Normal Canine Behavior and Ontogeny: Neurological and Social Development, Signaling, and Normal Canine Behaviors

Chapter 4

Normal Canine Behavior and Ontogeny

Neurological and Social Development, Signaling, and Normal Canine Behaviors

Overview of Normal Dog Behavior

Why Domestic Dogs Are Special

Dogs have a relationship with humans unlike that of any other “domestic” animal. Dogs have been selected over time for true collaborative work with humans, and such selection has historically resulted in dog breeds and the attendant groupings, regardless of which organization defines the groupings (e.g., American Kennel Club [AKC], Federation Cynologique Internationale [FCI]).

Molecular data support that dogs separated from wolves 15,000 to 135,000 years ago (Cadieu et al., 2009; Leonard et al., 2002; Lindblad-Toh et al., 2008; Pang et al., 2009; Parker et al., 2004; Savolainen et al., 2002; Sutter et al., 2004; Vila et al., 1997; Vonholdt et al., 2010). Molecular and anthropological data support that dogs of different morphologies who were likely engaged in different tasks have lived together with humans for at least 15,000 years (Boyko et al., 2009; Castroviejo-Fisher et al., 2011; Morey, 1994; Pang et al., 2009). Stand-alone anthropological evidence supports that dogs have lived intimately with humans for at least 30,000 years (Bienvenido et al., 2009; Derr, 2012; Germonpré et al., 2009, 2012; Ovodov et al., 2011). For the past 3500 years or more (consider dogs portrayed in ancient Chinese and Egyptian art), there have been well-defined breed clusters or groups comprising dogs of different shapes and sizes who engaged in related tasks.

Regardless of the debate over timing, we should appreciate that one of the forces associated with speciation may have been a special, collaborative working relationship with humans that ultimately resulted in morphological variation in dogs as a relatively—perhaps profoundly—late development in the human × dog relationship. We accept that humans have changed dogs. We seldom consider the extent to which dogs may have changed humans. Our unique relationship with dogs may be due to convergent evolution of canid and human social systems that was the result of like groups meeting and recognizing the power of collaborative efforts, followed by secondarily derived, homologous changes in brain function (Saetre et al., 2004) that have allowed modern humans and dogs to rely on each other.

Dogs, as a species separate from wolves, likely co-evolved with humans over thousands or tens of thousands of years, during which time they may not have been fully “domesticated.” “Domestication” may have occurred when we began to develop breed groups intended for specific tasks, which happened 3000 or more years ago. In contrast to wolves, who require handling by humans early in their ontogeny (beginning by at least 14 days of age) to minimize fear and reactivity to humans, most dogs can adapt to delays in handling and exposure, and their normal, innate sensitive periods are greatly expanded from those of wolves. When dogs cannot adapt or when they seem to have short sensitive periods, such patterns are indicative of pathology. In dogs, it is likely that this sensitive period expansion occurred concomitantly with changes in molecular and neurochemical function and gene expression (Saetre et al., 2004) that may represent some of the true outcomes of active “domestication.” In contrast to dogs, but similar to other non-domesticated species, cats have a relatively short and truncated sensitive period for exposure to humans, which may be associated with or evidence of lack of tampering associated with “domestication.”

Both humans and canids live in extended family groups, provide extensive parental care, share care of young with both related and non-related group members, give birth to altricial (completely dependent, immature) young that require large amounts of early care and sustained amounts of later social interaction, nurse for an extended period before weaning to semi-solid food (dogs do this by regurgitation; humans use baby food, but the concept is the same), have extensive vocal and non-vocal communication (it has been estimated that 80% of all human communication is nonverbal) (Smith, 1965, 1977), and have a sexual maturity that precedes social maturity. These shared characteristics may have allowed dogs and humans to recognize similarity in each other that allowed exchange of information and that led to later “domestication” and changes on the parts of both dogs and humans related to task management.

