horse making snorting sound while galloping

Question
hello ma'am, why do horses snort while working at moderate pace early in the morning? i observed most of our indian racehorses snort while galloping at moderate pace around 6am or 6:10am. may i know why? does the horse has breathing problem? or does it mean the horse is enjoyed being ridden by the rider and hence making this snorting sound. i have attached a small length youtube link. please watch it and tell me!!
please dont tell that this is out of your expertise!!

http://www.youtube.com/watch?v=vqFnlmXcTNc

Answer
When horses gallop, the motions of their bodies causes their diaphragms to move back and forth in a rhythmic manner.

The diaphragm is the partition of muscles netween the chest cavity and the abdominal cavity. When the diaphragm contracts, it partially descends into the abdominal cavity , thus decreasing the pressure within the chest and drawing air into the lungs. (inspiration).When the diaphragm relaxes, it slowly reenters the thoracic cavity,thus increasing the pressure within the chest.As the pressure increases, air leaves the lungs. (expiration).The intercostal muscles between the ribs assist the disphragm in changing the volume of the thoracic cavity by elevating and lowering the rib cage.

The "blowing' sound you hear when the horses are galloping is indeed caused by the galloping movement itself.....it forces the air in and out of the horse's lungs because of the movement of the diaphragm under such movememnt. It actually aids the horse in getting enough air for the extreme stress of galloping.

Unfortunately, it is not all that uncommon for unethical horse trainers to give horses drugs...
as this strain can be hurtful to the horse, causing bleeding into the lungs, etc.