|Equine Physical Examination
Watch the horse closely as you approach as you can obtain a lot of information from a cursory visual exam - attitude, overall weight and conditioning, ambulation, posture, etc. A healthy horse is usually interested in new people, will come over to investigate and often sniff you before allowing you to touch him or her. Normal temperature is 99.5-100.5 degrees F.
The haircoat should be slick and shiny and a length appropriate to the age and time of year. Look for areas of hair loss, matted hair, "scurf" or dandruff. Note the presence and number of scars, lumps or bumps. This may give you some insight into the lifestyle and/or environment of the horse. Common areas to find lesions are the ventral midline, just cranial to the udder or prepuce, in the mane, at the tail head, on the back of the pasterns, and in areas where tack is worn. Note areas with white hairs, these may be indicative of areas of trauma or other lesions.
Horses have large eyes positioned on either side of the head - this provides the horse with binocular vision, which means that the horse can see with either eye. The lateral positioning of the eyes and the horizontal orientation of the pupil gives the horse an amazing field of peripheral vision to almost 360 degrees. This means that a horse can see behind himself without hardly moving the head. The colored part of the eye, the iris, is usually brown. A few horses have blue or blue/white irises. Several small dark brown to black masses are usually located at the upper edge of the iris. These are called the "corpora nigra" and are normal. The cornea is the clear outer layer of the eye. It should always be clear. When damaged, it will develop edema and turn white. The conjunctiva are the inner linings of the eyelids and the outer layer over the white area of the eye, the sclera. Irritation of the conjuntiva will result in swelling, redness, increased vascularity on the sclera, and discharge from the eye. Vision is evaluated by observing the horse - does he notice things around him, does he bump into things. The "menace" response involves waving a hand at the eye - the horse should blink if vision is functional. The response of the pupils to light is also evaluated if vision is suspect.
Normal heart rate is 28-50 beats per minute. The horse has a 4 chambered heart as do all mammals. However, the equine heart rate is slow compared to humans and small animals - ranging from 28 to 48 beats per minute in the resting state. Four heart sounds can sometimes be heard in the horse, due to the heart's large size. S1 and S2 are always heard and are often described as "LUB-DUB", with greater intensity to the second sound. Heart sounds are actually due to movement of blood through vessels or vibration of the valves or heart muscle at specific times during the cardiac cycle. The normal rhythm of a horse's heart can actually be somewhat irregular due to physiologic arrhythmias that occur at slow heart rates, especially in fit horses. Murmurs may sometimes be heard - these are associated with turbulent flow of blood through vessels and heart valves. Quiet murmurs that are present but not easily heard are usually considered normal, again associated with the large size of the equine heart - one can sometimes hear blood moving through it.
The neurologic system is divided into central and peripheral areas - the brain and spinal cord make up the Central Nervous System (CNS). There are 12 cranial nerves that originate in the brainstem to innervate the organs of sight, smell, and hearing, the muscles of swallowing and mastication, the tongue, sensation of the face, and use of the eye and facial muscles. Abnormalities of these nerves will produce changes in head carriage, balance, eye position, ear and eyelid tone and position, vision, smell, hearing, and problems prehending, chewing, and swallowing food. The 10th cranial nerve, the vagus nerve, also affects cardiac function, respiratory function, and GI motility. Numerous pairs of nerves originate from the spinal cord to innervate the rest of the body - muscles, ligaments, organs, etc. A neurologic examination includes evaluation of the central and peripheral systems. Changes in the functions mentioned above will reveal cranial nerve abnormalities. The peripheral and central systems are also tested by evaluating the horse's posture, gait, and his ability to control his limbs. The patient is observed closely in different circumstances - circling, stepping over obstacles, up and down hills, sometimes with a blindfold. Proprioception, the knowledge of where the limbs are in space, an important aspect of neurologic control, is also evaluated at the same time.
Since horses are prey animals in the wild, they are designed to be able to run away at high speed. Accordingly, they have very large and highly efficient lungs compared to other species. The caudal border of the chest cavity can be found along a line drawn through the following points - the 6th rib at the elbow, the 11th rib at the costochondral junction, and the 16th rib at the transverse processes of the vertebrae. Airway sounds are most easily heard over the major bronchi, which should be located on the chest just above and behind the elbow. Movement of air through the small airways is usually not auscultable in the resting horse. A "rebreathing" examination can be done to make the horse breathe deeply. A plastic trash bag is held over the nose with enough air inside for several breaths. The horse breathes the same air in and out. This causes the carbon dioxide level to increase, which makes the horse breathe deeper and deeper. Movement of air can then be heard in the periphery of the lung. When the bag is first removed the horse will take a couple of very deep breaths - this is a good time to listen also. The horse's ability to tolerate this exam is also important - horses with respiratory disease may become uncomfortable, cough, and take a long time to recover after the bag is removed. Abnormalities can be heard as "wheezes" or "crackles", when airways are narrowed or obstructed by exudate. Normal respiratory rate is 6-16 breaths per minute.
GI sounds or "borborygmi" are associated with contractions of the intestine and should be present bilaterally, especially in the ventral quadrants. They can also be heard during auscultation of the chest. They sometimes sound like far away thunder, especially on the left, but may vary a lot - gurgles, squeaks, etc. On the right, the sounds can mimic water dropping into a well as fluid ingesta falls into the cecum on that side. Auscultation of GI sounds is subjective - the actual sounds themselves are not always as important as the presence or absence. They may even be heard without a stethoscope, especially at feeding time. Water intake, fecal output and consistency should be determined and monitored. Changes in these can provide advance notice or help avoid the incidence of colic. The teeth should be examined at least twice a year by a veterinarian.
"Lymph" is a special fluid that is part of the housekeeping system of the body. This system is designed to help "clean up" tissues in both normal and abnormal circumstances, help fight infection, and provide drainage, especially in peripheral areas such as limbs. Normally, few lymph nodes are palpable in the horse. The submandibular nodes between the sides of the lower jaw can be felt easily. The prefemoral and cervical lymph nodes may sometimes be felt with deep palpation but should not be obvious.
Muscle mass should be observed for symmetry and palpated for consistency. Posture and gait should also be evaluated as part of a general physical exam, as abnormalities of the musculoskeletal system frequently accompany neurologic disease, and occasionally other systems. Lameness is a frequent problem in horses and is evaluated using both passive and active examinations (i.e. standing examination involving palpation and flexion of joints and evaluation of the horse moving at different gaits, respectively).