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Have you ever stared deep into your horse's eyes and wondered what they really see besides a funny looking two-legged horse? Can they even appreciate the time and effort you put into picking out the color of a blanket? How do they tell the difference between a stick on the trail from a snake? In this article, color recognition, night vision, field of view and depth perception are discussed. Lastly, behavioral issues that are similar to vision loss are considered. The design and function of the equine eye has enhanced the horse's ability not only to survive in the wild, but also to work and perform in their domesticated settings. Their ability to see is not only dependent on a functional eye, but also on intact neural pathways and processing centers in the brain. The eye collects information about the outside world such as movement, size, color, distance, depth etc, but the brain is where this information is deciphered and reactions determined.
Color and day vision
The equine retina, like the human retina, uses cones to interpret light of different wavelengths. Light of differing wavelengths corresponds to different colors. The cones of the retina are only sensitive to certain wavelengths of light. Horses have two types of cones that are sensitive to wavelengths of light between 380nm-760nm. This corresponds to a color spectrum of blues, greens, and yellows with limited red. Cones work most effectively in bright light which emphasizes wavelengths in the yellow, green and red. The horse eye has the least amount of sensitivity to blue wavelengths in bright light. In dim light, the green and blue wavelengths are much more visible. The equine eye has mechanisms to improve vision in bright light. The pupil shape and specialized structure on the iris, the corpora nigra, limit light intensity and entry into the eye to prevent overstimulation of the retina. Additionally, the equine lens contains yellow pigments which filter out shorter (blue) wavelengths of light and reduce glare.
In low light conditions, the rods of the retina become primarily responsible for interpreting the visual world. These photoreceptors, unlike cones, are not color sensitive. This is why vision at night for humans seems more gray. Certainly horses have a greater ability to see in dim light than humans. Horses have evolved several adaptations to help with this. The horse has the largest eye of terrestrial animals, this allows a greater amount of light to be captured by the equine eye. The pupil is more elongate in a horizontal direction and can be dilated to six times that of a human. This change in pupil size allows tremendous capture and delivery of available light to the retina. Light is also processed differently in the equine eye as opposed to the human eye. Neural processing by the retinal bipolar and ganglion cells summate light signals and may actually make retinal images appear brighter. The eye of a horse continues to increase in sensitivity to light for longer than humans as they adjust to low light environments (up to 30 minutes) which heightens their ability to see. This may also result in the animal's hesitance to rapidly move between light and dark areas. The presence of a tapetum (reflective arrangement of collagen fibrils just under the retina) allows horses to see better in dim light.
Field of vision and depth perception
Given the location of the horse eye within the skull, horses can see from their hind limbs to their nose. Specifically they possess 350 of 360 degrees of visual field. Blind spots though do occur directly in front of the forehead, directly below the nose, and the base of their tail. The visual field of each eye overlaps in front of them allowing them to see the world in three dimensions. Humans are considered to have better depth perception than horses.
Behavioral disorders suspected to be related to sight
Spooking is a behavioral response of horses to a surprising or threatening stimulus. The stimulus at times has been associated with ocular disease processes. However, a common misconception exists that because of the positioning of the horse eye, horses cannot relate information about what they see with one eye to what they see with the other. This is untrue. Horses can see an object with one eye and process the information in the brain recognizing the same object when seen with the left eye. Abnormal behavior relating to head shaking or spooking may, however, be related to many different ocular abnormalities. The list of ophthalmic diseases responsible for vision deficits is exhaustive however some examples are corneal irregularities or deposits, iris cysts, cataract development, lens position abnormalities, vitreous degeneration, retinal degeneration, and uveitis. It is recommended to have your horse's eyes examined if vision related behavioral changes start developing. The equine eye is a fascinating structure which possesses adaptations and abilities unique to the horse. Disorders in the structure and function of the eye will commonly relate to certain behavioral changes. Understanding more about the equine eye helps us get closer to answering the question "What do they really see?"
