Horse's Sense of smell
Since the size of nose causes a problem, it stands to reason that it must be important enough to be worth putting up with the inconvenience!
If it is hard to imagine the visual sense of the horse, then it is virtually impossible to imagine the wealth of information conveyed by its sense of smell. It has been calculated that, if you could spread out the sensory mucous membrane of the horse’s nasal cavity, it would be big enough to cover the entire animal’s body surface. Attempts have been made to assess how many times greater the horse’s sense of smell is than our own, with estimates ranging up to the hundreds of thousands. In all fairness, these estimates are nothing but guesses and the truth is we do not know for sure, (for instance the increase may be linear or exponential) but we can with complete safety and surety state that it is many, many, many, times greater.
(1) - Incisor; (2) - Nostril; (3) - Olfactory sensitive lining (many layers); (4)- Nerves from olfactory sensitive cells to brain; (5) - Olfactory lobe (6) - Celebral cortex; (7) - Hond brain; (8) - Brain cavity in skull; (9) - Lower jaw bone; (10) - Molars; (11) - Pre-molars; (12) - Touch sensitive whiskers.
The information provided by the horse’s sense of smell could be expected to be nothing short of fantastic, but the horse takes even this a stage further with its built-in scent analysing laboratory, The Organ of Jacobsen, (Vomeronasal organ). This is also present in some predators such as the lion, but not in people. It is believed that the Vomeronasal organ allows the horse to trap and analyse smells for the presence and identification of pheromones, which are chemical scent communication signals.
So what is the information which is received, and why should the horse have such a powerful equipment array when it already possesses such a refined visual sense?
One reason is that scent messages are able to travel over greater distances than is possible with line of sight and are able to provide information that is not possible to convey by sight. A scent message can be received when its owner has left the area - an "I was here" marker, and not only that but also "and this is who and what I am" as well as "I belong to this group".
If trained human perfumiers are able to identify 10,000 separate and distinct aromas, how many might the horse be able to distinguish?
We know that pheromones dictate the lives and behaviour of many insects and animals. These chemical messages contain information on sexual condition, fertility, readiness to mate and pregnancy, synchronicity of oestrous, state of mind, state of health, group identity, direction and distance.
When we wish to test a mare for pregnancy we test for various levels of chemicals in the blood, urine or faeces. We know that the foods we eat, and our emotional state, cause changes in the chemical content of our sweat. It makes perfect sense for the horse to have developed its sense of smell so as to be able to sense these changes, both in other members of the same species, and in the air around it.
An eater of meat, such as a predatory big cat, must smell strongly; indeed, were it not for this, why would certain predators attempt to mask their smell by rolling in the dung of animals which might be their prey? (You could be forgiven for wondering what our own diet makes us smell like to the horse). In the battle for survival between predator and prey we see a story of measure and counter-measure, neither succeeding in achieving ascendancy over the other in case the natural balance which allows both to survive be destroyed. Perhaps our safest and most intelligent approach to the Equine sense of smell is to set our imagination free and to allow that it may be so fantastic as to dwarf our own development of the sciences of medicine and physics, and that the horse could fairly consider us to suffer from a type of blindness with regard to the information carried in a single breath of air, which Equines, no doubt, take for granted.
The horse has practically unique and perfect olfactory memory. So the smell of the person which is many-many years ago looked after a horse, it will recollect in long years and recognize him by a smell.