do not have gallbladders and their bile is secreted directly from the liver into the small intestine.
Bile- is comprised mostly of water and alkaline salts. The alkaline salts in bile are used as buffers to regulate the pH of chyme entering the small intestine from the stomach. Bile is also required for fat digestion.
Physiology of the pancreas: The pancreas secretes pancreatic juices that aid in digestion from the pancreas into the duodenum through the pancreatic duct. these juices include: water, alkaline, trypsin, chymotrypsin, and carboxypeptidases
* *trypsin, chymotrypsin, and carboxypeptidases are enzymes required for protein degradation.
Absorption: Nutrients absorption can occur by passive transport in the intestinal lumen. A concentration gradient builds up in the blood vessels of the villi and micro-villi (protruding structures from the intestinal walls that increase surface area) creating a driving force that causes nutrients to enter the blood stream. Once nutrients enter the blood stream they can be transported by the blood to cells. The driving force for water absorption in the digestive system is osmosis and is dependent on the osmotic pressure in the blood [5].
Physiology refers to how the body functions as well as maintaining homeostasis. The physiology of a horse's digestive system includes the glands and secretions need for nutrient digestion and absorption.
Physiology of the mouth: Horses have salivary glands in their mouths that secrete saliva. Saliva contains water to moisten feed, mucus to lubricate feed, and inorganic salts such as bicarbonate to regulate the pH of the stomach. ~homeostasis~
**Most mammals secrete enzymes in their saliva but horses do not.
Physiology of the stomach: the stomach secretes many digestive juices need for the digestion of feed. these include:
Hydrochloric acid (HCl)- HCl is a strong acid required to activate certain enzymes. HCl is also secreted to kill bacteria and microbes that enters the stomach.
Mucus- the stomach lumen secretes mucus to protect the stomach walls from HCl.
Pepsin- pepsin is a enzyme required to break down protein and is activated by HCl.
Physiology of the liver in the digestive system: The purpose of the liver in the GI tract is to produce and secrete bile. horses do not have gallbladders and their bile is secreted directly from the liver into the small intestine.
Bile- is comprised mostly of water and alkaline salts. The alkaline salts in bile are used as buffers to regulate the pH of chyme entering the small intestine from the stomach. Bile is also required for fat digestion.
Physiology of the pancreas: The pancreas secretes pancreatic juices that aid in digestion from the pancreas into the duodenum through the pancreatic duct. these juices include: water, alkaline, trypsin, chymotrypsin, and carboxypeptidases
* *trypsin, chymotrypsin, and carboxypeptidases are enzymes required for protein degradation.
Absorption: Nutrients absorption can occur by passive transport in the intestinal lumen. A concentration gradient builds up in the blood vessels of the villi and micro-villi (protruding structures from the intestinal walls that increase surface area) creating a driving force that causes nutrients to enter the blood stream. Once nutrients enter the blood stream they can be transported by the blood to cells. The driving force for water absorption in the digestive system is osmosis and is dependent on the osmotic pressure in the blood [5].
References
[1] http://en.wikipedia.org/wiki/Horse
[2] http://www.saddleonline.com/blogs/content/how-fast-can-horse-run
[3] http://en.wikipedia.org/wiki/Equine_nutrition
[4] Marshall D Stern, University of Minnesota. Animal Nutrition 2401 lecture notes, fall 2014
[5] http://web.ics.purdue.edu/~smills/ANSC230/Digestive%20Physiology/Absorption.html
Video: http://www.youtube.com/watch?v=8lqk7igz9L4
[1] http://en.wikipedia.org/wiki/Horse
[2] http://www.saddleonline.com/blogs/content/how-fast-can-horse-run
[3] http://en.wikipedia.org/wiki/Equine_nutrition
[4] Marshall D Stern, University of Minnesota. Animal Nutrition 2401 lecture notes, fall 2014
[5] http://web.ics.purdue.edu/~smills/ANSC230/Digestive%20Physiology/Absorption.html
Video: http://www.youtube.com/watch?v=8lqk7igz9L4