Behavioral Ontogeny in Dogs

Early Brain and Behavioral Development in Dogs

Myelination of cranial nerves V (trigeminal), VII (facial), and VIII (vestibulocochlear/auditory) is present at birth. These nerves are associated with essential functions of eating, balance, and body-righting. As is true for other animals, myelin is almost completely absent from the brains of newborn puppies but appears during the first 4 weeks, at the same time ribonucleic acid (RNA) synthesis is increasing at a rapid rate (Fox, 1971). In humans, myelin is first deposited in the peripheral nervous system (PNS), the central nervous system (CNS) in the brainstem and cerebellum, and in components of some major motor systems just before and after birth. Myelination of the human brain cortices occurs well after birth and progresses over decades (Volpe, 2008). Dogs undergo a gradual increase in myelination of the spinal cord, motor and sensory roots, and efferent pathways starting at birth and progressing through 3 weeks, which is reflected in the development of olfactory, thermal, and tactile capability and in increased mobility associated with development of vision. PNS and CNS development is reflected in development of motor responses and reflexes in young pups. This period of gradual myelination is followed by more rapid myelination of the somatosensory cortex at about 4 weeks and a more even distribution of myelination of the visual and auditory cortex by 6 weeks (Fox, 1971). As with humans, myelination is slowest in the frontal lobe. As brain development progresses, canine behavior becomes more complex, and the markers for onset of “socialization” or sensitive periods appear to be neurodevelopmental.

Much of what is known about early social development is the result of work done by Scott et al. in a laboratory on five breeds of similarly shaped dogs (wire-haired terriers, Shetland sheepdogs, cocker spaniels, beagles, and basenjis), using a relatively small number of litters over 2 decades and observing pups beginning at 3 weeks of age (Scott and Fuller, 1965). These studies remain landmarks. We still lack comparable data on most breeds, yet such data could be relatively easily collected across breeds, as demonstrated by Schoon and Goth Berntsen (2011), who provide excellent data on neurodevelopmental landmarks from birth for 10 litters of Belgian malinois raised under controlled conditions.

The following broad conclusions appear to hold for most dogs:

• The “neonatal period” covers the period from birth to 13 days of age when puppies are dependent on rudimentary locomotor skills and use tactile signals to locate and orient toward dams and littermates. During this period, puppies vocalize if separated from their dams. Olfactory ability is present but poorly characterized in dogs this age. Few data about tactile signaling exist, yet given its early importance it should help structure brain development.

• The mild stress of daily and early handling is beneficial for puppies and allows them to cope better with later stresses (Selye, 1952). Excessive stress should be avoided because chronic, excess secretion of adrenocorticotropic hormone (ACTH) has been correlated with a decreased ability to learn.

• From days 13 to 20, puppies become more coordinated, open their eyes, and begin to startle to sound. The change in motor abilities coincides with eruption of teeth at approximately day 20 and with improved vision. This period is traditionally called the “transition period.”

• Tail-wagging behavior becomes apparent at the end of this 20-day period, and there is considerable variation across breeds in this development. No one has investigated the extent to which use of the tail in signaling may reflect an effect of neurodevelopment but this is an important question.

• If pups are exposed to passive observers beginning at 3 weeks of age, they will approach and explore the observer.

• If pups are not exposed to passive observers until 7 weeks of age, they must habituate to the observers before they approach and explore. This habituation took 2 days in the laboratory setting (Bacon and Stanley, 1963, 1970; Freedman et al., 1961; Love and Eisenberg, 1986; Scott and Fuller, 1965).

• Dogs isolated from humans through 20 weeks became fearful of humans (Agrawal et al., 1967) and had impaired learning ability (Melzack, 1968; Melzack and Scott, 1957; Thompson and Heron, 1954).

• Even if kept with their mothers, by 12 weeks of age, puppies chose to wander extensively, a finding that anyone who has raised puppies has witnessed.

• Pups that were kept in kennels beyond 14 weeks were very timid and demonstrated a lack of confidence in any circumstances other than the kennel. These dogs would not voluntarily leave the kennel and became truly phobic of anything novel (neophobia) (see Scott and Fuller, 1965, for summary data).

• Different breeds responded differently to various rewards and restraints and differently with respect to various social contexts (Plutchik, 1971), and these patterns were replicable.

Based on these data, the period from 3 to 12 weeks was called the “socialization period,” from which a number of context-specific developmental periods were identified as “socialization periods.” These periods became prescriptive with respect to types and extent of exposure that were thought to be required to produce “normal dogs.” Instead, such data are best viewed within the context of a “sensitive period” (Bateson, 1979), which implies risk assessment. There are environmental and genetic aspects of all behaviors (see Figures 3-3 and 3-4 accompanying discussions in Chapter 3), and some individuals may benefit from earlier exposure than others. If the opportunities are available, non-pathological dogs will expose themselves when they are able.