If you have any questions regarding your horse's vision or any other equine medical issues, please contact your veterinarian or any of the veterinarians at New England Equine Medical & Surgical Center. Our ophthalmologist, Dr. Nicholas Cassotis, is available on Fridays for outpatient appointments and anytime for equine ocular emergencies.
Betsy Lordan, DVM
Nicholas Cassotis, DVM, DACVO
Jacqueline Bartol, DVM, DACVIM
Using Leg: A confusion of terms
By Nancy Wesolek-Sterrett
Dressage Department Head, Meredith Manor International Equestrian Centre
An online chat about an article that discussed how to get the horse ‘in front of the leg’ caught my attention recently. The students argued whether the writer was right or wrong. When I read the article, I realized that their disagreement arose, in part, because of the bewildering use of terminology in the horse industry. People use different terms to mean the same thing. Or they use the same term but with different shades of meaning. As an example, let’s take a look at hoW the meanings of ‘forward’ and ‘in front of the leg’ might get tangled.
The first thing a baby green horse learns about leg pressure is that if he moves forward when he feels pressure from both legs simultaneously, the rider releases the pressure and it goes away. That pressure may be described as a squeeze or a bump or a tap but they all mean ‘the lightest possible pressure the horse will understand.’ The release of that pressure is the horse’s reward. We are only looking for a directional response, not for a particular speed or a particular shape the horse takes with his body. Trainers call this basic understanding of leg ‘forward’ or ‘moving off the leg‘ or ‘forward off the leg’ or ‘respect for the leg’ or similar terms.
As the horse progresses from this very basic, baby green response to higher levels of training, the rider adds layers of sophisticated nuance until the horse understands the individual meaning of a wide range of leg pressures. But at every level of training, the basic response we expect when the rider applies pressure with both legs simultaneously is that the horse moves ‘forward’ immediately.
‘Going forward from the leg’ is a precursor to having a horse ‘in front of your leg. I feel this term confused the students in the chat room because it did not precisely describe the response from the horse that the writer intended. When talking about a horse being in front of the leg, I prefer to describe the rider’s feeling that the horse ‘moves forward into the hands’ or ‘moves forward into a connection’ with the rider’s hands. The rider closes the leg and the horse responds by pushing off from behind, lifting the back, rounding the neck and connecting to the rider’s hand, thereby completing the circle of aids.
Moving ‘forward into connection’ is a much more sophisticated forward response not to just leg but to a combination of legs, seat and hands than the green horse’s simple ‘respect for the leg.’ When I close my legs on a more advanced horse, I want him to do more than just go forward quickly. I want him to step well under himself and push off the ground energetically with his hindquarters, taking a particular shape with his body that transmits that energy into my hands holding the reins.
In the beginning stages, the combination of legs, seat, and hands feels like a mixed message to the horse. I am saying GO with my legs and HOLD YOUR FORWARD ENERGY A BIT with my seat. My goal is that when he feels this apparent contradiction, he will step farther under himself than he would have from leg pressure alone, contract his abdominal muscles to lift his back and withers, and allow an energetic connection with his driving hindquarters to flow up into my hands holding the reins.
Some riders try to ride their horses faster into ‘connection’. Adding more leg pressure without modifying it with seat and rein aids only asks the horse go forward faster. Forward is simply a direction, not a connection with the hands. Horses cannot go faster forward into collection nor can riders gather a horse’s forward energy into collection by pulling on the reins. Connection starts with that powerful thrust from the hindquarters that moves through the horse’s body in a way that allows the rider’s hands to gather and direct the energy.
Also adding to students’ chat room confusion, different riding systems describe different methods for applying leg—bump, tap, squeeze, flutter, pulse, use heavy leg, use light leg, lay leg against the horse’s side, keep the legs away from the horses’ sides, drive every stride, drive and leave the horse alone, and the list goes on. “How DO I use my leg?” lamented one chat participant.
