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What is starch?

Starch is a very available storage carbohydrate found in horse feeds and forages.
More starch = more glucose, which means more sugar.


What are the names of the horse's ancestors?

The earliest is hyracotherium who lived about 55 million years ago
Mesohippus came next - 35 million years ago
Merychippus was after - 15 million years ago
Pliohippus - 8 million years ago
Then came the modern horse, Equus, which dates back to about 1 million years ago


What was the original diet of the horse's earliest ancestor?

The original diet of hyracotherium was soft shoots and berries. This was because they lived in the rainforest. They were able to consume a lot of sugar and readily available carbohydrates. They were meal feeders, often found alone due to predators.
Has brachyodont teeth, in which the enamel does not extend past the tooth root. This is the same as modern day humans.


What is the significance of a changing climate on the horse?

As the earth cooled, rainforests shrunk and gave way to open grassland and the horse evolved to survive on silica rich, fibrous grass. Their teeth evolved into hypsodont teeth, with enamel covering right down to the root, which needed grinding down by continually eating fibre. They became herd animals, grazing on open grassland for up to 18 hours a day (due to the low nutritional content of grass).


Define FERAL

Feral horses are horses descended from a domestic ancestor. They are not truly wild, but not domesticated either. An example would be the TBs released and still living in the Namibian desert.


How is a feral horse's time divided? How does this differ from a domesticated horse?

Feral horse:
60% eating, 20% standing, 10% lying down, 10% other

Domesticated horse:
15% eating, 65% standing, 15% lying down, 5% other


What is amylase? Where is it produced in the horse?

Amylase is an enzyme that breaks down starch in the small intestine. In the horse, it is produced in the pancreas


How much amylase is produced by the horse in comparison to other animals, such as a pig or a rat? What does this indicate?

Horse produces 2.3mg
Pig produces 107mg
Rat produces 56mg
This indicates that both the pig and the rat can cope with, and are designed to, eating lots of starchy, sugar rich foods. The horse is not - fibre should be the main component of the horse's diet.
REFERENCE: Lorenzo-Figueraz et al, 2007


What happens if a horse ingests a lot of starch?

If a lot of starch is consumed, the majority is dumped in the large intestine, because the small intestine cannot handle it all - this is a major cause of colic, laminitis and EMS



The glycaemic response is the effect that a meal has on blood sugar levels after consumption. It will elevate the blood sugar levels, but the amount will depend on the feed. It usually occurs about 2 hours after feeding. The glucosal peak is associated with abnormal behaviour


What parts of the brain are linked to the glycaemic response?

- the amygdala
- the hippocampus


Define the AMYGDALA

The amygdala is an almond shaped set of neurons located deep in the temporal lobe. It controls fear, anxiety and aggression. It is part of the limbic system and is the fight or flight centre.



The hippocampus is one of the brain's pleasure centres. It has the opposite function to the amygdala - one of the primary neurotransmitters in the hippocampus is serotonin


How is glucose linked with hippocampul serotonin?

- as glucose reached the blood stream, huge amounts of serotonin were released from the hippocampus
- an experiment in rats, where a glass tube was inserted into the brain to test hippocampul response to glucose, shows this
- this experiment can be used as a base for evidence in horses, due to the ethical restrictions on conducting a similar experiment on horses themselves.
REFERENCE: Bequet et al, 2001


How is serotonin synthesised in the brain?

Key components are:
Tryptophan, an amino acid in the general circulation
-- tryptophan hydroxylase
5 - hydroxytryptophan (5HTP)
-- amino acid decarboxylase
Serotonin (5-HT)
-- hydroxyindole methyltransferase
Melatonin (from the pineal gland)

Draw out the diagram don't be lazy!


What is the blood/brain barrier?

The BBB is a barrier that separates the brain from the general circulation. It only lets certain blood products into the brain. It is bathed in cerebrospinal fluid.


What is serotonin synthesised from?

It is synthesised from tryptophan, an amino acid.



Tryptophan is an amino acid that is able to cross the BBB. It is synthesised into serotonin.



Melatonin is a hormone that is produced from serotonin, but only during the hours of darkness. It acts as a depressant, the opposite of serotonin. Excess melatonin is produced when horses are kept in dark barns for long periods of time, which can cause depression.


What is a carrier protein? What is its role?

A carrier protein is a substance able to cross the blood brain barrier. It is involved in the synthesis of serotonin.
It acts as a bus, carrying products (such as tryptophan) from the general circulation into the brain - however, there are only a certain number of binding points (seats!).


What substances are allowed to cross the BBB?

Tryptophan and most amino acids, but only with the help of a carrier protein.


How is serotonin release affected with a high glycaemic response?

Tryptophan takes up more spaces on the carrier protein/bus and therefore more serotonin is released. Lots of insulin is released, which helps to store glucose, as well as neutral AAs. This storage of neutral AAs frees up more space on the carrier protein for tryptophan.


How is serotonin release affected with a low glycaemic response?

Lots of neutral AAs are taken on the carrier protein to the brain, leaving less space for tryptophan to reach the brain. Therefore, less serotonin is released. There is alos low insulin release.


How can the glycaemic response be managed?

- reduce the 'meal' dimension of feeding (feed little and often rather than two big meals). This may reduce abnormal behaviour linked with sudden serotonin release but may cause excitement/weaving at meal times.
- slow release systems, such as a feed ball
- change order of feeding --> grain given alone will cause a high glycaemic response, should be fed with forage



The nucleus accumbens is the part of the brain linked with hyperactivity. In humans it is activated by stimulants, such as cocaine or speed.
Low drug doses lead to a chilled, blissed out feeling, due to low levels of hippocampul stimulation
High drug doses lead to higher levels of hippocampul activity, to the point where the NA is stimulated


What can be a disadvantage of powder calming supplements?

The powder can be shaken and ingredients with different molecular weights will start to separate into strata. This will affect the dose and the effectiveness of the calmer.


What is the striatum?

The striatum is a part of the brain. It is located in the forebrain but is under control of structures in the midbrain (the substantia nigra and the ventral tegmental area)

It has 3 key parts:
- The nucleus accumbens
- The caudatus
- The putamen


Define the CAUDATUS

The caudatus is part of the striatum. It is linked with fine motor control. In humans, reduced caudatus function is linked with Parkinson's disease.


Define the PUTAMEN

The putamen is part of the striatum. It is linked with fine motor control.



Dopamine is a neurotransmitter. It is released from the substania nigra and the ventral tegmental area and binds to target in the striatum (NA, caudatus and the putamen)