A concept of a sensitive period takes such variation into account and is best defined as period when animals can best benefit from exposure to certain stimuli, and if deprived of such exposure, there is an increased risk of developing problems attendant with the stimulus. In other words, when animals are neurodevelopmentally able to respond to stimuli, they will benefit from exposure, and if they lack exposure, they could develop behavioral problems associated with the omission (Bateson, 1979; Cairns et al., 1985). This does not mean that all exposure is equal, that all dogs are ready for all exposures at the same time, that you stop exposing the dog when the dog is out of the sensitive period, or that if exposed, no dogs will have problems.

Given what we know about sensitive periods, exposure, and neurodevelopment, we may wish to replace the concept of a “socialization period” with one that uses the concept of a sensitive period as the time when we should ensure that dogs have access to the relevant stimuli. When dogs are neurodevelopmentally able to respond to the stimuli, they will do so unless they are impeded. This approach also includes exposure to new environments, something that a technical definition of “socialization period” does not include.

We also should remember the role for cortical development in how a puppy learns to respond to different stimuli and understand that the time/developmental period of imposed change matters to the dog. A study comparing 70 adult dogs who as puppies had been separated from their dams and litters 30 to 40 days with 70 adult dogs who as puppies were not separated until after 8 weeks showed that early age of separation was a significant predictor for excessive barking, fearfulness on walks, reactivity to noises, toy possessiveness, food passiveness, and attention-seeking behavior. These dogs were also more at risk for destructive behavior than dogs who had been permitted to stay with their litter through 8 weeks (Pierantoni et al., 2011). Clearly, there are potential roles for both the hormonal effects of stress/distress and the developmental phase in these findings. Considering the enhanced risk of relinquishment, abandonment, and euthanasia for dogs with behavioral concerns, welfare and behavioral standards should mandate that puppies remain with their litters in the home of and with access to the dam through 8 weeks of age (Box 4-1).

Box 4-1   Case Against Very Early Puppyhood Adoption

• By 3 to 4 weeks of age, pups start to follow each other (Scott and Fuller, 1965).

• By 5 weeks of age, they rush at an opening as a group. The more activity there is at the opening, the more frenzied the puppies will become (Scott and Fuller, 1965).

• In both kennel and field situations, the strongest attachment to location and companions occurs at 6 to 7 weeks. If separated from either family members or the location where raised, puppies become severely destabilized (Elliot and Scott, 1961). This response can be mitigated if all littermates are exposed to a variety of fairly benign circumstances, both as an intact litter and in smaller groups early in life. Separation from each other or a place at 6 weeks of age causes recidivistic changes in the puppies’ behavioral development. These findings constitute one of the strongest arguments in favor of the abolition of puppy mills. They also provide insight into why so many puppies that are placed at a very young age develop or continue to have behavioral problems.

• Stress at 6 to 7 weeks affects the pups’ ability to learn about housetraining (see section on stress and learning in Chapter 2). Puppies begin to form substrate and location preferences for elimination by 8.5 weeks. This is the period when they first have sufficient cortical development to learn about substrates and choose to act on them, while also having sufficient physical and behavioral abilities to inhibit elimination. Dams have stimulated pups to urinate and defecate until about 3 weeks of age. From 3 to 7 or 8 weeks, puppies eliminate whenever necessary, with little regard to location. Few people understand that young pups cannot inhibit elimination, and so they resort to punishment (see client handout, “Protocol for Basic Manners Training and Housetraining for New Dogs and Puppies”).

• If breeders are willing to housetrain the puppy and encourage its independence by ensuring that the pups are exposed to novel people and environments, there may be no costs and sometimes some benefits to keeping the puppy longer than 8.5 weeks. The amount of time involved in exposure is often smaller than anticipated: Fuller (1967) noted that semi-isolated puppies avoided the pitfalls of restricted exposure in as little as two 20-minute periods a week.

• Puppies respond best to objects, such as leashes, between 5 and 9 weeks of age (Scott and Fuller, 1965). Breeders can help puppies by starting to fit them with head collars, harnesses, and leashes (see client handout, “Protocol for Choosing Collars, Head Collars, Harnesses, and Leads”).