There is, unfortunately, no simple formula that I or any other instructor can offer that fits every situation. How the rider applies leg or other ‘forward’ aids depends on multiple factors. Here I will discuss two of those factors:
* THE HORSE’S TRAINING LEVEL – In our training classes, students learn to first SHOW a horse what they want him to do. At the next stage, they can ASK for what they want. When the horse consistently gives what they ask, they can then TELL him what they want and expect a response. If the horse does not respond, only then is it fair to ENFORCE their request. The rider enforces forward movement with only as much pressure as needed to get a response. That might be increasing levels of leg pressure, a kick, or a touch of the whip added to leg pressure. Spurs, by the way, are not on the list of aids for forward movement. They are used to encourage hindquarter engagement (that first step in collection).
The rider starts with the least amount of leg pressure and increases the pressure until the horse moves forward. The rider pays attention to the horse’s response to the aid and changes the aid based on the horse’s feedback. The next ride, the rider does not start with a tap of whip pressure because that was what it took to get a forward response the last time. Then that would become the pressure that the horse understands as ‘forward.’ The goal is to help the horse respond respectfully to the least amount of leg pressure.
* THE HORSE’S TEMPERAMENT – Leg pressure must have meaning to the horse. It must be part of the vocabulary used by both horse and rider to communicate. The hot horse that needs no leg to move off as soon as the reins are released must learn to allow the rider to apply leg pressure. When a horse runs from leg pressure, he may be going forward but the rider cannot get that energetic connection from back to front. As training progresses, however, hugging lightly with the legs creates a corridor that helps this type of horse relax and trust the legs. At the other end of the spectrum is the placid horse that ignores a leg constantly bumping or gripping his sides. This horse is more likely to pay attention to a fluttering leg or a bumping leg against his sides. The horse would ignore a constant leg pressure and start going slower and slower.
When terminology confuses riders they should ask their trainer or riding instructor to explain how they are using a particular word or phrase. Good instructors know how to explain the same thing different ways to suit the learning styles of individual students. If riders come across the use of a term in an article or book that seems to contradict their own understanding of the term, they should search for the author’s definition or try to tweeze the meaning out of context. Different riding disciplines and different schools of training within individual disciplines often use the same or similar terms with different meanings. Don’t let it throw you. Just keep learning.
Do I have an emergency? A horse owner's guide to basic first aid
Most horse owners will experience some type of emergency with their horse at some point. Lacerations, colic, severe lameness, and other medical emergencies happen all too commonly with our animals. However, there are some steps that you can do on the farm and some information that you can give to your veterinarian to help guide the appropriate treatment and determine the urgency of the emergency.
Building a Basic First Aid Kit
There are some essential items for every horse owner to have on hand in case of injury or illness. Below is a list of essential items to have in a first aid kit, but it is not an exhaustive list for items that may be useful.
Physical Examination Instruments:
- Watch with a second hand
- Standing wraps (quilts and wraps) of appropriate size
- Roll cotton
- Gauze 4"x4" squares
- Non-adherent pads
- Vet wrap
Other Handy Items
- Surgical (betadine or chlorhexidine) scrub and solution
- Sterile saline
- Sharp bandage scissors
- Cups or containers
- Extra halters and lead ropes
- Duct tape
- Tape measure
There are certain medications that can also be handy to have on hand in case of an emergency. These may include phenylbutazone, flunixin meglumine (Banamine), or sedatives. However, these have to be obtained from a veterinarian. And always remember, don't give your horse any medications in an emergency situation without consulting with your veterinarian first and only use them under their guidance. Giving certain medications in emergency situations could make the horse's condition significantly worse or diagnostics difficult if given before veterinary consultation.
Performing a Physical Examination
Knowing how to perform a basic physical examination is a skill every horse owner should know. It is also important to know your horses' normal vital signs. Physical examination parameters have a wide range of normal values, and it is useful to compare vital signs in an emergency to your horses' known normal values. As a general rule, normal heart rates range from 32-44 bpm, respiratory rates between 8-16 bpm, and temperature between 99.5°-101.5°F.
