Digestive System

Question 1

Lips?

Answer 1

Lips?

.Prehensile and very sensitive.

.Used by the horse to aid food selection and prevent the ingestion of harmful material.

.Are capable of selecting individual ingredients out of a course mix or eating the last blades of grass from around a poisonous plant without touching it.

Question 2

Tongue?

Answer 2

Tongue?

.Forms the food into a bolus (ball)

.Long and soft

.Taste buds present can detect sweet, sour, bitter and salt flavours.

Question 3

Salivary glands?

Answer 3

Salivary glands?

.The saliva starts the breakdown of starch and provides the moisture to create the bolus (ball of food) for swallowing into the oesophagus.

.Horses secrete 10 - 15 litres of saliva per day to lubricate food.

. Major salivary glands - parotid, mandibular (submaxillary) & sublingual salivary glands.

.A small amount of salivary amylase is secreted but is probably of little important as there is little digestion that occurs in the stomach.

. Bicarbonate is also secreted which has some buffering capacity.

Question 4

Hard palate?

Answer 4

Hard palate?

Question 5

Soft palate?

Answer 5

Soft palate?

.Very long & at rest it hangs down in front of the epiglottis making mouth breathing difficult & normal vomiting impossible.

Question 6

Pharynx?

Answer 6

Pharynx?

.Guttural pouches are here and only found in the horse.

Question 7

Oesophagus?

Answer 7

Oesophagus?

.A muscular tube that starts at the end of the pharynx and ends at the cardia of the stomach. It moves food from the mouth to the stomach.

.Passes down the left side of the neck. The passage of food and water may easily be observed.

.About 1.5m in length in mature horses and has very little reflux capacity that can lead to choke.

Question 8

Stomach?

Answer 8

Stomach?

.The stomach is where the food is broken down by acids and enzymes then it’s sent to the small intestines .

.Digestion is monogastric as in the cat and dog.

.Stomach is (7-14L) small compared with the size of the horse.

.Naturally the horse would graze for a large proportion of the day and food would continually enter and leave the stomach with little actual digestion occuring apart from the initial breakdown of protein.

.In the stabled horse the stomach fills rapidly when a concentrate meal is fed and then acts as a storage organ, enabling food to enter the small intestine in small quantities for maximum digestion.

Question 9

Small intestine?

Answer 9

Small intestine?

.Parts - duodenum, jejunum and ileum which ends at the ileocaecal junction.

.The nutrients from the food are absorbed here and sent to the caecum.

.Responsible for the majority of enzymatic digestion of food and it’s subsequent absorption.

.About 16m and accounts for around 75% of the length of the GI tract, but only 27% of its volume.

.Digesta moves rapidly along the small intestine but, despite this, under normal circumstances digestion and absorption of soluble material are usually complete by the time it reaches the ileocaecal junction.

Question 10

Large intestine (hindgut)?

Answer 10

Large intestine (hindgut)?

.The large intestine starts at the caecum which is where the fibre in the diet is broken down by millions of bacteria and this process carries on through the large colon.

.Fibre digestion takes place here, undergoing a microbial fermentation similar to that seen in ruminants and rabbits. It accounts for around 65% of the volume of the digestive tract.

.Main areas involved in this process are the caecum & colon. The size & complexity of the hindgut are what makes it different from other monogastric animals.

.Has the largest & most complex large intestine of all domestic animals. Folded many times & can become obstructed or displaced which leads to colic.

Question 11

Microbial activity in hindgut?

Answer 11

Microbial activity in hindgut?

.A horse is capable of living on a diet solely of fibrous roughage and a large population of microorganisms is housed in the enlarged hindgut. Fungi are also present but in much smaller numbers.

.Microbial enzymes are capable of breaking the B - 1, 4 linkages found in cellulose, unlike mammalian enzymes and produce end - products of volatile fatty acids and lactic acid, which can be absorbed directly from the hindgut.

.Other products of microbial fermentation of potential use are amino acids and vitamins.

.The microorganisms in the hindgut are very specific to the type of food eaten by the horse and also to the pattern of meals eaten when the horse is fed concentrates.

Question 12

Teeth?

Answer 12

Teeth?

.All the same height, deep-rooted

.Function is to grasp and tear food into smaller pieces to be able to swallow. The incisors tear & cut the grass, the molars grind.

.They have hypsodontic teeth i.e. they don’t have a surface covering of enamel.

.Worn down by 2-3mm per year by eating and can form edges that need filling down by a vet or dentist to be able to eat properly.

.Space between incisors and premolars is called the diastema which aids the separation of newly ingested and partly masticated food.

Question 13

Number of teeth?

Answer 13

Number of teeth?

.Foals are normally born without teeth and the central incisors erupt during the first week of life and the rest deciduous by 6-9 month. Replaced by permanent teeth between 2.5 - 4.5 years.

.Deciduous teeth -24

.Permanent teeth = male 40 - 42, female 36 - 40

• Incisors 6 upper & lower
• Premolars 3 upper and lower
• 3 upper and lower molars
• If present 2 upper & lower canine teeth (tushes) erupt at 4-5 years
• If present 2 upper & lower extra premolar teeth (wolf teeth)

Question 14

Large intestine parts?

Answer 14

Large intestine parts?

.Large colon

.Small colon

.Rectum

.Anus

Question 15

Caecum?

Answer 15

Caecum?

.Large (25 - 35L) blind ending sac about 0.8m long, running forwards along the base of the abdomen, and it’s here that food entering from the ileum starts to undergo microbial fermentation.

.The digesta contains around 90% water but by the time defecation occurs the water content has fallen to about 60%, the largest proportion of water being reabsorbed in the caecum.