• Puppies separated from the dam and litter at the time of weaning display up to 100 vocalizations per minute (Elliott and Scott, 1961). This argues that one should not concomitantly wean and place dogs.

• Hand-reared puppies explore novel stimuli more than kennel-reared puppies when evaluated at 8.5 weeks of age because this is the major stimulation available to them.

• Separation of pups from their mothers at 6 weeks of age had a negative effect on the physical condition, health, and weight of pups (Slabbert and Rasa, 1993).

• Pettijohn et al. (1977) provide data that indicate that toys have no effect on relieving separation distress, but that social stimuli do. Humans may be preferred to dogs for relief of the social exposure stress that occurs at 7 to 8 weeks of age, the time when dogs are developmentally able to explore and learn from people.

• Some breeds that have been developed for work in groups (e.g., hounds) when reared alone until 16 weeks of age lose the capacity for spontaneous play. Play can be elicited, but these dogs play differently from dogs who were able to associate with other dogs (Adler and Adler, 1977).

• In dogs from 47 different breeds studied from birth to 9 months of age, “socially deprived” dogs were antagonistic when greeted by humans and exhibited agonistic behavior in response to human approach, whereas dogs that had adequate “socialization” exhibited normal, friendly greetings and were well adapted in other social circumstances (Feddersen-Petersen, 1994).

• Adult dogs, who had been separated from their dam and litter from 30 to 40 days, experienced a greater incidence of excessive barking, fearfulness on walks, reactivity to noises, toy possessiveness, food passiveness, attention-seeking behavior, and destructive behavior than dogs who had been kept with their litter through 8 weeks (Pierantoni et al., 2011). This is some of the strongest evidence that dogs should neither be separated from their litters and the influence of the dam nor adopted into a new home before 8 weeks of age.

General guidelines for exposure based on the available data are found in Table 4-1.

Roles for Play

Play appears to be important in every species in which it has been studied. Although play has been thought to have numerous roles in behavioral development and maintenance from enhancing coordination and locomotor activity to encouraging problem-solving ability and enhancing cognition (Spinka et al., 2001), it may be especially effective in teaching animals how to make mistakes successfully and in established baselines for well-honed, broad, basic communication skills. This hypothesis is supported by data showing that dogs who received more playful interactions from their people were less fearful in new environments (Tóth et al., 2008).

In dyadic relationships of dogs participating in free play, sex of participants does not affect play, but age does: older dogs play more forcefully than younger dogs (Bauer and Smuts, 2007). Play and play signals also appear to modulate interactions between younger dogs and more forceful older dogs in dyadic play. Play signals given by younger dogs alter the course of more forceful interactions by older dogs (Bauer and Smuts, 2007), likely by making intentions more clear.

Dogs playing with other dogs play with toys differently than dogs playing with humans. When dogs play with humans, they are more interactive and less likely to continue to hold the toy (Rooney et al., 2001). Humans play with dogs using vocal, tactile, and visual/postural cues that can affect how dogs play. When humans display the lunge and bow aspects of the canine play bow, dogs increase play, and lunging increases play duration and frequency (Rooney et al., 2001). If the humans added vocal signals, play was enhanced. Effective human play with dogs enhances the relationship between the dog and the human, reduces the incidence of behavioral problems, and encourages humans to think that their dogs are very clever (Rooney and Bradshaw, 2002, 2003).

Play signals affect how dogs interpret the information provided by interactions between humans. In staged contests between humans, dogs whose humans give play signals approach more quickly than dogs whose humans provide no signaling information (Rooney and Bradshaw, 2002). Because play behavior involves a number of signaling modalities (vocal, visual, tactile, olfactory [licking, sniffing]), the redundant signals involved minimize the risk of mistakes in communication and help young animals learn about managing mistakes and quick changes in interactive behavior.

Early Exposure, Puppy Classes, and Vaccination Programs

Dogs should be allowed sufficient safe access so that when they enter their individual sensitive periods, there is no impediment to them exploring the relevant environment or having the relevant social interactions. The earlier dogs can learn about the broad-scale social and physical environment in which they are to live, without inducing fear, the better. If dogs are protected from stimuli, they may react inappropriately when exposed later (Scott, 1963; Bacon and Stanley, 1970).

