"She knows what she sees. She has her eyes in the right place." Though she was talking about a human, Swiss novelist Johanna Spyri could have been talking about a cow in the book Heidi. After all, being a prey animal, a cow must have its eyes in the right place, and in the bovine's case, that's on the sides of its head for an almost 360-degree view.
How cattle see
Prey animals, such as cattle, have horizontal pupils, unlike the round eyes of predators. They don't see up or down, they get a broad picture because their eyes are on the sides of their heads. "If you combine eye location and the pupil shape, it's absolutely magic," says Tom Noffsinger, DVM,
"This doesn't make sense to me, given the wide set of their eyes," comments Gavin Meerdink, DVM, Veterinary Diagnostic Investigations, Inc., Mahomet, Ill. "But when you drive machinery through a herd, cattle do give you the impression that they don't realize how close the tractor is until it nearly touches them. This seems universal, regardless of the familiarity of the animals with machines."
Meerdink explains that most veterinary students are taught that ruminants have a natural astigmatism, more near-sighted at the lower portion of their visual spectrum and more far-sighted at the top. "This makes sense, given the need to see what they are eating at the same time noticing the predator in the distance. Also, it seems that when they really want to examine something close, they will look off the end of their nose, an act that seems more obvious in horses."
Cattle probably don't have to move their head much to reach near 360 degrees "unless you're right and tight behind them," says Meerdink. "In other words, you won't sneak up behind a kicker without getting hurt out of the adventure if she really wants you."
Vision and cattle handling
Watching the bovine's movement can also give you clues as to what cattle are trying to understand. "A lot of time when cattle put their heads up and down, such as when they are being worked, they are trying to focus," adds Lynn Locatelli, DVM,
"Because of the way cattle and horses see, they hate a linear approach," notes Noffsinger. "The flight zone for cattle is not round, it's egg-shaped. In order for them to tell how far away you are, they have to move their head. To be respectful to a prey animal, you never approach it linearly."
Noffsinger, who works with beef clients on quiet and controlled cattle handling, says when cattle see where they can go, they are much more prone to move than if they can't see. "Cattle also like to go back where they entered, so we can use these ideas to improve handling. Taking away their visual abilities stops flow. If you walk toward them, they will tend to shoot past you in the opposite direction."
"Understand that when cattle raise and lower their heads they are undergoing visual adaptation," says Locatelli. This understanding facilitates moving cattle through processing facilities successfully. When the handler understands this, they know when to ask the animal to move forward so that the animal moves forward instead of backward.
"Handlers that create movement instead of standing completely still help the animals to understand that the handler is not a predator," adds Locatelli. "This movement gives the animal a point of focus -- the handler essentially wants to be seen and identified."
Cattle-handling expert Bud Williams explains that cattle want to see what is pressuring them. They want to move in the direction they are headed, so it makes no sense to drive them from behind in their blind spot when they will want to turn around to see you (visit www.stockmanship.com for more information on cattle handling).
Bad eyes in dairy bulls may be overlooked by staff not wanting to handle bulls.
Vision is important for other things than predator detection. Michael Overton, DVM, MPVM, University of California-Davis, notes that good vision is extremely important for dairy bulls, for example (Bovine Veterinarian, January 2005). Bulls often identify cows in estrus by locating the small groups of sexually active, riding cows that are often located away from the other cows. In a dry lot or pasture dairy, bulls must be able to see these cows to improve the odds of actually servicing and impregnating them.
One of the most common eye conditions is pinkeye. Sam Leadley, PhD, Attica Veterinary Associates,
Leadley says most of those clients also don't vaccinate for pinkeye. On better-managed dairies with a pinkeye vaccination program, they are encouraged to vaccinate young heifers right after corn planting and first cutting of hay (early June) and a give them a second injection about three weeks later.
Leadley notes that on high-treatment farms, diagnosis of eye problems are not usually done on a timely basis. "They fail to pick up tearing and/or discolored eyes at a stage of infection when treatment is most effective and before there is permanent damage to the eyes. It's pretty frustrating for veterinarians when the producer fails to provide care until there are ulcerated eyes that he or she is expected to ‘fix.""