To take your horse's heart rate, place your stethoscope just behind their elbow on the left side of their chest. You will hear a "lub-dub", which constitutes one heart beat. You can also feel their pulse to take a pulse rate. Feel under the round aspect of their jaw and you can find the round artery and vein. Place light pressure with your fingertips until you can feel a pulse.
To take your horse's respiratory rate, you can watch the rise and fall of their chest or abdominal wall with their breaths. In normal horses it may be a subtle movement. You could also place a piece of glass in front of their nostrils and watch it fog when they exhale, however some horses will snort at this and increase their respiratory rate.
To take your horse's temperature, stand to the side of their hindquarter. Gently lift their tail, and insert a lubed thermometer into their rectum. If you have a mercury thermometer, be sure to attach it to their tail with a clip and leave it for a full 2 minutes. Digital thermometers are quite quick and you can just hold it until it finishes. Make sure you stand in a safe position, as some horses will kick during this procedure.
Some other parameters that are good to look at include mucous membrane characteristics. To look at their mucous membranes, gently flip their upper lip to look at their gums. Normally their gums should be light pink and moist. In addition, you can check a capillary refill time (CRT), which is an indicator of vascular perfusion. To do this, press your thumb into their gum until the tissue underneath it blanches white. Then release the pressure and count how many seconds it takes for the pink color to return to the area. Normal CRT is less than 2 seconds. Gastrointestinal motility sounds (Gut sounds) are another parameter that is great to listen to, as it can vary significantly between horses and during different times of the day. The best way to learn what normal gut sounds are like is to listen to normal horses. This parameter is particularly useful in colic cases, where gut sounds may be increased or decreased. Lastly, digital pulses are a key parameter, particularly in laminitis or lameness cases. To palpate the digital artery, feel down near the horse's coronary band for a group of round structures on the outside of their limb. Palpate gently over this area to see whether you feel a pulse. It is common to not feel digital pulses in normal horses, but very strong pulses to their hooves can indicate a problem.
By performing a brief physical examination on your horse, you can provide important information to your veterinarian before they are able to reach the farm, and give some direction as to whether there are any treatments that can be initiated immediately. However, always be sure to contact a veterinarian before administering any medications or starting treatment.
Please contact your veterinarian or any of the veterinarians at New England Equine Medical & Surgical Center with questions regarding how to handle emergency situations or any other equine medical and health questions.
Erica J. Secor, DVM
Jacqueline M. Bartol, DVM, DACVIM
NH Trails in Jeopardy
Dear NH equestrians/tax payers:
Once again, people are trying to push horses out of the picture. There is an immediate need for us to speak up to protect our rights on state land including beaches and forests. Please take a few minutes to review these proposed changes that will affect us in a major way. If you think you'll have no problem taking a pitch fork and potato sack on trails, then no worries; you can stop reading now. However, most of you may find it difficult, and if you would like to continue to ride in state parks, then please send an email to voice your opinion or attend the meeting or one of the hearings. This affects the whole equine industry, and we have the right to speak up about it. Please remember to be polite when airing your concerns.
Proposed changes: CLICK HERE The underlined sections are the proposed new regulations.
There is a meeting scheduled on October 1, at 1 P.M. (conveniently at a time when most people are at work and cannot attend), at DRED's Large Conference Room, 172 Pembroke Rd, Concord, NH. If you can be there, please come. There are other public hearings -- go to the website for more info.
www.dred.state.nh.us‎ for a listing of the hearings –
Oct 1, 6 P.M. - Plymouth University, Plymouth;
Oct. 3 6 P.M.- Peterborough Town Library;
Oct 8, 6 P.M. - DRED Lancaster Office, Lancaster;
Oct 10, 6 P.M. - Hampton Beach Seashell Oceanfront Pavilion, Banquet Room, Hampton, NH
DENTAL CARE FOR GERIATRIC HORSES
I think we can all agree that geriatric horses (over 20 years) are more often than not an honored member of any barn. However, with advanced age they often possess teeth that are worn, irregular and even missing, which brings the need for extra special care.
