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Communication

Introduction

Communicating with animals, in particular learning to understand the messages the animal is sending, is the most important part of diagnosis. Communication is a vital part of animal husbandry and the art of veterinary medicine and a very useful adjunct to the science of veterinary medicine. Before ordering a complete blood count and liver function tests, the astute clinician already will know that a dog is suffering from abdominal pain because it assumes an abnormal posture with rump high and head low, or that a horse that paces in its stall and kicks at its belly is suffering from colic.

Another important aspect of communication between veterinarian and patient or between handler and stock is assessment of an animal’s emotional state or temperament. Adequate restraint or, preferably, a quiet, tractable patient is necessary for thorough examination and diagnosis. Most practitioners learn eventually to recognize animals that will be aggressive or fearful and, therefore, require tranquilization, muzzling, or more stringent methods. It would be helpful for agriculture and veterinary students to learn in advance how to recognize animals’ moods. Learning by experience to recognize behavior problems may occur at the expense of a badly bitten hand or kicked leg. For their own safety, as well as for accuracy of diagnosis, clinicians should learn to listen to and watch for the messages their patients are transmitting both to them and to each other. Farmers can prevent injury to themselves and to their stock if they can interpret the animals’ messages.

Animals communicate not only by auditory signals, as humans do, but also by visual and olfactory signals. Many olfactory messages cannot be detected by humans, although male odors, such as those contained in the urine of tomcats and the very flesh of boars and billy goats, are quite discernible to humans. Goats and cattle can distinguish conspecifics by means of urine. Male urine is more easily distinguished than is female urine.138 We are all aware of vocal communication by animals, but many of these calls remain to be decoded. It is the visual signals made by ear, tail, mouth, and general posture that are of most benefit in gauging the temperament and the health of the patient.

Perception

Vision

Acuity

Communication in animals depends on their ability to perceive messages. The sensory abilities of domestic animals, with the exception of dogs and cats, have not been studied systematically. The perception of animals is almost always compared with that of humans. Dogs and cats have a higher critical flicker fusion (point at which a flickering light appears to be fused, or a steady light) than humans, which means that dogs and cats can see television, but in some cases the image may appear jerky to them.438 Cats respond to television, especially rapidly moving animations (mice, birds, or inanimate objects such as balls), and will spend 6% of their time watching the screen.634 Cats can discriminate illumination at one‐fifth the threshold of humans, but their resolving power is only one‐tenth that of humans.658 Cross‐eyed Siamese cats do not have stereoscopic vision; other cats do.1750 Environmental conditions affect visual acuity. Free‐ranging cats have been shown to be hypermetropic, whereas caged cats are myopic.225 The visual acuity of cattle, measured by using a closed or partially opened circle at various distances from the cow, is inferior to that of humans.639 Bulls have fairly poor vision; they are able to discriminate a 36 cm solid black disk from a similar disk with a white center, if the center is 1 cm or larger and the bull is within 1.5 m.1916 This indicates a visual acuity of only 23°, similar to the horse (23°) or the dog (10°).1588 Cattle have horizontally oriented pupils and, as a result, are better at discriminating vertical than horizontal details.2946 The visual acuity of sheep is between 11.7 and 14.0 cycles/degree. Chickens can perceive 7 cycles/degree.2812

In some studies, pigs have been found to have poorer visual acuity than cattle – a hundredth or a thousandth of a human’s. In the Snellen system, humans have 20/20 acuity, whereas horses have 20/30, dogs have 20/85, and cattle and pigs 20/200 acuity.2521 This means that what a person could see from 200 feet a bull would have to be within 20 feet to see. Cattle can discriminate objects at 2 lux of illumination. Cattle are also poorer in brightness discrimination compared to humans. They have a brightness discrimination threshold of 66 lux in bright light and 4.8 lux in dim light, whereas humans have discrimination thresholds of 105 and 4.2 lux.1810 Horses can see in dimmer conditions than humans; they can make visual discrimination at a level of light equivalent to the illumination in a dense forest on a moonless night.899 They can discriminate a difference of 14% in circle size, which is worse performance than humans. They use length rather than area to discriminate size. They pay more attention to local components than to global shapes, in contrast to humans.2273

Within‐Species Recognition

Sheep can recognize faces of other sheep and differentiate them on the basis of photographs. They can remember at least 25 different sheep faces for more than a year. Goats can discriminate familiar from strange goats, even if their horns are not visible.1189

Cattle can discriminate a photo of a cow from that of other ruminant species.460 They can recognize familiar cattle and learn to recognize unfamiliar ones, but have more difficulty learning to differentiate cattle of different coat patterns, especially all white cattle.461 When presented with photographs of cow heads, they are more likely to explore and lick the images of familiar cattle than unfamiliar ones, and they never lick a photograph of a pony. Heifers rewarded for choosing images of unfamiliar conspecifics pointed their ears backward more frequently (indicating confrontation with unfamiliar stimuli).461 In contrast, pigs do not appear able to discriminate between photographs of other pigs.819

Horses were more likely to approach photographs of horses displaying facial expressions associated with positive attention and relaxation, and to avoid stimuli displaying an expression associated with aggression. When presented with photographs of conspecifics, both horses and sheep identified emotional signals based on visual cues of changes in facial expressions.2984,2852

Chickens recognize breed differences, in that a rooster will attack members of a breed if another chicken of that breed was subordinate to him and avoid a chicken of a breed that was dominant to him.

We do not use one sense alone to identify individuals, and neither do animals. We recognize people by their voice and their appearance. Horses are also able to match the neigh of another horse with its picture.1865,1866 Dogs can be taught to differentiate dogs of various breeds from other animals.114

Cross‐Species Recognition

An important question is, “Can an animal tell the difference between different people?” The answer is definitely yes.2851,2864,3097 Areas that respond to human or dog faces, in particular the temporal cortex in the brain, have been located in dogs, pigs, and sheep.488,1196 Dogs and cats appear to interpret each other’s signals correctly even when the behaviors have opposite meanings in the two species, for example, tail wagging, which signals annoyance in cats and pleasure in dogs.688

Pigs can tell people apart, even if olfactory cues are masked, on the basis of visual cues such as height and facial appearance. They can even distinguish humans apart in dim (20 lux) light.1242 They can recognize familiar people and base their behavior on how that human treated them. Piglets will approach a stationary human even if that human has scared them, but will try to escape if that person or an unfamiliar person approaches them.

Cattle recognize people by their faces or the color of their coveralls, and use height to discriminate between people.1646,2012 Sheep are able to recognize human faces, but a photograph of a familiar stock person is not as effective as the stock person himself in calming an isolated lamb.2225

Dogs associate their owner’s voice with their face, and when a strange voice is played while the owner’s picture is displayed the dogs gaze longer, indicating that there is a mismatch. A dog can match a female voice by looking at a woman, but only if the dog lives with more than one person of each sex.1904 They cannot distinguish the smiling face from a blank face of a stranger of the opposite sex from the owner.1662 Dogs looked longer at faces when the voice being played at the same time matched the emotion of the face (i.e., angry voice – angry face).2645 Pupil sizes of dogs were significantly larger when viewing angry faces than happy faces.2989 D’Aniello et al.3102 reported that dogs are able to recognize human emotions from body odor because they displayed behaviors indicating stress only when being presented with human odor of fear.

When dogs were trained to lie still in an magnetic resonance imaging (MRI) device and were...