Lynn Locatelli, DVM, says that when cattle raise and lower their heads they are undergoing visual adaptation and it helps them to focus on an object.
Though Leadley hasn't seen any data comparing growth or feed conversion rates for pinkeye-infected versus non-infected heifers, he believes the infection can take its toll. "Calves don't consume their normal dry matter, immune system demands on energy and protein are elevated and immune competence is lowered, making these heifers more prone to secondary infections such as respiratory illness."
Overton notes that dairy bulls encounter the same types of problems as cows do, such as pinkeye, but eye problems in dairy bulls can often get overlooked until they become severe. "Dairy workers tend to tiptoe around bulls from a safety perspective and aren't always comfortable handling or treating them," says Overton.
Jessica Laurin, DVM,
On the feedlot side, injury to the eye is the most commonly diagnosed disease in the
Generally, it is related to a foreign body, such as feed particles, blowing into the eye and the wind swirling them around the bunk. Many, if not most, feedlots ignore eyes until they are severe, he says.
"At MARC, we encourage the removal of cattle with watery eyes early to the hospital for examination and treatment if indicated," says
Anaplasmosis can cause anemia, which appears as severe paleness of the conjunctival mucous membranes around the eye. Photo by Jerry Vestweber, DVM
If an animal's eye hurts, it affects performance,
Eyes as diagnostic tools
"An animal's eyes have the power to speak a great language," wrote philosopher Martin Buber. The eyes may be windows to the soul in a poetic sense, but they can also be a window into diagnosing illness in cattle. "The eye is the window to the brain," says Meer-dink. "The first thing you hear from the owner is, ‘She seems a little dull in the eye."" Other messages he says the bovine's eye conveys are: "Where's the food," "I'm very excitable/irritable right now," "I don't feel good," "I am receiving no impulses from the outside world," and "I would like to die now."
Conditions such as dehydration can often be detected around the eyes. "Dehydration is evident in the eye but also in the skin and subcutaneously," says
Infections such as Salmonella can cause scleral injection in the eyes from damage to the lining of the blood vessels. Scleral vessels become large, engorged and can leak. Anaplasmosis can cause anemia, which appears as severe paleness of the conjunctival mucous membranes around the eye. Septicemia, especially in calves, can appear as cloudiness (hypopyon) in the eyes due to pus and white cells settling into the bottom half of the anterior chamber of the eye, between the iris and the cornea.
After an animal has died, the cornea can also give you some idea about how long an animal has been dead. "You can note the iris constriction," says
Toxic problems can often be diagnosed using eye fluid. "We have analyzed ocular fluid for nitrate/nitrite toxicoses, calcium and magnesium, and ammonia (urea toxicosis)," says diagnostic toxicologist Michael Carlson, PhD, University of Nebraska Veterinary Diagnostic Center. "The retina may be analyzed for cholinesterase activity as an indication of OP/carbamate toxicoses. (See "Submitting the eye for toxicology" sidebar.)
Septicemia, especially in calves, can appear as cloudiness (hypopyon) in the eyes due to pus and white cells settling into the bottom half of the anterior chamber of the eye, between the iris and the cornea. Photo by Tom Kasari, DVM
Cancer eye, or ocular neoplasia, is a condemnable condition at the slaughter plant and is one of the top 10 causes of carcass condemnation (see sidebar). Unfortunately, many times these cattle are ignored, despite the fact that early detection and removal of the tumor or eye can often be successful.
Years ago when Meerdink was in practice, he tried a beta radiation source -- on the end of a stem -- for treatment of cancer eye. He anesthetized the eye and held the radiation probe on the cornea for X number of minutes. "It worked if the neoplasm was small," he says. "But it took multiple treatments, and we had to start with an almost unnoticeable neoplasm. And, the radiation issue quickly made it unobtainable." Meerdink now suggests eye removal. "It saves the cow, and as an adult within the herd, one eye seems to be of no detriment."