Question 16

Large colon?

Answer 16

Large colon?

.Mainly concerned with the digestion of fibre.

.Approx 3 - 3.5m long, however parts of the large colon are up to 50cm in diameter.

.It houses a considerable number of microorganisms.

.It runs from the ileocaecal junction cranially towards the sternum - the right ventral colon, where it makes a turn - sternal flexure, back towards the pelvis - left ventral colon, then a sharp turn - the pelvis flexure forwards again towards the diaphragm - left dorsal colon, and then backwards again - diaphragmatic flexure and right dorsal colon. Finally, the large colon makes another turn and crosses from one side to the other - transverse colon - before becoming the small colon.

Question 17

Small colon?

Answer 17

.Small colon?

.The small colon is where the faeces are made and are sent to the rectum to be store.

.The small colon is approx 3 - 3.5m long and 7.5cm in diameter.

.Microbial fermentation does not stop here; however it is of less important and the main function of the small colon is to slow the passage of digesta and reabsorb water to enable relatively dry faeces to be voided.

Question 18

Colic?

Answer 18

Colic?

.The pelvic flexure where the large colon narrows from a diameter of about 25cm to around 2cm while undergoing a 180° turn.

.In the grass fed horse this serves to slow down the passage of food, allowing ample time for microbial digestion, however in the stabled horse fed a much drier diet and unable to move around freely, it can sometimes be the site of an impaction which leads to colic and may need surgery to fix.

.Signs - may be stops eating, looks round at belly, stamping at the ground, kicking belly, lying down. In acute pain it will roll over repeatedly, pulse may increase to 60 or 80bpm.

Question 19

Mouth parts?

Answer 19

Mouth parts?

.Is where ingestion takes place. With the help of the teeth and tongue they break down the food into smaller pieces and the salivary glands secrete saliva to lubricate the food making it easier to swallow.

• Lips
• Teeth
• Tongue
• Hard palate
• Soft palate
• Pharynx
• Guttural pouches
• Salivary glands

Question 20

Foregut parts?

Answer 20

Foregut parts?

• Oesophagus
• Stomach
• Small intestine = duodenum, jejunum, and ileum.

.The foregut of the horse is much like those of other monogastric (simple - stomached) animals such as humans, pigs, and dogs.

Question 21

Hindgut parts?

Answer 21

Hindgut parts?

• Caecum
• Large colon
• Small colon
• Rectum

.The horse is unique in that most of the digestion of their feed occurs in the hindgut through the process of fermentation with the help of billions of naturally occurring bacteria and protozoa (together known as microbes).

Question 22

Rectum & anus?

Answer 22

Rectum & anus?

.Rectum acts as a storage area for faeces, as in other mammals.

.Horses defecate frequently throughout the day and night, maintaining a constant throughput of material through the GI tract.

Question 23

Changing diet suddenly?

Answer 23

Changing diet suddenly?

.Can result in the death of large numbers of microorganisms that were digesting the old food stuff and an insufficient number capable of digesting the new foodstuff.

.Such changes in diet can result in impaction, colic, laminitis and swollen legs.

Question 24

Eating faeces?

Answer 24

Eating faeces?

.Foals may eat the faeces of their mothers. This may be done in an attempt to populate the hindgut with suitable microorganisms.

Question 25

Pancreas?

Answer 25

Pancreas?

.Two functions the endocrine & exocrine.

.The exocrine part is used for digestion because it produces digestive juices that are rich in enzymes to be sent to the duodenum for breaking down nutrients.

.Produces and regulates the release of insulin, a hormone that functions to metabolise and balance the body’s main source of fuel, glucose. Glucose is a sugar converted from carbohydrates in forage & grain.

.Insulin helps cells absorb glucose and turns any excess glucose into glycogen, an insoluble sugar which is stored in the liver until needed.

Question 26

Microbial Fermentation?

Answer 26

Microbial Fermentation?

.The enzymatic decomposition and utililization of foodstuffs, particularly carbohydrates, by microbes. Fermentation takes place throughout the gastrointestinal tract of all animals, but the intensity of fermentation depends on microbe numbers, which are generally highest in the large bowel. Thus, the large intestine is quantitatively the most important site of fermention, except for species with forestomachs (ruminants).

.Digestion and metabolism of carbohydrates not digested in the small intestine (e.g. cellulose, residual starch)

.Importantly, the major end products of microbial digestion of cellulose and other carbohydrates are volatile fatty acids, lactic acid, methane, hydrogen and carbon dioxide. Fermentation is thus the major source of intestinal gas.

Question 27

Cardiac sphincter?

Answer 27

Cardiac sphincter?

.Small ring muscle that allows food into the stomach.

Question 28

Gastric juice?

Answer 28

Gastric juice?

.Is stimulated by the arrival of food into the stomach. Produces (10-30L) daily.

Question 29

Pyloric sphincter?

Answer 29

Pyloric sphincter?

.Muscle ring at the end of the stomach which moves food to the small intestine this stage is called chyme.

Question 30

Jejunum?

Answer 30

Jejunum?

.Approx 20m long

.Amino acids, vitamins minerals & glucose are absorbed into the bloodstream.

.Fatty acids & glyceral are taken up by a separate system called the lymphatic system as minute globules to distribute fat around the body by the vascular system.

Question 31

Duodenum?

.Approx 1m long & forms an S shape bend.

.Into it flows bile secreted by the liver & pancreatic juices.

Answer 31

Duodenum?

.Approx 1m long & forms an S shape bend.

.Into it flows bile secreted by the liver & pancreatic juices.