A quick review of equine dental anatomy tells us that horses have a tooth growth pattern known as hypsodont, which means they are constantly growing (well, technically they are erupting), throughout their lifetime. As a result, later in life we find that some teeth have either worn improperly, or just fallen out.
What are some of the most common problems that may be found in a geriatric mouth?
Shallow, or cupped teeth - this can make proper mastication (chewing) difficult.
Missing teeth (step mouth) - watch for remaining fragments if fractured, hay packing in socket, or extra growth of the opposing tooth.
Wave mouth - condition in which, front to back, the upper teeth become shallow halfway back, and the bottom teeth rise up to meet them.
Loose teeth - teeth that are just hanging on, but only enough to be a nuisance.
Dental care in older horses should be approached with realistic expectations, and striking a balance between preservation of remaining tooth and maximum functionality. Keep in mind some general concepts:
More frequent care: an older horse’s mouth can change quickly, so it is recommended that they are examined every 6 months.
Oral exam: It is important that your veterinarian perform a full oral exam prior to working in the mouth. Each mouth is different and should be approached as such.
Individual tooth care: Many times the dental arcade in geriatric patients is very irregular. In this case each tooth is best worked on and sculpted as an individual, not as part of a row. Power tools usually perform this best.
Feeding plan: An individualized feeding plan should be made following the oral exam and dental work.
I would like to briefly address the idea of incisor reduction, which is a bit of a debate among equine dentists. The goal for filing incisors (front teeth) is to allow the molars and premolars to better meet up and grind. However, filing them too much can cause issues with the mastication of the cheek teeth. Make sure you are comfortable with the idea of having the incisors reduced before it is done.
Lastly, it is important to discuss how a geriatric horse should be fed. As we have learned, no two patients’ mouths are alike, so logically no two feeding programs are the same. Generally, with an older horse we look to feed for both safety and nutritional requirements:
- Safety: Older horses are often at risk for choke, especially when teeth are missing. Always make sure you are careful with long cut or coarse hay, as they may ball up and become lodged in your horse’s throat. Alternatives may be soaking the hay to soften it, or feeding short cut hay, alfalfa cubes, or just good old grass.
Nutritional requirements: It goes without saying that every horse should be fed to meet their nutritional, energy, and roughage requirements, which may be harder in geriatrics due to limited feeding options. Generally supplements such as senior feeds or grains serve the purpose well, but be sure to always consult with your veterinarian or a nutritionist prior to updating any feeding plan.
Geriatric horses should be celebrated, so don’t let dental issues spoil the party. Proper and frequent care can most often make even the worst of mouths both functional and comfortable. Careful care coupled with proper feeding can allow them to enjoy the golden years that they have worked so long for.
Michael Marshall, DVM
Touchstone Farm Open House 9/7
Touchstone Farm, in Temple, NH, is hosting a Fall Lesson Open House on Saturday, September 7 from 1 to 4 pm.
Visitors can take guided tours of the farm’s riding and carriage driving facilities. They can meet the friendly Touchstone Farm horses, including Gruffy the 18-hand Clydesdale. Instructors Cris Sullivan and Andi Snow will conduct brief demonstration riding lessons and be available to chat with students and enroll them in lessons.
Carriage driving instructors and instructors from the farm’s Horse Power Therapeutic Horsemanship programs will also be on hand to talk about lessons in these programs.
The Touchstone Farm volunteer manager will be there to answer questions about the many kinds of volunteers needed at the farm. In addition, light refreshments and pony rides for children will be offered through the afternoon.
Touchstone Farm, home of Horse Power and Pony Farm, is a non-profit educational and therapeutic organization that fosters a community of belonging for people of all ages, abilities and backgrounds. Touchstone Farm offers a rich and challenging variety of experiences, which includes summer camps, able-bodied and therapeutic horseback riding and carriage driving lessons, an instructor training school, and equine-related specialty weekends. Grounded in a sense of place, mutual respect and well- being, the 28-acre farm is a sanctuary that nurtures connections, cooperation, self-confidence, and personal growth.