If the pups had healthy dams, are healthy themselves, and are engaged in a modern vaccination program, they can be exposed to as many situations as possible. Of 24,000 guide dog puppies who began vaccination at 6 weeks of age and were re-vaccinated every third week through weeks 12 to 16, fewer than 6 pups (image of 1%) who were healthy during the vaccination series got sick (Appleby, 1993). If there are available puppy classes or puppy play groups, any pup physically and behaviorally able to participate should do so. If pups shy from these groups or classes and gentle continued exposure does not alleviate their response, they need help immediately.

Very early fear is a problem for pups. Historically, pups from lines of dogs genetically selected to show fearful behaviors show the behavioral and physiological effects of fear by 5 weeks (Murphree et al., 1967, 1969). Pups from lines of dogs commercially bred for research purposes show almost the same distribution of fearful behaviors at 5 weeks of age as do their dams and sires at 1.5 to 2 years (Overall et al., unpublished). Puppies who are shy, worried, or anxious throughout early veterinary visits are likely to exhibit the same behaviors as adults at 1.5 to 2 years of age (Godbout et al., 2007). Early intervention is essential for such dogs.

One study has suggested that there could be a beneficial effect of pheromonal analogue collars on one of a series of behaviors studied, early excitability in class, and hence on learning in puppy classes, based on owner surveys (Denenberg and Landsberg, 2008). Even if this effect were real—and the data, techniques, and analysis are problematic (Frank et al., 2010)—the magnitude of the effect appears mild, especially considering that it uses a tool (ranks of owner responses) that may exaggerate mild and/or rare outcomes. There are no data to suggest that pheromonal products are helpful for early fears, and so treatment with interventions whose mechanisms are known to work should not be delayed. Early intervention, often involving medication, is essential for these dogs so that they have a decent quality of life.

Claims have been made that some types of handling and stressors, including those discussed in early neural stimulation, protect dogs from effects of later stress (Battaglia, 2009). Only one study has evaluated early neural stimulation in a blinded, controlled, rigorous manner, and this study showed that it had no effect on the dogs chosen for the evaluation (Schoon and Goth Berntsen, 2011). However, as the authors note, the dogs tested were purpose-bred to become mine-detection dogs and already lived in an extremely enriched environment where they were intensely handled and interacted with daily as part of their routine protocol. This is exactly the environment in which you would expect not to see an effect because the control dogs are also highly, albeit slightly differently, stimulated. For dogs raised in homes, kennels, or commercial breeding facilities where dogs are behaviorally deprived, early stimulation of any kind is known to be beneficial.

Brain Changes and Social Maturity

The time between the end of myelination of the cortex and concomitant development of normal social and exploratory behavior (8 to 12 weeks) and the development of sexual maturity is considered to be the “juvenile” period (Scott and Fuller, 1965). Dogs are sexually mature by 6 to 9 months of age. If the dog is to be a breeding dog and does not show signs of sexual maturity by 6 to 9 months of age, further consultation is warranted. Sex hormones may interact with various neurodevelopmental systems, but no data exist on the effects of early versus later neutering on these systems in dogs, with the possible exception of correlates on long bone growth. Regardless, both neutered and intact animals are affected by behavioral concerns and pathologies.

We lack information on dogs that is now available for humans (and rodents), but it may be safe to assume that myelination and neuronal pruning occur rapidly for the first few months of life and then slow until social maturity, as is the pattern in humans. Social maturity is a period of renewed but progressive myelination and regressive pruning that is associated with changes in neurochemical profiles and shifts in behavior (Sowell et al., 1999). Behavioral changes attendant with canine social maturity begin at approximately 12 to 18 months. There is likely considerable variation attached to this estimate because of breed and size differences and because some dogs are still bred and selected for certain tasks. Such concerns are reduced for humans.

Social maturity is usually thought to end at about 24 to 36 months of age. The period of social maturity has never been well measured behaviorally, physiologically, or neurochemically through functional imaging in dogs, and so these are approximate ages around which much variation should occur, but if changes occur as they do for humans, these are reasonable landmarks. Given shared selection pressures on the development of behavior, we should expect dogs and humans to experience similar age-related developmental brain changes.