"Older cattle with cancer eye should be examined by a veterinarian as soon as possible, and if a cure cannot be obtained, it should be euthanized at such point the disease progresses to cause the animal to suffer," says
Meerdink figures that the "line in the sand" with ocular neoplasia is whether or not the neoplasm has metastasized; in other words, is removal of the eye the end of it? "It's tough to diagnose, but when invasion beyond the globe into surrounding structures is evident, it's over," he says.
Seeing eye to eye
"A cat will look down to a man. A dog will look up to a man. But a pig will look you straight in the eye and see his equal," wrote Winston Churchill. It's not clear from this quote how Churchill would have seen the cow, but at this point, we may better understand how a cow might see him.
Specifics of vision
"No object is mysterious. The mystery is your eye," wrote Irish author Elizabeth Bowen. The bovine eye may be mysterious, but it's quite simple what it was designed for, and that's predator detection.
With their eyes positioned on the side of the head, cattle have panoramic vision of 330' and binocular vision of 25'–50,' which allows for good predator awareness (Phillips, 1993). Despite the wide set of their eyes, however, they do have a blind spot directly behind them (see right).
Cattle have slit-shaped pupils (Smith, 1998) and weak eye muscles, which inhibits their ability to focus quickly on objects (Coulter et al, 1993). Cattle can distinguish long wave-length colors (yellow, orange and red) much better than the shorter wavelengths (blue, grey and green), which may have aided their response and survival when a herd member was attacked and blood was spilled (Phillips, 1993).
Cattle can distinguish all colors from a grey background except blue (Dabrowska et al, 1981) and have a poor depth perception. Because of this poor depth perception and lack of definition, cattle will often balk and refuse to cross a shadow or drain grate and are best moved through diffuse light.
Excerpted from Blackshaw, JK: Notes on some topics in applied animal behaviour, ed 3, 2002. Updated by Paul McGreevy, BVSc, PhD,
Submitting the eye for toxicology
You can fix a lot of bovine tissues to send to the diagnostic lab, but diagnostic toxicologist Michael Carlson, PhD, suggests you don't fix the eye for toxicology in the traditional sense. Instead, remove the eyeball and keep it chilled; freezing it is probably not the best thing to do for cholinesterase activity. It is more convenient for the receiving lab if the eyelid and tissue surrounding the eyeball is removed.
"I tell my customers to ship the intact eye to me and I will harvest the fluid or retina, but if they want to harvest the fluid and ship it, they may do so."
Carlson describes how to harvest ocular fluids below:
1. Try to get aqueous humor first, then vitreous if no aqueous humor is obtained, using an 18-gauge x 1-in. or 1.5-in. hypodermic needle and a 5mL or 10mL syringe. Enter the anterior chamber by piercing the eye at the junction of the sclera and cornea with the needle bevel up away from the eyeball. Enter the chamber with gentle pressure. You should be able to see the needle in the anterior chamber through the cornea.
2. Rotate the needle about 90 degrees and aspirate the fluid by gently pulling up on the plunger of the syringe. If no aqueous humor is obtained, gently move the needle in the anterior chamber and continue to pull gently on the plunger to aspirate the fluid. If no fluid is obtained, then let off the plunger and enter the posterior chamber through the iris.
3. Once in the chamber, pull back on the plunger while moving the needle up and down within the chamber. If fluid is present in the chamber, it may take several "ups and downs" to find and aspirate it. Adult bovine eyes may contain up to about 1.5mL of aqueous humor and 5+mL of vitreous humor. Smaller eyes will yield smaller volumes of each humor.
To harvest fluid, Carlson doesn't even remove the eyeball from the plastic bag it comes in. "I force the eyeball to a corner of the bag with the cornea up against the side of the bag, and pierce through the plastic bag at the junction of the sclera and cornea as described above.
