Bovine biology series

Part - 25 Eyes

The (beautiful) eyes

I have something rather embarrassing to tell you. As I have gotten older, I have discovered that more readily I can share some mistakes publicly. This is one that I am not proud of.

I am recalling a new heifer, newly calved and thus needing to get into the milking parlor for the first time. Now as a rule, on your dairy and on ours, we routinely ran the heifers through the milking parlor a week or so before calving. Then at the first milking, milk let down was easier; the new cow was familiar with her surroundings, the smells and sounds and lighting and even me.

Well, this heifer had calved on another farm. So we brought her home in the horse trailer and unloaded her within the holding pen. Try as I could, she would not go up the ramp into the milking parlor, no matter what I tried. She got more frustrated as I did. Finally, I grabbed an old neckchain.

For many of us, neckchains used to be a common sight on dairy farms. They identified the cow as to a number. They were steel and the ring that held the number was pried open with a flat screwdriver. But as we know, when Modern Farm came out with numbered eartags, with very visible numbers and an applicator, and with the use of lockups stanchions, these plastic tags replaced neckchains.

But we always kept a few around.

At times like this. Except I used the chain as an implement, driving this wary heifer into the parlor. Anyone that has ever handled cattle knows moments like this, so I will not go into detail. Other than to say that during a fleeting moment, the end of the chain struck her right eye and it immediately collapsed the eye. She bled and bawled and went crazy. I stood in terror, as I thought, "what have I done?"

Well, I got some help and we got her into the parlor and we got her milked and she survived and so did I. But I learned two very valuable lessons that afternoon. Never, never take a chain to cow, and always, always go get help if an unwilling heifer will not go where I wish her to go by myself. Such lessons are learned on farms, and in this way, this twenty-year-old story introduces the topic for this month.....the beautiful eyes of a cow.

The eye is anatomically quite a complex organ. This should not surprise us, really, for the eye, in contrast to all other sense organs, is the one a cow sees her world from. What a remarkable organ this is, in that light can enter the eye, and with the nexus of the optic nerve, interpret this light as nerve stimuli, influencing learned images implanted upon the brain. At our first waking moment, or in the case of the calf, the eye is the organ through which the vastness of the world is discovered. With each passing day, the images accumulate and are etched into the brain tissue as remembered images. I assure you, at this very moment, twenty years later, I can sit her and so plainly remember the chain striking the eye socket of this heifer, and watching in horror the blood and eyeball fluid run down her face.

The eye consists of the eyeball or globe. In it is the aqueous (water) portion, bathing the iris, the lens, the suspensory ligaments that hold the lens in place, and the vitreous fluid behind the lens.

Picture this: The eye is a globe. From the top and from the bottom are ligaments, comprised of connective and muscular tissue. At the center of this globe, inside of it, these ligaments delicately hold the lens. You may think along the lines of a basketball, in that at the extreme poles of this ball, at opposite ends, there are these ligaments that suspend a lens at the center of the ball. In front of the lens is a moist fluid called the aqueous humor. Behind this lens is another bit of liquid substance called the vitreous humor.

What is the purpose of these fluids, in front of and behind the lens? Well, They bath the lens tissue in fluid, allowing it to float and flex and move about inside this globe. When a cow shakes her head rapidly, the lens can give a little. Another purpose of this fluid is to cushion the lens against shock. Obviously, the aqueous humor in front of the lens is transparent, for if it were not, vision would be several limited. One interesting note about this clear fluid is that it is cleaned and exchanged regularly, again, so that vision is not limited with cloudy aqueous humor.

The vitreous humor is also clear, is gel like, and is similar in chemical makeup as the aqueous humor except that it contains substances that keep the lens pushed towards the front of the eye, and the back of the eye, the retina, against the outside layers of the eye from which the optic nerve originate.

These are primary components of the inside. On the outside, of course, is the cornea. This is the part of the eye globe that is exposed to the environment. As such, it must have some interesting attributes. It must be clear so that light is easily passed through it so the lens may accept the full radiation of intensity of the light and image. It is devoid of blood vascularization too, so that blood itself does not interfere with incoming light. And the cornea must be bathed in fluid on the outside. Without thinking we blink our eyelids, thus washing the surface of the cornea with cleaning fluid. A cow does the same.

Two other anatomical words are familiar to us, the iris and the pupil. The iris is comprised of pigmented (colored) [oh, I must comment here....the color of a persons eyes, a very noticeable part of what we see in someone's face, is the color of the iris. I mention this because as a Nordic person, we fair-skinned people have blue eyes. Others of Mediterranean origin may possess brown eyes. In both cases, it is the color of the iris, which is described and makes the eye so beautiful]. The primary function of the iris is to expand and contract depending upon the intensity of the light coming into the eye. If the light is intense, the iris expands covering the lens, reducing the opening upon which light may enter the eye and strike the lens.

This opening, the black portion of the eye, is called the pupil. Thus the iris is like a curtain, moving back and forth in the aqueous humor fluid, changing the degree at which light can enter or strike the lens. As such, the iris is mainly muscle tissue, and is governed by the nervous system. The nerves interpret the intensity and radiance of the image; as a protective measure the iris moves tissue to let more light in or reduce the light, controlling the size, then, of the pupil.

At the back of the eye is the retina. It is here that light strikes after having been focused and concentrated by the lens. Here, there are cells called photoreceptors. As light strikes these photoreceptors, there are bodies in the retinal tissue called rods and cones that electrically interpret the image, a truly remarkable function of converting light energy into an electrical one.

Vitamin A is important in maintaining the retina so that the rods and cones may adapt to light and dark. A lack of Vitamin A can cause some or total night blindness.

We know that the function of the lens is to focus and concentrate the light so that it strikes the retina properly. Properly means correctly interpreting the light image so that the correct electrical signal can be sent via the optic nerve to the brain. That is why glasses are worn; the light is focused so that it enters the eye and then the lens properly, and therefore the light striking the retina in the back of the eye is correctly interpreted.

When I use the term electrical signal, I am referring nerve impulses. That is, the function of the retina is converting light energy into nerve impulses. This is facilitated by retinal pigments (again, related to the need for Vitamin A). Anyway, these nerve impulses are the end product of retinal function. As such, they travel via the optic nerve into the portion of the brain called the thalamus. The thalamus is a receptive center for sensory impulses, including those originating from the retina via the optic nerve.

So, this little ball of tissue through which the visual enters, first through the cornea, then through the aqueous humor fluid and controlled by the iris then focused through the lens, then the light image travels through the vitreous humor fluid then finally striking the retina. The light energy is changed into nerve impulses via chemical photoreceptors, and through the optic nerve, the electrical (nerve) impulse is presented to the thalamus portion of the brain. The thalamus, then, decides where to send other electrical stimuli, perhaps to muscles so the body can move, perhaps to the pleasure center of the brain releasing endorphins that make us feel good, or in the sake of a cow, to the pituitary gland so that oxytocin can be released in preparation for milking.....after the cow has entered the milking parlor and can see, visually, that this is a safe place, a familiar place, and one that she is not afraid of.

So these are the eyes. I rather believe them to be very beautiful, as if we can see into oneself. Cows are like this too, as we know that indeed, there are times when we can see the emotional side of cows by looking into their eyes.

Perhaps that is why I recall the heifer of some twenty years ago. In her, one eye remained, and frequently she looked at me.

I wonder what she thought?