Humans are sexually mature at some point between 8 and 13 years of age, but are not socially mature—based on functional imaging and neurochemical evidence—until well into their 20s or 30s. As humans age from 6 to 17 years, cerebral gray matter volume decreases, and white matter and corpus callosum volumes increase, suggesting increased ability to integrate and act on information, when measured by magnetic resonance imaging (MRI) (De Bellis et al., 2001). Standard MRI assays reveal profound differences in size-by-age trajectories of brain development between males and females as they mature through age 27 years (De Bellis et al., 2001; Lenroot et al., 2007). Using diffusion tensor MRI, age-related (5 to 30 years) changes are seen in many areas of the human brain (i.e., deep gray matter, subcortical white matter, major white matter tracts) in a pattern that suggests that connections between the frontal and temporal lobes develop more slowly than other regions.

Patterns of change in maturation of the human frontal cortex appear to improve cognitive processing, a hypothesis supported by congruent data from electrophysiological, positron emission tomography, and neuropsychological studies on normal cognitive and neurological development (Sowell et al., 1999). Trajectories for regional brain maturation can be affected by trauma, indicating how important connecting tracts are in the development of adaptive behaviors. Children with post-traumatic stress disorder (PTSD) have larger prefrontal lobe cerebrospinal fluid volumes and smaller regional measurements of the corpus callosum than age-matched unaffected children; this finding is amplified for boys with PTSD (De Bellis and Kreshavan, 2003). We should hypothesize that the same pattern can occur with dogs.

These neurobehavioral developmental patterns that occur with social maturity have important implications for learning and acting on what is learned. The frontal cortex is especially involved in response inhibition, regulation of “emotion” and emotional outburst, organization of activities, and forethought involved in planning and problem solving in all species. It is unfortunate, especially given our evolved relationship with them, that we lack comparable data for dogs as they move from puppyhood through social maturity, but as imaging technologies become more accessible such data may emerge.

Why It Is Not about “Dominance”

The human social system is a fluid hierarchical one that is based on ability and/or age but that is grounded in the context of deference. Dogs also have fluid social structures where day-to-day interactions are largely based on deferential behaviors, especially where dogs are known to one another, and on behaviors designed to elicit information about risk in situations where they are not known to each other. Combat is the exceptional choice for resolution of conflict in both canids and humans. When combat is the first choice for conflict resolution, it is an abnormal, out-of-context behavior. Instead, agonistic behavior is generally accompanied by an elaborate display structure designed to minimize damage to the individual. Both canid and human social systems use signals and displays that minimize the probability of outright battle and the damage that could be incurred during fights.

Deferential relationships in neither dogs nor humans are structured as linear hierarchies. Most concepts involving “dominance” in dogs are outdated, something that the behavioral community has finally recognized (American Veterinary Society of Animal Behavior [AVSAB] Dominance Position Statement: and the Dog Welfare Campaign position statement: Many situations in which “dominance” is implicated in hierarchies may be artifacts. The study of relationships between fewer than six animals will automatically produce a numerical rank order hierarchy that is linear (Bernstein, 1981; Boyd and Silk, 1983; Rowell, 1974; Syme, 1974), but the ranks produced are unable to account for the social complexities that are noted. Instead, deferential behaviors are dependent on context and are based on knowledge, age, size, and the situation in which individuals are interacting. More information in language useful for clients can be found in the client handout, “Protocol for Generalized Discharge Instructions for Dogs with Behavioral Concerns.” It is not surprising that humans were able to incorporate dogs into our social groups, as we were incorporated into theirs.

How Dogs Communicate

Understanding Non-vocal Signals

Because dogs and people do have such similar social systems and use so many of the same signals, it has been very easy for people to assume that when a dog gives a signal that resembles a human signal, the message is exactly the same and that it means exactly the same thing (Smith, 1965). We have shared signals, but we should also understand that animals who do not use verbal speech in the manner we do and who do not have opposable thumbs may have their own signals that we could benefit from learning, rather than always expecting us to learn their signals. When humans allowed dogs to teach them to play using canine signals (bow and lunge), the relationship between the human and the dog improved, and dogs who had not played now played enthusiastically (Rooney and Bradshaw, 2001).