If the eye must be removed from the bag, it is more easily handled if it is placed in a paper towel or laboratory wipe. "The eyes are usually wet and slick when held with a gloved hand," he notes. "The towel or wipe helps with the grip. Make certain that you grasp the eye with the cornea away from the towel or wipe. They tend to stick to the towel, so rotating them after you grasp them with the towel is usually difficult."
4. The vitreous humor of some eyes, especially fetal eyes, may be very gelatinous and not aspirate into the syringe. If no vitreous humor is obtained as described above, or very little, then pull out the needle and place the syringe with the needle still on it aside. Cut across the cornea and into the sclera using a scissors, starting at the puncture hole made by the needle. Cut with the cornea of the eye downward over a container to catch fluid that escapes as the cornea is cut.
"We use a plastic weigh boat that is about 10 cm in diameter to catch the eye content," says Carlson. Gently squeeze out the contents of the eyeball through the incision into the container. The lens usually is intact and gelatinous vitreous humor is present.
5. Set what remains of the eyeball aside. Pick up the container and tip it so the contents move up against the side of the container. Aspirate fluid from around the solid or gelatinous mass into the syringe through the needle. The fluid may be black, which is usually because it contains parts of the iris in it.
6. Remove the needle and dispose of it properly and safely. Push the harvested fluid into a sealable vial. The specimen should be stored at 4'C if it will be analyzed within about 24 hours. If not, freeze it. The fluid may be centrifuged (~1,500 rpm for 15 minutes) before analysis to separate the fluid from solids that may have been aspirated with it. "We usually do not centrifuge it before freezing," says Carlson.
Send in the intact eyeball to the lab that is going to analyze the cholinesterase activity of retina. "The retina is fragile and best harvested right before analysis, in my opinion," Carlson adds.
Common eye diseases of cattle
What follows are some of the most common eye diseases of cattle.
Pinkeye (infectious keratoconjunctivitis): Although sporadic cases of eye diseases occur in all seasons of the year, this highly contagious, bacterial disease is most common during the summer months. Sudden onset begins with excessive flow of tears, holding the eye partially closed, rubbing the eye and seeking shaded areas. An ulcer develops within a short time in the central area of the cornea. An opaque ring develops around the ulcer, and within 48 hours of onset, the entire cornea becomes cloudy. The infection may affect one or both eyes. The lining of the eyelids becomes red with mucus and pus. As the ulcer deepens and extends completely through the cornea, the eye ruptures with loss of fluid and collapse of the eyeball. Immediate treatment and isolation of infected cattle are essential to recovery and in prevention of spread to other cattle.
IBR virus eye (infectious bovine rhinotracheitis): Upper respiratory infections are caused by the aerosol transmission of this virus that spreads rapidly through the herd and is most prevalent in the fall and winter. In the early acute stage, few cattle may develop cloudy cornea similar to pinkeye. The opacity spreads inward from the outer edge of the cornea, and there is no ulceration. Control measures include isolation of affected animals and vaccination of the whole herd and purchased replacements.
Cancer eye (squamous cell carcinoma): The frequency of cancer, like smooth plaques on the eyeball and ulcer or horn lesions on the eyelids, is increased in cattle without pigment in the eye and with constant exposure to bright sunlight. Excessive flow of tears occurs as in cases of pinkeye. Cancerous growths develop on the third, upper and lower eyelids and eyeball and spread to internal lymph nodes and organs. Recognizing the gross appearance of the lesions associated with the eye makes diagnosis of this cancer. Early detection is necessary for heating or freezing therapies or surgical removal of the tumor alone. In chronic cases with more extensive involvement, the entire eyeball and eyelids must be removed.
Photo eye (photosensitization): This noninfectious condition is a hypersensitivity to sunlight after ingestion of various plants or administration of certain drugs. In addition to cloudiness of the cornea of eyes, non-pigmented eyelids and nose, teats and vulva and areas of head, body and legs are commonly sunburned. Prolonged exposure of affected cattle to sunlight will cause blindness and severe skin damage. Sheltering during the day with grazing on pasture at night must be provided for protection from sunlight until the eyes and skin have healed.
This information was excerpted from Buddy Faries,