Behavioral descriptions are usually made on the basis of either structure (e.g., descriptions of postures or sounds) or consequences (e.g., the effect of the behavior on the individual exhibiting the behavior, others in the behavioral environment, and the behavioral environment itself). A good description of these concepts can be found at the Animal Behavior Society website ( The difficulty in veterinary behavioral medicine often arises when descriptions of measures and consequences are confused or given an associational or causal link without actually testing whether that link is valid or true. For descriptors to have scientifically valid causal or associational links, we would have to measure or assess whether these terms characterize what they were intended to characterize, an effort that is seldom made.

Early Behaviors

Early canine behaviors can be divided into et-epimeletic (care-seeking), epimeletic (caregiving), and allelomimetic (group-activity) behaviors. Until about 4 weeks of age, the relationship between the mother and puppies is primarily epimeletic. Box 4-2 contains the traditional classification of these stage-associated behaviors. Many of these behaviors are also seen later in life and can be understood by referring to this ontogenic history.

Systematic Approach to Understanding Canine Signals

Canine Visual Communication—What Can Dogs See?

Dogs are born with an immature and relatively non-myelinated visual system. Vision improves rapidly through 20 days of age.

With a 97-degree binocular field, dogs have relatively poor binocular vision compared with humans, but the extent to which they experience binocular vision depends on dog breed and head shape. Dogs have better lateral vision than humans, which may affect how they learn to understand the behaviors of other dogs. It should be noted that canine vision is exquisitely sensitive to movement—which is likely related to their excellent lateral vision—and dogs can recognize an object that is moving almost twice as well as when the same object is still. This finding has profound implications for dogs who are reactive to humans or other dogs.

Eye radius, a measure of size, positively correlates with the length and width dimensions of the skull but not with cephalic index, a measure of shape, rather than size (skull width/skull length × 100). Among breeds of domestic dogs, retinal ganglion cells range in distribution from a dense concentration in a strong area centralis, with virtually no visual streak, to a strong, horizontally distributed visual streak and almost no area centralis (McGreevy et al., 2004).

• Skull length was negatively correlated with peak area centralis density of ganglion cells but positively correlated with peak density of ganglion cells in the streak (e.g., long-nosed dogs have few ganglion cells in the area centralis but a lot of ganglion cells in the streak).

• The ratio of ganglion cell densities in the area centralis to cells in the streak was negatively correlated with skull length (i.e., the more cells in the area centralis compared with the streak, the shorter the skull).

• Dolichocephalic dogs have strong visual streaks and relatively low densities of ganglion cells in the area centralis, and brachycephalic dogs have concentrated ganglion cells in the area centralis and low to no concentrations in a visual streak.

• Red/green cones (medium to long wave) were denser in the temporal region than in the area centralis in brachycephalic dogs and less concentrated in the temporal retina in dolichocephalic dogs. Blue cones (short wave) were sparse compared with red/green cones in all dogs.

• The number of ganglion cells correlates positively with skull size. McGreevy et al. (2004) did not examine the extent to which skull shape and size may have affected distribution of olfactory neurons, but it may be prudent to expect an effect.

We seldom consider what selective breeding to produce dogs of different shapes, looks, and work attributes has done to the senses of dogs, but it now appears that there may be effects for some aspect of how dogs see. If this is true, some of the behaviors seen in long-nosed versus short-nosed dogs may be the result of how they perceive their world.

Dogs see in rudimentary color vision (dichromatic), and they are sensitive to short-wave (bluish) light. Dog color vision is sufficiently discriminating so that they can pick out an object based on color (Neitz et al., 1989). Dogs have two classes of photopigment in cones with spectral peaks at approximately 429 nm (blue) and 555 nm (green), the peak of sensitivity for light-adapted eyes. In bright light, however, dogs have less acute vision than humans. Rhodopsin in dogs has a peak sensitivity to wavelengths of 506 to 510 nm and requires more than an hour to regenerate completely after exposure to bright light. The extent to which rods and cones develop is dependent on early exposure to a full range of ambient light conditions and to critical nutrients docosahexaenoic acid (DHA).

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Aug 15, 2016 | Posted by in SMALL ANIMAL | Comments Off on Normal Canine Behavior and Ontogeny: Neurological and Social Development, Signaling, and Normal Canine Behaviors

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